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Question Bank No: 2

1. Work done in carrying a charge $Q^{1}$ around a circle of radius 'r' with a charge Q at the centre is

a)		$Q / 4 π ɛ_{0} r$
b)		$Q^{1} Q / 4 π ɛ_{0} r$
c)		Zero
d)		${QQ}^{1} / 2 r$

2. Ampere-hour is the unit of

a)		Charge
b)		strength of electric current
c)		energy
d)		work

3. The electric potential energy between two protons of a uranium atom if the distance between the two protons is $6 \times 10^{- 15} m$ and charge on each proton is $1.6 \times 10^{- 19} C$ is

a)		$3.84 \times 10^{- 14} J$
b)		$7.68 \times 10^{- 14} J$
c)		$1.85 \times 10^{- 14} J$
d)		Zero

4. A Charge Q is placed at the centre of a Cube. The electric flux through on of the faces of the cube is

a)		$Q / ɛ_{0}$
b)		$Q / 2 ɛ_{0}$
c)		$2 Q / ɛ_{0}$
d)		$Q / 6 ɛ_{0}$

5. The electric field acting on an electron in a hydrogen atom due to the proton in the nucleus, if the distance between the proton and electron is $5.3 \times 10^{- 11} m$ in N/C is

a)		$5.1 \times 10^{11}$
b)		$5.1 \times 10^{- 11}$
c)		$1.6 \times 10^{- 19}$
d)		$1.6 \times 10^{19}$

6. The electric field acting on a proton so that proton remains stationary in space is $(m_{e} = 1.67 \times 10^{- 27})$

a)		$1.6 \times 10^{- 19} N / C$
b)		$1.02 \times 10^{- 6} N / C$
c)		$5 \times 10^{- 7} N / C$
d)		$1.02 \times 10^{- 7} N / C$

7. Two charges +20 $μ$ C and -20 $μ$ C are placed 1 cm apart. The electric field at a point on the axial line at a distance of 20 cm from the centre of the dipole in N/C is

a)		$4.5 \times 10^{5}$
b)		$9 \times 10^{5}$
c)		$4.5 \times 10^{6}$
d)		$2.25 \times 10^{5}$

8. Two fixed point charges +4e and +e units are separated by a distance 'a'. Where should a third point charge be placed for it to be in equilibrium?

a)		2a/3 from +4e
b)		2a/3 from +e
c)		a/3 from +4e
d)		a/3 from +e

9. A body has a charge of -1C. The number of excess electrons on the body is

a)		${6.25 \times 10}^{18}$
b)		${6.25 \times 10}^{13}$
c)		${1.6 \times 10}^{19}$
d)		${16 \times 10}^{13}$

10. At the eight corners of a cube of side 'a' cm are situated equal charges of 'q' units each. What is the field at the centre of cube?

a)		3a/2
b)		$\sqrt{3} a / 2$
c)		3q/2
d)		zero

11. A charge 'q' is placed at the centre of the line joining two equal charges 'Q'. The system of the three charges will be in equilibrium if 'q' is equal to

a)		-Q/2
b)		-Q/4
c)		+Q/4
d)		+Q/4

12. Two charges $+ 10^{- 15} C$ each are kept 10 cm apart. The electric field at a point midway between them in N/C is

a)		zero
b)		$10 \times 10^{- 13}$
c)		$9 \times 10^{- 9}$
d)		$9 \times 10^{- 2}$

13. The potential difference between to parallel plates is 100 V and the electric field at a point between them is $10^{4}$ V/m. The distance between the plates is

a)		2 cm
b)		3 cm
c)		4 cm
d)		1 cm

14. The electric potential energy of electron proton system of hydrogen atom in eV, if the radius of the electron orbit is $5.29 \times 10^{- 11} m$ is

a)		-22.27
b)		+27.22
c)		-27.22
d)		+22.27

15. A condenser of capacitance 8 $μ$ F is charged to a potential of 1000V. The energy stored in the condenser in joules is

a)		2
b)		3
c)		1.5
d)		4

16. A parallel plate capacitor has circular plates of radius 8 cm and plate seperation 1 mm. The capacitance of the capacitor will be

a)		178pF
b)		356pF
c)		89pF
d)		100pF

17. 27 million small drops each of radius 1 mm and having charge of $10^{- 10} C$ , coalesce to form a bigger drop. The potential of the bigger drop is

a)		$8 \times 10^{6} V$
b)		$18 \times 10^{7} V$
c)		$81 \times 10^{7} V$
d)		$18 \times 10^{6} V$

18. The electric field inside a spherical shell of uniform charge density is

a)		zero
b)		uniform
c)		non uniform
d)		proportional to distance from the centre

19. An air parallel plate capacitor has capacitance C. When a medium of relative permittivity K is introduced between the plates, the capacitance is

a)		C+K
b)		C-K
c)		CK
d)		C/K

20. A parallel plate air capacitor has a capacitance 4 $μ$ F. When it is immersed in a liquid of relative permittivity $ɛ_{r},$ its capacitance will be 9 $μ$ F. The value of $ɛ_{r}$ is

a)		2
b)		2.5
c)		4/9
d)		9/4

21. Two small spheres carry charges of 2 $μ$ C and 5 $μ$ C respectively. The charges are 0.2m apart. The electric potential at the midpoint of the line joining the two charges is

a)		$6.3 \times 10^{5} V$
b)		$3.2 \times 10^{5} V$
c)		$1.2 \times 10^{5} V$
d)		zero

22. Two parallel plates ate maintained at a potential difference of $10^{3}$ V and are at a distance of 1 cm. The electric field at a point in between the plates is

a)		100 V/m
b)		1000 V/m
c)		$10^{7}$ V/ $10^{7}$ V/m
d)		$10^{5}$ V/ $10^{5}$ V/ $10^{5}$ V/ $10^{5}$ V/m

23. A charge is distributed over two electronic hollow spheres having radii 'R' and 'r' respectively, where R>r. such that the surface densities are equal. What will be the potential at the common centre?

a)		$σ (R - r) / ɛ_{0}$
b)		$σ R / ɛ_{0}$
c)		$σ (R \times r) / ɛ_{0}$
d)		$σ (R + r) / ɛ_{0}$

24. The potential energy of two equal positive charges 1 $μ$ C each held 1 m apart in air is

a)		1J
b)		1eV
c)		$9 \times 10^{- 3} J$
d)		zero

25. Which of the following statements is not true for an equipotential surface?

a)		The P.D between any two points on the surface is zero
b)		The electric field is always at right angles to the surface
c)		No work is done to move a chrge along a surface
d)		Equipotential surface are always spherical

26. A parallel plate capacitor has charge Q on it. The electric field in the space between the plates is E. The magnitutde of force on each plate must be

a)		QE
b)		QE/2
c)		Q/E
d)		2QE

27. During the process of induction some of the charges of the inducing body is

a)		lost
b)		gained
c)		first gained and then lost
d)		neither lost nor gained

28. Three charges 2q, -q, q are located at the vertices of an equilateral triangle. At the circumcentre

a)		the filed is non-zero but the potential is zero
b)		the field is zero but the potential is not zero
c)		both the field and potential are zero
d)		both field and potential are non-zero

29. One electron volt of energy is

a)		$1.6 \times 10^{- 13} J$
b)		$1.6 \times 10^{- 19} J$
c)		$4.8 \times 10^{- 12} J$
d)		$9 \times 10^{9} J$

30. The radius of earth is approximately 6400km. Its capacity in microfarad is

a)		6400 $μ$ F
b)		711 $μ$ F
c)		0.06 $μ$ F
d)		71.1 $μ$ F

31. The drift velocity of electrons in a metal of area of cross section $10^{- 5} m^{2}$ for a current of 20A in m/s is (Assume that $8.4 \times 10^{28}$ electrons / $m^{3}$ )

a)		$1.5 \times 10^{- 4}$
b)		$3 \times 10^{- 4}$
c)		$3 \times 10^{8}$
d)		$3 \times 10^{- 8}$

32. $10^{20}$ electrons each having a charge $1.6 \times 10^{- 19}$ C pass from a point X towards point Y in 0. What is the current and direction

a)		1600 A from Y to X
b)		160 A from X to Y
c)		16 A from Y to X
d)		160 A from Y to X