CURRENT ELECTRICITY LEVEL A QUESTIONS

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1 CURRENT ELECTRICITY LEVEL A QUESTIONS 1.Define electric current and give its SI unit. (1) 2. Define current density and give its SI unit. (1) 3. State Ohm s law. (1) 4. Derive an expression for resistivity..mention its SI unit. (2) 5.What is drift velocity? Derive an expression for the same. (2) 6. Obtain an expression for the conductance in terms of number density of electrons & average collision time. (2) 7. Define electron mobility. Give its SI unit.(1) 8. What are non-ohmic conductors? Give any one example. (1) 9. Define temperature coefficient of resistance & give its SI unit. (1) 10. Show graphically the temperature dependence of resistivity in i.) metals,ii.) alloys & iii. )semiconductors. (3) 11. Give expressions for the equivalent resistance in the series & parallel combination of three resistances. (1) 12. Distinguish between emf & terminal potential difference.(2) 13. Give the expression for the equivalent emf when cells are connected in series. (1) 14. Write the expression for the terminal voltage when two cells of emf E 1 & E 2 are connected in parallel. (1) 15. State Kirchoff s junction rule & loop rule. (2) 16. Explain the principle of Wheatstone bridge with the help of a circuit diagram.. (2) 17. What is the principle on which metre bridge works? With the help of a circuit diagram explain how an unknown resistance can be measured by using a metre bridge. (2)

2 18. Give the principle of potentiometer. (1) 19. Explain the procedure with the help of a circuit diagram for comparing the emfs of the two cells using potentiometer. (3) 20. Explain the procedure with the help of a circuit diagram for determining the internal resistance of a primary cell using potentiometer. (3) LEVEL B QUESTIONS 1. How can a current in a circuit be kept continuous? (1) 2. Why electric current is not a vector quantity? (1) 3. Is a wire carrying current charged? (1) 4. Name the metal which has the largest conductivity. (1) 5. Two wires of equal length, one of copper & the other of managing have same resistance. Which one is thicker? (1) 6. A copper wire of resistivity ρ is stretched to reduce its diameter to half. What will be its new resistivity? (1) 7. Why are copper wires used as connecting wires? (1) 8. What is the order of drift velocity? (1) 9. Though the drift velocity of electrons is very small, yet an electric bulb lights up almost instantly when switched on. Why? (2) 10. If a current of one ampere flows through a conductor,find the number of electrons passing through the wire in 1.6 seconds. (1) 11. Of metals & alloys,which has largest value of temperature coefficient of resistance? (1) 12.For a carbon resistor of 47kΩ write the sequence of colours on its rings. (1) 13. If the potential difference across a conductor is doubled,how will it affect the drift velocity of the electrons? (1) 14. Two electric bulbs A & B are marked 220V,60W and 220V,100W respectively. Which one of the two has greater resistance? (2)

3 15. The voltage V versus current I graph for a parallel & series combination of two metallic resistors is shown. Which graph shows the parallel combination? Justify your answer. (2) V A B 16. When n identical resistors,each of resistance R are put in series,effective resistance is X ohm & when they are connected in parallel the effective resistance is Y ohm. Obtain a relation connecting X,Y & R. (2) 17. A p.d V is applied across the ends of a conductor of length L & diameter D. How are the electric field E and the resistance R of the conductor are affected when: a.) V is halved b.) L is halved c.) D is doubled. (3) 18.A steady current flows through a metallic conductor of non uniform cross section. Which of these quantities is constant along the conductor? a.) current b.) current density c.) electric field d.) drift velocity. (2) 19. Three bulbs of rating 40,60 & 100 W are designed to work on 220V mains. Which bulb will glow most brightly if they are connected in series across the mains? (2) 20. Why do we prefer potentiometer for measuring emf of a cell rather than a voltmeter? (1) 21. Why should the emf of a driver cell in a potentiometer be more than the emf of a cell which is to be determined? (1) 22.When is a potentiometer said to be more sensitive?how can its sensitivity be increased? (2) 23. Why is it advised to obtain a null point in the middle of the metre bridge wire? (1) I

4 24. State Kirchoff s laws of an electrical network. Using Kirchoff s laws, calculate the potential difference across the 8 ohm resistor. 25. A metre bridge, the balance point is found to be at 39.5 cm from the end A, when the resistor Y is of 12.5 ohm. Determine the resistance of X. Why are the connections between resistors in a metre bridge made of thick copper strips? What happens if the galvanometer and cell are interchanged at the balance point of the bridge? Would the galvanometer show any current? LEVEL C QUESTIONS 1. What is meant by the sensitivity of a potentiometer? A battery E 1 of 4 V and a variable resistance R h are connected in series with the wire AB of the potentiometer. The length of the wire of the potentiometer is 1 metre. When a cell E 2 of e.m.f. 1.5 volt is connected between points A and C, no current flows through E 2 Length of AC = 60 cm. (i) Find the potential difference between the ends A and B of the potentiometer, (ii) Would the method work, if the battery E<sub.1 is replaced by a cell of e.m.f. of 1 V? (3)

5 2. The given graph shows the variation of resistance of mercury in the temperature range 0 < T < 4 K. Name the phenomenon shown by the graph. (1) 3. In the given network, find the values of the currents, I 1, I 2 and I 3. (3) 4. Find the current drawn from a cell of emf IV and internal resistance 2/3 connected to the network shown in the figure. E = 1v r = 2/3 5. A wire of resistance 4R is bent in the form of a circle. What is the effective resistance between the ends of the diameter? (1) 6.A given copper wire is stretched to reduce its diameter to half of its previous value.what is its new resistance? (2) 7. 4 cells of identical emf E, internal resistance r, are connected in series to a variable resistor. The following graph shows the variation of terminal voltage of the combination with the current output: (3)

6 (i) What is the emf of each cell used? (ii) For what current from the cells, does maximum power dissipation occur in the circuit? (iii) Calculate the internal resistance of each cell.

7 ATOMS & NUCLEI LEVEL A QUESTIONS 1. Name the experiment which is associated with the discovery of atomic nucleus. (1) 2. What will be the ratio of radii of two nuclei with mass numbers A1 & A2? (1) 3. What are isotopes? give one example. (1) 4. What are isobars? Give one example. (1) 5. What are isotones? Give one example. (1) 6. What is binding energy? (!) 7. Name some important characteristics of nuclear forces. (2) 8. What is the atomic & mass numbers of element X? (1) 0 n Hg 198 X + 1 H 1 9. Define radioactive decay constant. (1) 10. What is half life of a radioactive substance? (1) 11. What is average life of a radioactive substance? (1) 12. How is the half life of a radioactive substance related to its average life? (1) 13. Why do we use neutrons for causing nuclear reactions? (1) 14. Name the SI unit of radioactivity. (1) 15. Plot the graph between the binding energy per nucleon & the mass number. Hence explain nuclear fission & fusion based on this graph.(3) 16. What is radioactivity? Draw the radioactive decay curve. (2) 17. What is the SI unit of decay rate? (1) 18. Establish the relationship between decay constant & half life of a radioactive substance. (2) 19. Explain the origin of spectral lines. Obtain an expression for Rydberg s constant & write its value. (3) 20. Draw energy level diagram for hydrogen atom. (2) 21. State the limitations of the Bohr s theory. (2)

8 22. Draw a labelled diagram of experimental setup of Rutherford 's alpha particle scattering experiment. Write two important inferences drawn from this experiment.(2) 23.Name the parts of a nuclear reactor (2) 24.Write the functions of the following: i. fuel rods ii. Coolant iii. Moderator (3) LEVEL B QUESTIONS 1.The sequence of stepwise decays of a radioactive nucleus is If the nucleon number and atomic number for D2 are 176 and 71 respectively, what are the corresponding values of D and D3? Justify your answer in each case. (2) 2. The half life of a radioactive substance is 30 s.calculate i.)decay constant. Ii.) time taken by the sample to become one-fourth of its initial value. (2) 3. A neutron is absorbed by a nucleus with the subsequent emission of an alpha particle. (i) Write the corresponding nuclear reaction. (ii) Calculate the energy released, in MeV, in this reaction (3) 4. In the series of radioactive disintegration of first an alpha-particle and then a beta-particle is emitted. What is the atomic number and mass number of the new nucleus formed by these successive disintegrations (2) 5. A nucleus undergoes to give the nucleus Write down the equation. Calculate the kinetic energy of the electron emitted, assuming the mass of as u and that of as u. Rest mass of the electron may be ignored. (2) 6.State the radioactive disintegration law & deduce exponential law from it. (3)

9 LEVEL C QUESTIONS 1. The graph shows how the activity of a sample of radon.220 changes with time. Use the graph to determine its half-life. Calculate the value of decay constant of radon-220. (2) 2.The half life of a radioactive substance is 4 hours. a.) In how much time will 7/8 th of the material decay? B.)Tritium has a half life of 12.5 yearsagainst the beta decay. What fraction of the sample of tritium will remain undecayed in 25 years? (3) 3. Explain how radioactive nuclei can emit even though atomic nuclei do not contain these particles. Hence explain why the mass number of a radioactive nuclide does not change during Use the basic law of radioactive decay, to show that radioactive nuclei follow an exponential decay law. Hence obtain a formula, for the half-life of a radioactive nuclide, in terms of its disintegration constant. (5) 4.For scattering by an inverse square field (such as that produced by a charged nucleus in Rutherford s model)the relation between the impact parameter b & the scattering angle θ is given by b=(ze 2 cotθ/2) / (2πε 0 mv 2 ): a.)what is the scattering angle for b=0? b.)for a given impact parameter b, does the angle of deflection increase or decrease with the increase of energy? c.) what is the impact at which scattering angle is 90 0 for Z= 79 and initial energy = 10MeV

10 does? d.)why is it that the mass of the nucleus does not enter the formula above,but its charge e.)for a given energy of the projectile,does the scattering angle increase or decrease with the decrease in impact parameter? (5)

UNIT II CURRENT ELECTRICITY

UNIT II CURRENT ELECTRICITY UNIT II CUENT ELECTICITY Weightage : 07 Marks Electric current; flow of electric charges in a metllic conductor, drift velocity, mobility and their relation with electric current. Ohm s law electrical