Very short Answer type Questions [1 mark each]

Transcription

1 Very short Answer type Questions [1 mark each] 1. Why must electrostatic field at the surface of a charged conductor be normal to the surface at every point? Give reason. 2. What is meant by the statement that the electric field of a point charge has spherical symmetry whereas that of an electric dipole is cylindrically symmetric? 3. Two charges of magnitudes 2Q and + Q are located at points (a, 0) and (4a, 0) respectively. What is the electric flux due to this charge through a sphere of radius 3a with its center at the origin? 4. Why do the electric field lines never cross each other? 5. Define electric dipole moment. Is it scalar or vector? 6. An electric dipole is placed, in a uniform electric field. What is net force acting on it? 7. How does the force between two point charges change if the dielectric constant of the medium in which they are kept increase? 8. Under what conditions, the electric lines of force are straight? 9. Why do the electrostatic field lines not form closed loops? 10. Draw an equipotential surface in a uniform electric field. 11. The given graph shows the variation of charge 'Q' versus potential difference 'V' for capacitors C1 and C2. The two capacitors have the same plate separation, but the plate area of C2 is double that of C1, which of the lines in the graph correspond to C1 and C2 and why? Q A B V 12. When kept in an electric field, does a proton move from lower to higher potential or from higher to lower potential? 13. In a medium, the force of attraction between two point electric charges, distance d apart is F. What distance apart should these be kept in the same medium so that the force between them becomes (i) 3 F (ii) F/ 3?

2 14. A metallic sphere is charged negatively. Will its mass increase, decrease or remain the same? 15. Give three differences between the nature of electric potentials of a single point charge and an electric dipole. 16. The potential energy of an electric dipole placed in a uniform electric field is zero. What is the orientation of vector P and vector E? 17. In parallel plate capacitor, the capacitance increases from 4μF to 80 μf, on introducing a dielectric medium between the plates. What is the dielectric constant of the medium? 18. An electric dipole of dipole moment 20 X10 6 C m. It is enclosed by a closed surface. What is the net electric flux coming out of surface? 19. What is the amount of work done in moving a 100 μc charge between two points 5 cm apart on an equipotential surface? Very short Answer type Questions [2 marks each] 20. Although ordinary rubber is insulator, the rubber tyres of air craft are made slightly conducting. Why? 21. Figure shows three charges + 2q, -q and + 3q. Two charges +2q and q are enclosed within a surface S. What is the electric flux due to this configuration through the surface S? 22. A system has two charges qa = C and qb = C located at points A: (0, 0, 15 cm) and B: (0,0, +15 cm), respectively. What are the total charge and electric dipole moment of the system? 23. How much work is required in turning an electric dipole of dipole moment p - > from its position of stable equilibrium to its position of unstable equilibrium in a uniform electrostatic field? 24. Two fixed point charges +4e and +e units are separated by a distance 'a'. Where should the third point charge be placed for it to be in equilibrium? 25. A point charge of 1.8 μc is at the center of a cubical Gaussian surface having each side 50 cm. What is the net electric flux through the surface? 26. Electric field intensity in a given region is zero. Can we conclude that electric potential must be zero?

3 27. What is the work done in moving a 2μC point charge from corner A to corner B of square ABCD. When a 10 μc charge exists at the center of the square? Short Answer Type Questions-II [3 marks each] 28. Define electric flux. Write its S.I. units. A spherical rubber balloon carries a charge that is uniformly distributed over its surface. As the balloon is blown up and increases in size, how does the total electric flux coming out of the surface change? Give reason. 29. Derive the expression for the energy stored in a parallel plate capacitor with air between the plates. How does the stored energy change if air is replaced by a medium of dielectric constant K? 30. A parallel plate capacitor with air as dielectric is connected to a power supply and charged to a potential difference Vo. After disconnecting from power supply, a sheet of insulating material is inserted between the plates completely filling the space between them. What will be the effect on (i) charge on the plates (ii) electric field between the plates (iii) potential difference between the plates (iv) capacitance (v) energy stored in the capacitor. 31. An electric dipole consists of two opposite charges of magnitude 1μC each and is separated by a distance of 3 cm. The dipole is placed in an electric field of N/C. Find the maximum torque on the dipole. 32. A slab of material of dielectric constant K has the same area as that of the plates of a parallel plate capacitor but has the thickness d/2, where d is the separation between the plates. Find out the expression for its capacitance when the slab is inserted between the plates of the capacitor. 33. A parallel plate capacitor, each of plate area A and separation d between the two plates, is charge with charges + Q and Q on the two plates. Deduce the expression for the energy stored in the capacitor. 34. State Gauss s theorem. Apply this theorem to obtain an expression for the electric field intensity at a point due to an infinitely long uniformly charged straight wire. 35. Define electric field intensity. Write its S.I. unit. Write the magnitude and direction of electric field intensity due to an electric dipole of length 2a at the mid-point of the line joining the two charges

4 36. An electric dipole with moment P is placed in a uniform electric field E. Write the expression for the torque experienced by the dipole. Identify two parts of perpendicular vectors in the expression. Show diagrammatically the orientation of the dipole in the field for which the torque is (i) maximum (ii) half the maximum value (iii) zero. 37. Derive an expression for electric potential due to an electric dipole at any point on its axis. Mention the contrasting feature of electric potential of a dipole at a point as compared to that due to a single charge. 38. A slab of material of dielectric constant K has the same area as that of the plates of a parallel plate capacitor but has the thickness 2d/3, where d is the separation between the plates. Find out the expression for its capacitance when the slab is inserted between the plates of the capacitor. 39. An oil drop of 12 excess electrons is held stationary under a constant electric field of 2.55x10 4 N/C. Estimate the radius of the drop. (density of oil = 1.26 g cm -3,g=9.81 ms -2 and e= 1.6x10-19 C). Long Answer Type Questions [5 marks each] 40 (a)deduce an expression for the capacitance of a parallel plate capacitor with air as the medium between the plates (b)a dielectric slab of thickness t is kept in between the plates each of area A of parallel plate capacitor separated by a distance of d. Drive an expression for the capacitance of capacitor for t <<d. 40 (b) Using Gauss law, derive an expression for the electric field intensity at any point outside a uniformly charged thin spherical shell of radius R and charge density σ C/m - 2 Draw the field lines when the charge density of the sphere is (i) positive, (ii) negative. (b) A uniformly charged conducting sphere of 2m in diameter has a surface charge density of 100μC/m -2. Calculate the (i) charge on the sphere (ii) total electric flux passing through the sphere. 41. Define the term electric dipole moment. Give its unit. Derive an expression for the maximum torque acting on the electric dipole when held in uniform electric field. In which orientation, a dipole placed in a uniform electric field is in (i) stable, (ii) unstable equilibrium?

5 42. Derive an expression for the torque experienced by an electric dipole kept in a uniformly electric field. 43. Two charged particles, having equal charges of C each, are brought from infinity to within a separation of 10 cm. Find the increase in the electric potential energy during the process. 44. The electric field components due to a charge inside the cube of side 0.1m Are as shown: E x = x where NmC -1 Calculate (i) the flux through the cube and (ii) the charge inside the cube. 45. Use Gauss s law to obtain an expression for the electric field due to an infinitely long straight uniformly charged wire Electric field in the above figure is directed along + X direction and given by Ex = 5Ax + 2B, where E is in NC -1 and x is in metre, A and B are constants with dimensions. Talking A=10N/C/m and B = 5N/C calculate. (i) the electric flux through the cube. (ii) net charge enclosed within the cube.

6 47. An electric dipole with moment P is placed in a uniform electric field E. Write the expression for the torque experienced by the dipole. Identify two parts of perpendicular vectors in the expression. Show diagrammatically the orientation of the dipole in the field for which the torque is (i) maximum (ii) half the maximum value (iii) zero. 48. (i) explain briefly how a capacitor stores energy on charging. Obtain expression for energy stored. (ii) A parallel plate capacitor of plate separation s is charged to a p.d. V. A dielectric slab of thickness d and dielectric constant K is introduced between the plates while the battery remains connected to the plates. (a) Find the ratio of energy stored in the capacitor after and before the dielectric in introduced, give physical explanation for this charge in stored energy. (b) What happens to the charge on the capacitor? (c) How does the electric field between plates change. ********************************************************************************************************

7 Very short Answer type Questions [1 mark each] 1. Name the quantity that can be found from the slope of the graph of Current density j and drift velocity Vd of the charge carriers. 2. Two identical cells, each of emf E, having negligible internal resistance, are connected in parallel with each other across an external resistance R. What is the current through this resistance? 3. Two materials, Ag and GaAs, are cooled from 300 K to 60 K. What will be the effect on the resistivity? 4. Why are the connecting resistors in a meter bridge made of thick copper strips? 5. Define the term drift velocity of charge carriers in a conductor and write its relationship with the current flowing through it. 6. Sketch a graph showing variation of resistivity of carbon with temperature. 7. Explain how the average velocity of free electrons in a metal at constant temperature, in an electric field, remains constant even though the electrons are being constantly accelerated by this electric field? 8. Why potentiometer is preferred over voltmeter for measuring emf. 9. What is meant by the sensitivity of a potentiometer? Very short Answer type Questions [2 marks each] 10. The V-I graphs of two resistors, and their series combination, are

8 shown in the adjoining figure. Which one of these graphs represents the series combination of the other two? Give reasons for your answer. 11. Name the two factors on which the resistivity of a given material depends. A carbon resistor has a value of 62K with a tolerance of 5%. Give the colour code for this resistor. 12. V-I graph for a metallic wire at two different temperatures T1 and T2 is as shown in the following figure. Which of the two temperatures is higher and why? 13. The V-I graphs of two resistors of the same material and the same radii with lengths L1 and L2 are shown in fig. If L1 > L2, state with reason which of these graphs represents voltage current change for L A cell of emf 2 V and internal resistance 0.1 Ω is connected to a 3.9 Ω external resistance. What will be the p.d. across the terminals of the cell? 15. A potential difference V is applied to a conductor of length L. How is the drift velocity affected when V is doubled and L is halved?

9 16. A cell of 6 V and internal resistance 2Ω is connected to a variable resistor. For what value of current does maximum power dissipation occur in the circuit? 17. The plot of the variation of potential difference across a combination of three identical cells in series, versus current is as shown below. What is the emf of each cell? 18. The resistance of the platinum wire of a platinum resistance thermometer at the ice point is 5Ω and at steam point is 5.23Ω. When the thermometer is inserted in a hot bath, the resistance of the platinum wire is 5.795Ω. Calculate the temperature of the bath. 19. A cell of emf (E) and internal resistance (r) is connected across a variable external resistance (R). Plot graphs to show variation of (i) E with R, (ii) Terminal p.d. of the cell (V) with R. 20. Find the value of the unknown resistance X in the circuit if no current flows through the galvanometer. Assume the resistance per unit length of the wire is 0.01Ωcm Given n resistors each of resistance R, how will you combine them to get the (i) maximum (ii) minimum effective resistance? What is the ratio of the maximum to minimum resistance? 22. Draw V-I graph for ohmic and non- ohmic materials. Give one example for each. 23. In a potentiometer arrangement, a cell of emf 1.25 V gives a balance point at 35.0cm length of the wire. If the cell is replaced by another cell and the balance point shifts to 63.0cm, what is the emf of the second cell? Is the balance point affected by the internal resistance of the driver cell? Short Answer Type Questions-II [3 marks each] 24. In the potentiometer circuit shown, the balance point is at X. State with reason where the balance point will be shifted when (i)resistance R is increased, keeping all parameters unchanged. (ii)resistance S is increased keeping R constant.

10 (iii)cell P is replaced by another cell whose emf is lower than that of that cell Q. 25.A potentiometer wire of length 1.0 m has a resistance of 15 Ω. It is connected to a 5 V battery in series with a resistance of 5 Ω. Determine the emf of the primary cell which gives a balance point at 60 cm. 26. When two identical cells E and internal resistance r each are connected in series with a resistor R = 10, a current of 0.75 A flows in the circuit. Just one cell across the same R, however, sends a current of 0.50 A. Find the emf and internal resistance of the cell. 27. Describe briefly, with the help of a circuit diagram, how a potentiometer is used to determine the internal resistance of a cell. 28. Explain the term drift velocity of electrons in a conductor. Hence obtain the expression for the current through a conductor in terms of drift velocity. 29. Answer the following: (a) Why are the connections between the resistors in a meter bridge made of thick copper strips? (b) Why is it generally preferred to obtain the balance point in the middle of the meter bridge wire? (c) Which material is used for the meter bridge wire and why? 30.E2 =1.02V, PQ=1m.When switch S open, null position is obtained at a distance of 51 cm from P. Calculate (i) potential gradient (ii) emf of the cell E1 (iii) when switch S is closed, will null point move towards P or Q. Give reason for your answer

11 31. Using data given in graph determine (i) emf (ii) internal resistance of the cell. (iii) For what current, does maximum power dissipation occur in the circuit? 32. In a meter bridge the null point is found at a distance of 33.7cm from A, when resistance R is connected in left gap and S is connected in the right gap. If now a resistance of 12Ω is connected in parallel with S, the null point occurs at 51.9cm. Determine the values of R and S. 33. Two students X and Y perform an experiment on potentiometer separately using the circuit keeping other things unchanged (i) X increases the value of distance R. (ii) Y decreases the value of resistance S in the set up. How would these changes affect the position of null point in each case and why? 34.How does the drift speed of the electrons change through a metal wire if (a) potential difference is increased. (b) temperature is increased. (c) metal wire is stretched. 35.Two wires of equal length, one of aluminum and the other of copper have the same resistance. Which of the two wires is lighter? Hence explain why aluminum wires are preferred for overhead power cables.(ρ Al =2.63X10-8 Ωm, ρ Cu =1.72 X 10-8 Ωm, Relative density of Al= 2.7, of Cu = 8.9) 36.A potentiometer wire of length 100cm has a resistance of 10Ω is connected in series with a resistance and cell of emf 2V of negligible internal resistance. A source of emf of 10mV is balanced against a length of 40cm of potentiometer

12 wire. What is the value of the external resistance? 37. In a potentiometer circuit of a battery of negligible internal resistance is set up as shown to develop a constant potential gradient along the wire AB. Two cells of emf E1 and E2 are connected in series as shown in the combination (1) and (2). The balance points are obtained respectively at 400cm and 240cm from the point A. Find (i) E1/ E2 and (ii) balancing length for the cell E1 only. E 1 E 2 G E 1 E 2 Long Answer Type Questions [5 marks each] 38. State the principle of potentiometer. Draw a circuit diagram to show the use of potentiometer to compare the emf of two primary cells. Write the formula used. How can the sensitivity of a potentiometer be increased. 39. Are the paths of electrons straight lines, between successive collisions, in the (i) absence of electric field (ii) presence of electric field. Establish a relation between drift velocity and current. Hence obtain the relation between current density and drift velocity. 40. Deduce the condition for balance in a Wheatstone bridge. Using the principle of Wheatstone bridge, describe the method to determine the specific resistance of a wire in the laboratory. Draw the circuit diagram and write the formula used. Write any two precautions. ********************************************************************************************************

13 Very short Answer type Questions [1 mark each] 1. What is the direction of the force acting on a charge particle q, moving with a velocity v in a uniform magnetic field B? 2. Define one tesla using the expression for the magnetic force acting on a particle of charge q moving with velocity v in a magnetic field B 3. How will the magnetic field at the center of a circular coil carrying current change if the current through the coil is double and the radius of the coil is halved? 4. Magnetic field lines can be entirely confined within the core of a toroid, but not within a straight solenoid. Why? 5. An electron does not suffer any deflection while passing through a region of uniform magnetic field. What is the direction of the magnetic field? 6. A beam of a particles projected along +x-axis, experiences a force due to a magnetic field along the +y-axis. What is the direction of the magnetic field? 7. Mention the two characteristic properties of the material suitable for making core of a transformer. 8. An electron is moving along positive x- axis in the presence of uniform magnetic field along positive y -axis. What is the direction of the force acting on it? 9. Where on the surface of the earth is the vertical component of earth s magnetic field zero? 10. Steel is preferred for making permanent magnets whereas soft iron is preferred for making electromagnets.give one reason. 11. A narrow beam of protons and deuterons, each having the same momentum, enters a region of uniform magnetic field directed perpendicular to their direction of momentum. What would be the ratio of the circular paths described by them? 12. Why should the spring or suspension wire in a moving coil galvanometer have low torsional constant? 13. Where on the surface of Earth is the angle of dip zero? 14. The permeability of a magnetic material is Name the type of magnetic materials it represents.

14 Very short Answer type Questions [2 marks each] 15. An electron and a proton moving with the same speed enter the same magnetic field region at right angles to the direction of the field. Show the trajectory followed by the two particles in the magnetic field. Find the ratio of the radii of the circular paths which the particles may describe. 16. The vertical component of Earth s magnetic field at a place is 3 times the horizontal component. What is the value of angle of dip at this place? 17. Two current carrying loops carrying current I each and radii r each are place coaxially such that their centers are separated by a distance r. If the current flowing in the coils are in same sense as observed by an observer from one side then find the magnitude of magnetic field at the mid point of the line joining their centers. 18. Define the term magnetic dipole moment of a current loop. Write the expression for the magnetic moment when an electron revolves at a speed v, around an orbit of radius r in hydrogen atom. 19. Define magnetic susceptibility of a material. Name two elements, one having positive susceptibility and the other having negative susceptibility. What does negative susceptibility signify? 20. Draw magnetic field lines when a (i) diamagnetic, (ii) paramagnetic substance is placed in an external magnetic field. Which magnetic property distinguishes this behaviour of the field lines due to the two substances? 21. How can a galvanometer be converted into a voltmeter to read a maximum potential difference V? Discuss with related mathematical expression. 22. How will you convert a galvanometer into an ammeter of range 0 - I amperes? What is the effective resistance of an ammeter? 23. When a magnetic needle placed inside a uniform magnetic field a torque developed on it, give the condition of most stable and most unstable position of magnetic needle in the magnetic field. 24. State the factors on which the force acting on a charge moving in a magnetic field depends. Write the expression for this force. When is this force minimum and maximum? Short Answer Type Questions-II [3 marks each] 25. A long straight wire of a circular cross-section of radius a carries a steady current I. The current is uniformly distributed across the cross-section. Apply Ampere s circuital law to calculate the magnetic field at a point r in the region for (i) r < a and (ii) r > a. 26. Define current sensitivity and voltage sensitivity of a galvanometer. Increasing the current sensitivity may not necessarily increase the voltage sensitivity of a galvanometer. Justify.

15 27. Explain how an atom behaves as a magnetic dipole. Derive an expression for the magnetic dipole moment of the atom. Also define Bohr magneton. 28. A steady current (I1) flows through a long straight wire. Another wire carrying steady current (I2) in the same direction is kept close and parallel to the first wire. Show with the help of a diagram how the magnetic field due to the current I1 exerts a magnetic force on the second wire. Write the expression for this force. 29. Define the terms (i) magnetizing field, (ii) magnetic intensity, (iii)relative permeability and (iv) magnetic susceptibility. Give their S I unit, if any 30. A long solenoid with closely wound turns has n turns per unit of its length. A steady current I flows through this solenoid. Use Ampere s circuital law to obtain an expression for the magnetic field at a point on its axis and close to its mid point. 31. Define current sensitivity and voltage sensitivity of a galvanometer. State the factors on which the sensitivity of a moving coil galvanometer depends. Long Answer Type Questions [5 marks each] 32. Derive a mathematical expression for the force per unit length acting on each of the two straight parallel metallic conductors carrying current in the same direction and kept near each other. Hence define an ampere. Why do such current carrying conductors attract each other? 33. With the help of a neat and labeled diagram, explain the underlying principle, construction and working of a moving coil galvanometer. What is the function of (i) uniform radial field (ii) soft iron core in such a device? 34. Derive an expression for the torque on a rectangular coil of area A, carrying a current I and placed in a magnetic field B. The angle between the direction of B and vector perpendicular to the plane of the coil is. 35. State the principle of a cyclotron. Draw labeled diagram. Explain briefly how it works and how it is used to accelerate the charged particles. Show that the time period of ions in a cyclotron is independent of both the speed and radius of circular path. 36. What is resonance condition? How is it used to accelerate the charged particles? (i) Explain the use of electric field &magnetic field. (ii) Electron cannot be accelerated, why? 37. Discuss the motion of a charged particle in a uniform magnetic field with initial velocity (i) parallel to the field, (ii) perpendicular to the magnetic field and (iii) at an arbitrary angle with the field direction. 38. Using Biot-Savart law, deduce an expression for the magnetic field on the axis of a circular current loop. Hence obtain the expression for the magnetic field at the center of the loop.

16 Very short Answer type Questions [1 mark each] 1. Define the term watt-less current. 2. What is the function of a step down transformer? 3. The peak value of emf in a.c. in E0. Write its (i) rms and (ii) average value over a complete cycle. 4. What is the power dissipated in an a.c. circuit in which voltage and current are given by V=230 sin (ωt+π/3) and I = 10 sin ωt? 5. A bulb and a capacitor are connected in series to an a.c. source of variable frequency. How will the brightness of the bulb change on increasing the frequency of the a.c. Source? Give reasons. 6. Two identical loops, one of copper and another of constantan are removed from a magnetic field within the same time interval. In which loop will the induced current be greater? 7. The power factor of an a.c. circuit is 0.5. What will be the phase difference between voltage and current in this circuit? 8. In a series LCR circuit, the voltage across an inductor, capacitor and resistor are 20V, 20V and 40V respectively. What is the phase difference between the applied voltage and the current in the circuit? 9. When current in a coil changes with time, how is the back emf induced in the coil related to it? 10. The instantaneous current and voltage of an a.c. circuit are given by i = 10 sin (314 t) A and V = 50 sin (314t + π/2) V. What is the power of dissipation in the circuit?

17 11. Define self-inductance. Give its S.I. units. 12. A rectangular loop of wire is pulled to the right, away from the long straight wire through which a steady current I flows upwards. What is the direction of induced current in the loop? Very short Answer type Questions [2 marks each] 13. Two loops of different shapes are moved in a region of uniform magnetic field in the directions marked by arrows as shown in the figure. What is the direction of the induced current in each loop? 14. Two bar magnets are quickly moved towards a metallic loop connected across a capacitor C as shown in figure. Predict the polarity of the capacitor. 15. The current flowing through a pure inductor of inductance 4mH is I = 12 cos (300t) ampere. What is the (i) rms (ii) average value of current for a complete cycle? 16. A closed loop PQRS of wire is moved into a uniform magnetic field at right angles to the plane of the paper as shown in the figure. Predict the direction of induced current in the loop. 17. A bar magnet is moved in the direction indicated by the arrow between two coils PQ and CD. Predict the directions of induced current in each coil.

18 18. Predict the direction of induced current in metal rings 1 and 2 when current I in the wire is steadily decreasing? 19. Predict the direction of induced current in a metal ring when the ring is moved towards a straight conductor with constant speed v. the conductor is carrying current I in the direction shown in the figure. 20. How does the mutual inductance between two coils change when (i) distance between the coils is increased and (ii) number of turns in the coils is increased? 21. Draw the graphs showing the variations of (i) inductive reactance, and (ii) capacitive reactance, with frequency of applied voltages in a.c. circuit. 22. A perfect self-inductor when connected to an a.c. source does not produce heating effect yet reduces the current in the circuit. Explain. 23. Prove that an ideal capacitor, in an a.c. circuit does not dissipate power. 24. Derive an expression for the self-inductance of a long air-cored solenoid of length l and number of turns N. 25. (i) How are eddy currents reduced in a metallic core? (ii) Give two uses of eddy currents. 26. Current in a circuit falls from 5 A to 0 A in 0.1s. If an average emf of 200V induced, give an estimate of the self-inductance of the circuit. 27. Two identical loops, one of copper and the other of aluminium, are rotated with the same angular speed in the same magnetic field. Compare (i) the induced emf and (ii) the current produced in the two coils. Justify your answer.

19 28. A coil Q is connected to low voltage bulb B and placed near another coil P is shown in the figure. Give reason to explain the following observations: (a) The bulb B lights. (b) Bulb gets dimmer if the coil Q is moved towards left. Short Answer Type Questions-II [3 marks each] 29. Mention the factors on which the resonant frequency of a series LCR circuit depends. Plot a graph showing variation of impedance of a series LCR circuit with the frequency of the applied a.c. source. 30. (a) Distinguish between the terms resistance, reactance and impedance of an a.c. circuit. (b) A 100µF capacitor in series with a 40Ω resistance is connected to a 100V, 60 Hz supply. Calculate (i) the reactance (ii) the impedance and (iii) maximum current in the circuit. 31. A circular coil of radius 8cm and 20cm turns rotates about its vertical diameter with an angular speed of 50 s -1 in a uniform horizontal magnetic field of magnitude 3 x 10-2 T. Find the maximum and average value of emf induced in the coil. 32. State the underling principle of an a.c. generator. Write the relationship between the peak value and rms value of alternating voltage. 33. In the following circuit, calculate (i) the capacitance of the capacitor if the power factor of the circuit is unity and (ii) the Q- factor of the circuit. 34. An inductor 200 mh, a capacitor C and a resistor 10 ohm are connected in series with a 100 V, 50 s -1 a.c. source. If the current and voltage are in phase with each other, calculate the capacitance of the capacitor.

20 35. A capacitor and a resistor are connected in series with an a.c. source. If the potential difference across C,R are 120V, 90 V respectively and if the rms current of the circuit is 3 A, calculate the (i) impedance, (ii) power factor of the circuit. 36. An alternating voltage of frequency f is applied across a series LCR circuit. Let fr be the resonant frequency for the circuit. Will the current lag, lead of remain in phase with the applied voltage when (i) f>fr (ii) f<fr? Explain your answer in each case. 37. A conducting rod of length l is moved in a magnetic field of magnitude B with velocity v such that the arrangement is mutually perpendicular. Prove that the emf induced in the rod is = ɛ Blv. 38. Derive an expression for the impedance of an a.c. circuit consisting of an inductor, capacitor and a resistor. 39. Obtain the expression for the mutual inductance of a pair of coaxial circular coils of radii r and R(R >r) placed with their centers coinciding. 40. A jet plane is travelling west at 450 ms - 1. If the horizontal component of earth s magnetic field at that place is 4 x10-4 tesla and the angle of dip is 30, find the emf induced between the ends of wings having a span of 30 m. 41. A town situated 20 km away from a power plant generating power at 440 V, requires 600kw of electric power at 220V. The resistance of the two wire lines carrying power is 0.4Ω per km. The town gets power from the line through a V step down transformer at a substation in the town. (i) Find the line power losses in the form of heat. (ii) How much power must the plant supply, assuming there is negligible power loss due to leakage? (iii) Characteristics the step up transformer at the plant. 42. Define self-inductance of a coil. Show that magnetic energy required to build up the current I in a coil of self-inductance L is given by ½LI State Lenz s law. A metal rod held horizontally along east-west direction, is allowed to fall under gravity. Will there be an emf induced at its ends? Justify your answer. 44. A Resistor of 200Ω and a capacitor of 15.0μF are connected in series to a 200 V, 50 Hz ac source.(i) Calculate the current in the circuit; (b) Calculate the rms voltage across the resistor and the capacitor. Is the algebraic sum of these voltages more than the source voltage? If yes, resolve the paradox. Long Answer Type o A

21 [5 marks each] o Long Answer Type Questions [5 marks each] 45. (a) What is induced emf? Write Faraday s law of electromagnetic induction. Express it mathematically. (b) A Conducting rod of length l with one end fixed, is rotated with a uniform angular speed ɷ in a vertical plane, normal to a uniform magnetic field B. deduce an expression for the emf induced in this rod. (c) In India domestic power supply is at 220V, 50Hz, while in USA it is 110V, 50Hz. Give one advantage and one disadvantage of 220V supply over 110V supply. 46. Three students X, Y, and Z performed an experiment for studying the variation of alternating currents with angular frequency in a series LCR circuit and obtained the graphs shown below. They all used a.c. sources of the same r.m.s. value and inductances of the same value. What can we (qualitatively) conclude about the (i) capacitance value (ii) resistance values used by them? In which case will the quality factor be maximum? What can we conclude about nature of the impedance of the set up at frequency ὠo? 47. (a) The given graphs represent the variation of the opposition offered by the circuit to flow of alternating current with frequency of the applied emf. Identify the circuit element corresponding to each graph. (b) A Circuit is set up by connecting L=100 mh, C= 5µF and R=100Ω in series. An alternating emf of Volt. 500/ Hz is applied across this series combination. Calculate the impedance of circuit. What is the average power dissipated in (i) the resistor (ii) the capacitor (iii) the inductor and (iv) the complete circuit. ****************************************************************************************************

22 Very short Answer type Questions [1 marks each] 1. Identify the E.M. wave that is used in burglar alarms. Give its wavelength and frequency. 2. When can a charge act as a source of electromagnetic waves? 3. Which part of electromagnetic spectrum has highest frequency? 4. What is the source of X-ray? 5. Identify the em waves used in remote control. 6. Which radiation is released in nuclear reactions? OR Name the radiation involve in nuclear reaction. 7. Write the use of infrared waves. 8. Name the part of electromagnetic spectrum of wavelength 10-2m and mention its applications? 9. Which part of electromagnetic spectrum has largest penetrating power? What is its frequency range? 10. Write the following radiations in an ascending order in respect of their frequencies: X-rays, microwaves, ultraviolet rays and radio waves. 11. What is the ratio of speed of gamma rays and radio waves in air? 12. Name the electromagnetic radiations used for viewing objects through haze and fog. 13. Name the electromagnetic radiations used for studying crystal structure of solids. 14. What is the ratio of speed of gamma rays and radio waves in vacuum? 15. Which part of electromagnetic spectrum does the wavelength m corresponds to? 16. What is the phase difference between electric and magnetic field vectors? 17. Give a reason to show that micro waves are batter carrier of signal for long range transmission than radio waves.

23 Very short Answer type Questions [2 marks each] 18. A plane electromagnetic wave travels in vacuum along z-direction. What can you say about the directions of its electric and magnetic field vectors? If the frequency of the wave is 30 MHz, what is its wavelength? 19. Name the characteristics of electromagnetic waves that (i) increases (ii) remains constant in the electromagnetic spectrum as one moves from radio wave region towards ultraviolet region. 20. What modification was made by Maxwell in Ampere circuital law? 21. find the wave length of electromagnetic waves of frequency 5x10 19 Hz in free space. Give its two applications. 22. Write the electromagnetic wave whose wavelength is 1nm to 10-3 nm & write its one application? 23. A radio can tune in to any station in the 7.5 MHz to 12 MHz band. What is the corresponding wavelength band? Name the part of the electromagnetic spectrum of frequency 10 Hz and mention its application. 25. Identify the radiation and give their one application (I)Is used for studying crystal structure. (ii)produces intense heating effect. 26. Write the following radiations in an ascending order with respect of their frequencies Gamma rays, Infra red, Visible light, Radio waves. 27. Mentioned four important facts about em waves. Short Answer type Questions [3mark each] 28. Which constituent radiation of electromagnetic spectrum is used in (1) radar (2) to photograph internal parts human body (3) for taking photograph of the sky during light and foggy condition? Give one reason for your answer in each case. 29. When can a charge act as source of electromagnetic wave? How are the directions of electric and magnetic fields vectors, in an electromagnetic wave, related to each other and to the direction of propagation of the wave?

24 Which physical quantity has the same value for the waves belonging to the different parts of the electromagnetic spectrum? 30. The velocity of propagation (in vacuum) and the frequency of (i) X-rays and (ii) Radio waves are denoted by (vx, nx) and (vr, nr) respectively. How do the values of (i) v x and v r (ii) n x and n r Compare with each other? 31. Why are infrared radiations referred to as heat waves also? Name the radiations which are next to these radiations in electromagnetic spectrum having (i) Shorter wavelength. (ii) Longer wavelength. 32. The oscillating magnetic field in a plane EM wave is given by sin 2 10 t 300 x Tesla (i) (ii) (i) B y = Calculate the amplitude of Electric field. Write down the expression for the oscillating electric field. 33. Given below are some famous numbers associated with electromagnetic radiations indifferent contexts in physics. State the part of the electromagnetic spectrum to which each belongs. (a) 21 cm (wavelength emitted by atomic hydrogen in interstellar space). (b) 1057 MHz (frequency of radiation arising from two close energy levels in hydrogen; known as Lamb shift). (c) 2.7 K [temperature associated with the isotropic radiation filling all space-thought to be a relic of the big-bang origin of the universe]. (d) 5890 Å Å [double lines of sodium] (e) 14.4 kev [energy of a particular transition in 57Fe nucleus associated with a famous high resolution spectroscopic method (Mössbauer spectroscopy)]. 35. Identify the following part of em waves which (a) has its wavelength range between 390 nm & 770 nm (b) Is absorbed by ozone layer.. (c) Produces intense heating effect.

25 OPTICS Very short Answer type Questions [1 mark each] 1. An object is held at the principal focus of a concave lens of focal length f. Where is the image formed? 2. Light waves can be polarized while sound waves cannot be, why? 3. Why do welders wear special dark glass goggles or face masks with glass window? Justify your answer. 4. Write the two differences between interference and diffraction. 5. In which direction relative to the normal, does a ray bend, when it enters obliquely a medium in which its speed is increased? 6. What is the focal length of a plane mirror? 7. What happen to the value of the focal length of a convex lens and concave mirror they immersed in water? 8. What is the geometrical shape of the wavefront when a plane wave passes through a convex lens? 9. A diverging lens of focal length F is cut into two identical parts each forming a plano-concave lens. What is the focal length of each part? 10. How the angular separation of interference fringes in Young s double slit experiment change when the distance between the slits and screen is doubled? Short Answer Type Questions-I [2 marks each] 11. A glass lens of refractive index 1.45 disappears when immersed in a liquid. What is the value of refractive index of the liquid? 12. A converging lens is kept co-axially in contact with a diverging lens both the lenses being of equal focal lengths. What is the focal length of the combination? 13. For the same value of angle incidence, the angles of refraction in three media A, B and C are 15, 25 and 35 respectively. In which medium would the velocity of light be minimum?

26 14. In a single-slit diffraction experiment, the width of the slit is made double the original width. How does this affect the size and intensity of the central diffraction band? 15. How does the fringe width, in Young s double-slit experiment, change when the distance of separation between the slits and screen is doubled? 16. (i) What is the relation between critical angle and refractive index of a material? (ii) Does critical angle depend on the colour of light? Explain. 17. A convex lens has power 10D. It is immersed in a liquid, then it behaves as concave lens having focal length 50 cm. Find refractive index of the liquid ga 1.5 (given ) 18. Explain refraction of wave front using Huygens's Principle. 19. In Young s double slit experiment if the distance between two slits is halved and distance between the slits and the screen is doubled, then what will be the effect on fringe width 20. How the intensity of maxima and minima in the Young will s double slit experiment change, if one of the two slits is covered by a transparent paper which transmits only half of the light intensity? 21. Draw a labeled ray diagram showing the formation of image by a compound microscope. State the expression for its magnifying power. 22. How does the fringe width of interference fringes change, when the whole apparatus of Young s double slit experiment is immersed in a liquid if refractive index 1.3? 23. State reasons to explain these observationsa. The bluish colour predominates in clear sky. b. Violet color is seen at the bottom of the spectrum when white light is dispersed by a prism. 24. A convex lens made of glass of refractive index µl, is immersed in medium of refractive index µm. How will the lens behave when µl>µm. 25. A ray is to be deviated through 90 by a right- angled isosceles prism. What should be the minimum refractive index of the material of the prism? 26. Two thin lenses of power +7D and -3D are in contact.what is the focal length of the combination? 27. Explain how the focal length of a convex lens changes with increase in wavelength of incident light.

27 28. On what factors does (i) magnifying power and (ii) resolving power of a compound microscope depend? 29. Define refractive index of a transparent medium. A ray of light passes through a triangular prism. Plot a graph showing the variation of the angle of deviation with the angle of incidence. 30. Define the term linearly polarized light. When does the intensity of transmitted light become maximum, when a polaroid sheet is rotated between two crossed polaroids? Short Answer Type Questions-II [3 marks each] 31. Draw a labelled ray diagram of a reflecting telescope. Mention its two advantages over the refracting telescope. 32. You are given three lenses having powers P and Apertures A as follow : P1 = 6D, A1 = 3cm P2 = 3D, A2 = 15cm P3 = 12D, A3 = 1.5cm 33. What is an unpolarized light and polarized light? Under what condition does a beam of light reflected by a transparent medium become plane polarized? Use this condition to establish a relation between the angle of incidence and the refractive index of the transparent medium. 34. In a single slit diffraction experiment, the width of the slit is made double the original width. How does this affect the size and intensity of the central diffraction band? Draw a plot of the intensity distribution. 35. State Mauls law and draw a graph showing the variation of intensity of polarized light transmitted by an analyzer. A polarizer and an analyzer are so oriented that intensity of transmitted light is maximum. If the analyzer is rotated through 600, what fraction of the maximum light is transmitted? 36. (i)derive the mirror formula which gives the relation between f, v and u. (ii)a convex lens of refractive index n1 is held in a medium of refractive index n2. Trace the path of refracted rays of a parallel beam of light incident on the lens when (i) n2>n1 and (ii) ) n2=n1 37. A convex lens of focal length f1 is kept in contact with a concave lens of focal length f2. Find the focal length of the combination. 38. A parallel beam of light of 600nm falls on a narrow slit and the resulting diffraction pattern is observed on a screen 1.2 m away. It is observed that the first minimum is at a distance of 3mm away from the centre of the screen. Calculate the width of the slit.

28 39. A parallel beam of light of 500nm falls on a narrow slit and the resulting diffraction pattern is observed on a screen 1m away. It is observed that the first minimum is at a distance of 2.5mm away from the centre of the screen. Calculate the width of the slit. 40. Draw a labelled ray diagram of a reflecting type telescope. Write its any two advantage over refracting type telescope. 41. State Huygens s principle. Show, with the help of a suitable diagram, how this principle is used to obtain the diffraction pattern by a single slit. a. What is meant by normal adjustment of an astronomical telescope? Trace the path of rays from a distant object through a refracting astronomical telescope in normal adjustment. Derive an expression for its magnifying power and length of tube in this position. 42. How would the length of the day be affected if there were no atmosphere around the earth? Explain your answer with the help of a diagram. 43. With the help of Huygens principle explain laws of refraction. And draw refracted wavefront when a plane wavefront incident on a concave mirror. 44. A parallel beam of light of 500 nm falls on a narrow slit and the resulting diffraction pattern is observed on a screen 1 m away. It is observed that the first minimum is at a distance of 2.5 mm from the centre of the screen. Calculate the width of the slit. 45. Draw the ray diagram of compound microscope in normal adjustment and hence find the magnifying power of it in normal adjustment. How does its magnifying power and resolving power change on (i) increasing the focal lengths of the two lenses (ii) using the light of higher wavelength 46. Find a relation for resolving power of a microscope. How is the resolving power of a microscope affected when, (i) The wavelength of illuminating radiations is decreased? (ii) The diameter of the objective lens is decreased? Justify your answer.

29 47. A right angled crown glass prism with critical angle 410 is placed before an object PQ, in two positions as shown in the figure(i) and (ii).trace the paths of the rays from P and Q passing through the prisms in the two cases. 48. A compound microscope with a objective of 1.0 cm focal length and an eyepiece of 2.0 cm focal length has a tube of length of 20 cm. Calculate the magnifying power of the microscope, if the final image is formed at the near point of the eye. Long Answer Type Questions [5 marks each] 49. Draw the graph showing the variation of angle of deviation with angle of incidence for a monochromatic ray of light passing through a prism of angle A. Deduce an expression for its refractive index in terms angle of minimum deviation and angle of prism? a. A right angled isosceles glass prism is made from glass of refractive index 1.5. Show that a ray of light incident normally on: (i)one of the equal sides of this prism is deviated through 90 0 ii) The hypotenuse of this prism is deviated through What are coherent sources of light? State two conditions for two light sources to be coherent. Derive a mathematical expression for fringe width if interference fringe obtained in Young s Double Slit Experiment with the help of a suitable diagram. 51. Explain total internal reflection. A light beam is incident on the boundary between two transparent media. At a particular angle of incidence the reflected ray is perpendicular to the refracted ray. Obtain the expression this angle of incidence. Does this expression depend on the wavelength of light used?

30 52. State Huygens principle for reflection of plane wave front at a plane reflection surface. Construct the corresponding reflected wave front. Using this diagram prove the laws of reflection. 53. A spherical surface, of radius of curvature R, and of refractive index µ2, is placed in a medium of refractive index µ1 where µ1 < µ2. The surface produces a real image of an object kept in front of it. Using appropriate assumptions and sign conventions, derive a relationship between the object distance, image distance, R, µ1 and µ2. Under what conditions this surface diverges a ray incident on it? For the same angle of incidence the angle of refraction in three different media A, B and C are 15º, 25º and 35º respectively. In which medium the velocity of light is minimum? 54. Two lenses of power 10 D and -5D are placed in contact. a. Calculate the power of lens combination. b. Where should an object is held from the lenses, so as to obtain a virtual image of magnification (i) What is interference of light? Write two essential conditions for sustained interference pattern to be produced on the screen. What is the effect on interference pattern in Young s double slit experiment, when 1. screen is moved closer to the plane of slits, 2. Separation between two slits is increased? (ii).draw a graph showing the variation of intensity versus the position on the screen in Young s double slit experiment, when (a) (b) Both the slits are opened and One of the slits is closed. 56. A convex lens made up of glass of refractive index 1.5 is dipped, in turn, in: (i) medium A of refractive index 1.65 (ii) medium B of refractive index 1.33 Explain, giving reasons, whether it will behave as a converging lens or a diverging lens in each of these two media.