INTERNATIONAL INDIAN SCHOOL, RIYADH XI XII BOYS SECTION 2018-19 GRADE: XII WORKSHEET SUBJECT: PHYSICS 1 ELECTRIC FIELDS AND CHARGES 1. What is the force between two small charged spheres having charges of 2 10-7 C and 3 10-7 C placed 30 cm apart in air? 2. The electrostatic force on a small sphere of charge 0.4µC due to another small sphere of charge -0.8µC in air is 0.2N. (a) What is the distance between the two spheres? (b) What is the force on the second due to the first? 3. A spherical Gaussian surface encloses a charge of 8.85 10-12 C. (a) Calculate the electric flux passing through the surface? (b) How would the flux change if the radius of the Gaussian surface is doubled and why? 4. Two large parallel thin metallic plates are placed close to each other. The plates have surface charge densities of opposite signs and of magnitude 20 10-12 C/m 2. Calculate the electric field intensity (i) in the outer region of the plates and (ii) in the interior region between the plates. 5. State Gauss s law in electrostatics. Use this law to derive the expression for the electric field due to a uniformly charged infinite thin plane sheet. 6. Define term electric dipole moment. Is it a scalar or vector? 7. Why must electrostatic field be normal to the surface at every point of a charged conductor? 8. A charge q is placed at the centre of a cube. What is the electric flux passing through a single face of the cube? 9. Define electric flux. 10. Figure shows three point charges, +2q, -q and +3q. Two charges +2q and -q are enclosed within a surface S. What is the flux due to this configuration through the surface S? S +3q 2 ELECTRIC POTENTIALS AND CAPACITANCE 1. Explain the underlying principle of working of a parallel plate capacitor. If two similar plates, each of area A having surface charge densities +σ and σ are separated by a distance d in air, write expressions for (a) the electric field at points between the two plates. (b) the potential difference between the plates. (c) the capacitance of the capacitor so formed. 2. (i) Can two equipotential surfaces intersect each other? Give reasons. (ii) Two charges q and +q are located at points A (0, 0, -a) and B (0, 0, +a) respectively. How much work is done in moving a test charge from point P (7, 0, 0) to Q (-3, 0, 0)? 3. What is the electrostatic potential due to an electric dipole at an equatorial point?
4. The equivalent capacitance of the combination between A and B in the given figure is 4µF. 20µF C A B (i) Calculate the capacitance of the capacitor C. (ii) Calculate the charge on each capacitor if a 12V battery is connected across terminals A and B. 5. Two charges 5 10 8 C and 3 10 8 C are located 16 cm apart. At what point(s) on the line joining the two charges is the electric potential zero? Take the potential at infinity to be zero. 6. A regular hexagon of side 10 cm has a charge 5 5C at each of its vertices. Calculate the potential at the centre of the hexagon. 7. A parallel plate capacitor with air between the plates has a capacitance of 8 pf (1pF = 10 12 F). What will be the capacitance if the distance between the plates is reduced by half, and the space between them is filled with a substance of dielectric constant 6? 8. A 12 pf capacitor is connected to a 50V battery. How much electrostatic energy is stored in the capacitor? 9. What is meant by equipotential surface? 10. Define electrostatic potential. 3 CURRENT ELECTRICITY 1. Calculate the value of the current drawn from a 5V battery in the circuit as shown. 2. A 10 v battery of negligible internal resistance is connected across a 200 V battery and a resistance of 38Ω as shown the figure. Find the value of the current in the circuit. 3. The number density of conduction electrons in a copper conductor is 8.5 x10 28 m -3. How long an electron take to drift from one end of a wire 3m long, to its other end? A = 2x10-6 m 2 and it is carrying a current of 3 A.
4. A silver wire has a resistance of 2.1 Ω at 27.5 0 C and a resistance of 2.7 Ω at 100 0 C. Determine the temperature coefficient of resistivity of silver. 5. A steady current flows in a metallic conductor of non uniform crossection. Which of the following quantities is constant along the conductor: current, current density, drift velocity.? 6. Which of the two has greater resistance : 1kW electric heater or a 100 W tungsten bulb, both marked 230 V. 7. A wire of resistivity ρ is stretched to double its length what will be its new resistivity? 8. A carbon resistor is marked in colour bands of red, black, orange and silver. What is the resistance and tolerance value of the resistor? 9. Why do we prefer a potentiometer to measure the emf of a cell rather than a voltmeter? 10. Define current sensitivity of a galvanometer. Write its S.I unit 4 MOVING CHARGES AND MAGNETISM 1. A long straight wire in the horizontal plane carries a current of 50A in north to south direction. Give the magnitude and direction of B at a point 2.5m east of the wire. 2. What is the magnitude of magnetic force per unit length on a wire carrying a current of 8A and making an angle of 30º with the direction of a uniform magnetic field of 0.15T? 3. A galvanometer coil has a resistance of 12Ω and the metre shows full scale deflection for a current of 3mA. How will you convert the metre into a voltmeter of range 0 to 18V? 4. State Ampere s circuital law. 5. What is the direction of the force acting on a charged particle q, moving with a velocity v in a uniform magnetic field B? 6. Magnetic field lines can be entirely confined within the core of a toroid, but not within a straight solenoid, why? 7. A narrow beam of protons and deuterons, each having the same momentum, enters region of uniform magnetic field directed perpendicular to their direction of momentum. What would be the ratio of the radii of the circular paths described by them? 8. Write the expression for Lorentz magnetic force on a particle of charge q moving with velocity v in a magnetic field B. Show that no work is done by this force on the charged particle. 9. State Biot-Savart law. 10. Draw a labeled diagram of Moving coil galvanometer. 5. MAGNETISM AND MATTER 1. 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 that place? 2. What is the unit and direction of magnetic dipole moment? 3. What is the basic difference between magnetic lines of force and electric lines of force? 4. Why two magnetic lines of force do not cross each other? 5. Horizontal component and vertical component of earth s magnetic field at a place are equal. What is the angle of dip at this place?
6. What happens when a diamagnetic substance is placed in a varying magnetic field? 7. Soft iron is used to make electromagnets. Why? 8. Calculate the work done in rotating a bar magnet of magnetic moment 3 J/T through an angle of 60 0 from its position along a magnetic field of strength 0.34 x 10-2 T. 9. An electron in an atom revolves around the nucleus in an orbit of radius 0.5 A 0.Calculate the equivalent magnetic moment if the frequency of revolution of electron is 10 10 M Hz. 10. A magnetized needle of magnetic moment 4.8x10-2 T Is placed at 30 0 with the direction of uniform magnetic field of magnitude 3x10-2 T. Calculate the torque acting on the dipole. 6. ELECTROMAGNETIC INDUCTION 1. A metallic wire 1m in length is moving normally across a field of 0.1 T with a speed of 5 m/s. Find the emf between the ends of the wire. 2. The magnetic flux threading a coil changes from 12x10-3 Wb to 6 x 10-3 Wb in 0.01s. Calculate the induced emf. 3. A wire cuts across a flux of 0.2x10-2 Weber in 0.12 seconds. What is the value in the wire? 4. State Lenze s law. Does it violate law of conservation of energy? Explain? 5. What are eddy currents? Name any two of its applications. 6. How can eddy currents be reduced? 7. Derive an expression for the energy stored in an inductor. 8. State the factors on which the induced emf in a coil rotating in a uniform magnetic field depends. 9. On what factors does the magnitude of the emf induced in the circuit due to magnetic flux depend? 10. Define the term self inductance of the coil. Give its S.I unit. 7 ALTERNATING CURRENTS 1. (a) The peak voltage of an ac supply is 300 V. What is the rms voltage? (a) The rms value of current in an ac circuit is 10 A. What is the peak current? 2. Define Q-factor. 3. A series LCR circuit with R=20Ω, L=1.5H and C=35µF is connected to a variable frequency 200V ac supply. When the frequency of the supply equals the natural frequency of the circuit, what is the average power transferred to the circuit in one complete cycle. 4. Obtain the resonant frequency wr of a series LCR circuit with L=2.0H, C=32µF and R=10Ω.What is the Q-factor (Q) of this circuit? 5. Calculate the (i) impedance of the given circuit. C R 40V 6. Explain the working of a transformer. 30V 2A Vrms
7. Calculate the quality factor of a series LCR circuit with L=2.0 H, C= 2µF and R=10Ω.Mention the significance of quality factor in LCR circuit. 8. Draw phasor diagram for series LCR circuit. 9. A series LCR circuit with L = 0.12 H, C = 480 nf, R = 23 Ω is connected to a 230 V variable frequency supply. (a) What is the source frequency for which current amplitude is maximum? Obtain this maximum value. (b) What is the source frequency for which average power absorbed by the circuit is maximum? Obtain the value of this maximum power. 10. A charged 30µF capacitor having initial charge 6mC is connected to a 27mH inductor. (a) What is the angular frequency of free oscillations of the circuit? (b)what is the total energy stored in the circuit initially? What is the total energy at later time? 8 ELECTROMAGNETIC WAVES 1. A plane electromagnetic wave travels in vacuum along z direction. What can you say about the directions of electric and magnetic field vectors? If the frequency of the wave is 30 MHz, what is its wave length. 2. Write the order of frequency range and one use of each of the following electromagnetic radiations : a) microwaves b) ultraviolet rays. 3. What do electromagnetic waves consists of? Explain on what factors does its velocity in vacuum depend? 4. Give two characteristics of electromagnetic waves. Write the expression for velocity of electromagnetic wave in terms of permittivity and permeability of the medium 5. What is meant by transverse nature of electromagnetic waves? 6. Draw a diagram showing the propagation of an electromagnetic wave along x direction, indicating the directions of oscillating electric and magnetic fields associated with it? 7. Long distance radio broadcast use short wave bands why? 8. It is necessary to use satellite for long distance TV transmission why? 9. Name the part of electromagnetic spectrum of wave length 10-2 m and mention its one application 10. Why are microwaves used in RADAR? 9 RAY OPTICS 1. Write the relationship between angle of incidence, angle of prism and angle of minimum deviation for a triangular prism. 2. How does the power of a convex lens vary, if the incident red light is replaced by violet light? 3. Define power of a lens. Write its SI unit. 4. Why does the bluish color predominate in a clear sky? 5. An object is placed at the principal focus of a convex lens of focal length f. Where will its image be formed?
6. List some advantages of a reflecting telescope. 7. Derive thin lens formula? 8. State the conditions for total internal reflection to occur. 9. Draw a labeled ray diagram showing the formation of image in a compound microscope. Write the expression for its magnifying power. 10. Draw a labeled ray diagram of a reflecting telescope. 10 WAVE OPTICS 11. In Young s double-slit experiment, the slits are separated by 0.28mm and the screen is placed 1.4m away.the distance between the central bright fringe and the fourth bright fringe is measured to be 1.2m.Determine the wavelength of light used in the experiment. 12. If the angle between the pass axis of polariser and the analyser is 45 0, write the ratio of the intensities of original light and the transmitted light after passing through the analyser. 13. Light of wavelength 5000A 0 falls on a plane reflecting surface. What are the wavelength and frequency of the reflected light? For what angle of incidence is the reflected ray normal to the incident ray? 14. A parallel beam of light of wavelength 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 from the centre of the screen. Find the width of the slit. 15. Two sources of intensity I and 4I are used in an interference experiment. Find the intensity at a point where the waves from the two sources superimpose with a phase difference of (i) zero (ii) π/2 (iii) π. 16. What is diffraction of light? Draw a graph showing the variation of intensity with angle in a single slit diffraction experiment. Write one feature which distinguishes the observed pattern from the double-slit interference pattern. How would the diffraction pattern of a single slit be affected when: (a) the width of the slit is increased? (b) the monochromatic source of light is replaced by a source of white light? 17. How is resolving power of a microscope affected when (i) wavelength of illuminating radiations is increased (ii) the diameter of objective lens is decreased? Justify. 18. Unpolarised light is incident on a plane surface of glass of refractive index µ at angle i. If the reflected light gets totally polarized, write the relation between the angle i and refractive index µ. 19. Distinguish between unpolarised and plane polarised light. 20. What does the statement, natural light emitted from the sun is unpolarised mean in terms of the direction of electric vector? 11 DUAL NATURE OF MATTER AND RADIATION 1. Write two characteristic features observed in photoelectric effect which support the photon picture of electromagnetic radiation.
2. Define work function for a given metallic surface. 3. The wavelength of electromagnetic radiation is doubled. How will the energy of a photon change? 4. What is the stopping potential applied to a photocell if the maximum kinetic energy of a photoelectron is 5eV? 5. If the intensity of radiation in a photocell is increased how does the stopping potential vary? 6. Write the expression for the de Broglie wavelength associated with a charged particle having charge q and mass m, when it is accelerated by a potential V. 7. Show the variation of photocurrent with collector plate potential for different frequencies but same intensities of incident radiation. 8. Write Einstein s photoelectric equation. 9. Work function of sodium is 2.3 ev. Does sodium show photoelectric emission for light of wavelength 6800 A 0? 10. How does the maximum kinetic energy of electrons emitted vary with the work function of the metal? 12 ATOMS 1. The short wavelength limit for the Lyman series of the hydrogen is 913.4A. calculate the short wavelength limit for Balmer series for hydrogen spectrum. 2. Using Rutherford model of atom, derive the expression for the total energy of the electron in hydrogen atom. What is the significance of total negative energy possessed by the electron? 3. Using Bohr postulates of the atomic model, derive the expression for Bohr s radius. 4. Using de Broglie s hypothesis, explain with the help of a suitable diagram, Bohr s postulate of quantization of energy levels in a hydrogen atom 5. What is the maximum number of special line emitted by a hydrogen atom when it is in the fourth excited state? 6. In the first excited state of hydrogen atom, its radius is found to be 21.2x10-11 m. Calculate its Bohr radius in the ground state. Also calculate the total energy of the atom in the second excited state. 7. Define ionisation energy. What is its value for a hydrogen atom? 8. The ground state energy of hydrogen atom is 13.6 ev. What is the potential energy of an electron in the 3 rd excited state? 9. The ground state energy of hydrogen atom is 13.6 ev. What is the kinetic energy of an electron in the 2 nd excited state? 10. The short wavelength limit for the Lyman series of the hydrogen is 913.4 A Calculate the short wavelength limit for Balmer series of hydrogen spectrum 13 NUCLEI 1. (i) Define the activity of a radioactive nucleus and state its SI unit.
(ii) Tritium has a half-life of 12.5 years against β-decay. What fraction of a sample of pure tritium will remain undecayed after 37.5 years? 2. A nucleus with A=235 splits into two new nuclei whose mass number are the ratio of 2:1. Find the radii of the new nuclei. 3. You are given two nuclei 3X 7 and 3Y 4. Explain giving reasons, as to which one of the two nuclei is likely to be more stable? 4. State the law of radioactive decay. 5. Obtain the binding energy of the nuclei 26Fe 56 and 83Bi 209 in units of Mev from the following data: m (26Fe 56 )=55.934939u; m (83Bi 209 ) =208.980388u. Which nucleus has greater binding energy per nucleon? Take 1u=931.5 Mev. 6. What are the properties of α, β and γ rays? 7. A radioactive isotope has a half- life of T years. How long will it take the activity to reduce to (a) 3.125% (b) 1% of its original value? 8. A radioactive nucleus A undergoes a series of decays according to the following scheme: A α A1 β A2 α A3 γ A4 The mass number and atomic number of A are 180 and 72 respectively. What are these numbers for A4? 9. Plot a graph showing the variation of activity of a given radioactive sample with time. 10. Differentiate between nuclear fission and nuclear fusion. 14 SEMICONDUCTORS 1. Draw a circuit diagram of a full wave rectifier. Explain its working and draw input and output wave forms. 2. What is Zener diode? How Zener diode is used as a voltage regulator? 3. Draw a simple circuit of a CE transistor amplifier. Explain its working. Find voltage gain, and current gain. What is the significance of the negative sign in the expression for the voltage gain? 4. Identify the equivalent gate for the following circuit and write its truth table 5. Describe briefly with the help of a circuit diagram, the paths of current carriers in an n-p-n transistor with emitter base junction forward biased and base- collector junction reverse biased. 6. Explain briefly, with the help of circuit diagram, how V-I characteristics of a
p-n junction diode are obtained in 1 ) forward bias, and 2 ) reverse bias. 7. Explain with the help of a circuit diagram the working of a photo diode. 8. Draw the energy band diagram of n- type and p type semiconductor at temperature, T > 0K 9. How does the width of the depletion region of a p- n junction vary, if the reverse bias applied to it vary? 10. Explain the function of base region of a transistor. Why is this region made thin and lightly doped? 15 COMMUNICATION SYSTEMS 1. Is it necessary for a transmitting antenna to be at the same height as that of the receiving antenna for line of sight communication? A TV transmitting antenna is 81m tall. How much service area can it cover if the receiving antenna is at the ground level? 2. Distinguish between frequency modulation and amplitude modulation. Why is an FM signal less susceptible to noise than AM signal? 3. A radio can tune to any station in the 7.5 MHz band. What is the corresponding wavelength band? 4. Give reasons for the following: (i) For ground wave transmission, size of antenna (i) should be comparable to wavelength of signal i.e., λ/4. (ii) Audio signals, converted into an em wave, are not directly transmitted as such. (iii) The amplitude of modulating signal is kept less than the amplitude of carrier wave. 5. A TV has a height of 71m. What is the maximum distance upto which TV transmission can be received? Given that the radius of earth=6 10 6 m. 6. Draw a plot of the variation of amplitude versus frequency for an amplitude modulated wave. Define modulation index. 7. What should be the length of dipole antenna for a carrier wave of frequency 6 10 8 Hz? 8. Draw a block diagram showing the important components in a communication system. What is the function of a transducer? 9. What is the purpose of modulating a signal in transmission? 10. Define sky wave propagation. Prepared by Mrs. Shani Haneesh Mrs. Manju (XI XII BOYS SECTION)