Untitled Document

Question Bank No: 1

1. Three charges +4q, Q and q are placed in a straight line of length l at points 0, $l / 2$ respectively. What should be Q is order to make the net force on q to zero?

a)		-q
b)		-2q
c)		-q/2
d)		+q

2. A hollow metallic sphere is placed in a region permeated by a uniform electric field which is directed upward. Which statement is correct concerning the electric field in the interior of the sphere?

a)		The field is zero everywhere in the interior
b)		The field is directed upward
c)		The field is directed downward
d)		The field is zero only at the exact centre

3. An electric field of force in the x-y plane is given by the equation $x^{2} + y^{2} = 1$ . A particle with unit positive charge initially at rest at x = 1, y = 0 with x - y plane

a)		will not move at all
b)		will move along a straight line
c)		will move along the circular line of force
d)		move in an elliptical orbit

4. Two particles of masses m and 2m with charges q and 2q are placed in a uniform elecric field E and allowed to move for the same time. The ratio of their kinetic energies will be

a)		2 : 1
b)		1 : 2
c)		4 : 1
d)		1 : 4

5. The earth has an electric charge that causes an electric field near its surface of the order of ${100 Vm}^{- 1}$ . What is the surface density of charge on the earth. Assume the earth to be a conducting sphere

a)		${8.85 \times 10}^{- 12}$
b)		${8.85 \times 10}^{- 8}$
c)		${8.85 \times 10}^{- 10}$
d)		${8.85 \times 10}^{10}$

6. A given charge situated at a certain distance from an electric diople in the end -on position experiences a force F. If the distance of the charge is doubled the force acting on the charge will be

a)		2F
b)		F/2
c)		F/4
d)		F/8

7. Two fixed charges +4q and +q are placed at a distance r apart. At what point between them a charge +q be placed so that it is in equilibrium

a)		r/2 from +4q
b)		$\frac{2}{3} r$ from 4q
c)		$\frac{r}{3}$ from 4q
d)		$\frac{r}{4}$ from + 4q

8. A charge q is placed at the midpoint of the line joining two equal charge +Q. Find the nature and magnitude of the charges so that the system is in equilibrium

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

9. An electric dipole of moment $\vec{P}$ is placed in an electric field $\vec{E}$ with its axis in the direction of the field. It is turned through $180^{\circ}$ . The work done is

a)		PE
b)		2PE
c)		zero
d)		-2PE

10. If the force between two charged particles is to be left unchanged even though the charge on one of the objects is halved, keeping the other the same, the original distance of seperation d should be changed to

a)		2d
b)		$\sqrt{2} d$
c)		$\frac{d}{\sqrt{2}}$
d)		$\sqrt{d / 2}$

11. The insulation property of air breaks down at intensity of electric field $3 \times 10^{6} {Vm}^{- 1}$ . The maximum charge that can be given to a sphere of diametre 5m is about

a)		$2 \times 10^{- 2} C$
b)		$2 \times 10^{- 3} C$
c)		$2 \times 10^{- 4} C$
d)		$2 \times 10^{- 5} C$

12. A proton of mass m = 1.6 $\times 10^{- 27}$ kg on entering a vertical electric field E is balanced. The electric field strength is

a)		$10^{- 9} {Vm}^{- 1}$
b)		$10^{- 7} {Vm}^{- 1}$
c)		$10^{7} {Vm}^{- 1}$
d)		$10^{- 8} {Vm}^{- 1}$

13. The dimensions of $\in_{0}$ is

a)		$M^{3} L^{- 2} T^{3} I^{3}$
b)		$M^{0} L^{0} T I^{- 2}$
c)		$M^{- 1} L^{- 3} T^{3} I^{2}$
d)		$M^{- 1} L^{- 3} T^{4} I^{2}$

14. The mathematical form of Gauss' theorem in electrostatic is

a)		$∲ \vec{E} . \vec{d} s = \frac{\sum q}{4 π \in_{0}}$
b)		$∲$ $\vec{E} . \vec{d} s = \frac{1}{\in_{0}} \int d q$
c)		$∲ \vec{E} \times \vec{d} s = \in_{0} \int d q$
d)		$∲ E . d s = \in_{0} \int d q$

15. An electric field can deflect

a)		X-rays
b)		$α$ -particles
c)		neutrons
d)		$γ$ -rays

16. The value of electric charge on any object cannot be less than

a)		${4.8 \times 10}^{- 19} C$
b)		1C
c)		${3.2 \times 10}^{- 19} C$
d)		${1.6 \times 10}^{- 19} C$

17. The unit of electric field is

a)		volt $\times$ metre
b)		volt / Joule
c)		volt $\times$ Joule
d)		volt / metre

18. When the distance between two charged particles is halved the force between them becomes

a)		one-fourth
b)		one half
c)		double
d)		four times

19. A rod of insulating material is given a positive charge by rubbing it with a piece of fabric and the fabric is then tested for electric charges. You would expect the fabric to have

a)		a positive charge equal to that on the rod
b)		negative charge equal to that on the rod
c)		a positive charge less than that of the rod
d)		a negative charge greater than that of the rod

20. The field due to an electric dipole on the axial line is proportional to

a)		$r^{2}$
b)		$\frac{1}{r^{2}}$
c)		$r^{3}$
d)		$\frac{1}{r^{3}}$

21. An electric dipole placed in a uniform magnetic field experiences

a)		a force as well as torque
b)		no force but a torque
c)		a force but no torque
d)		neither force nor torque

22. The ratio of the force between two small point charges in air and in a medium of dielectric constant k is

a)		K : 1
b)		1 : K
c)		$K^{2}$ : 1
d)		$\sqrt{k}$ : 1

23. Equal charges each of two coulomb are placed at points x = 0,2,4,8 cm on the x-axis. The force experienced by the charge at x = 2cm

a)		15 N
b)		5 N
c)		zero
d)		10 N

24. Insulated copper spheres of radii 10 cm and 15 cm and having equal charges are connected by a copper wire and seperated. Then

a)		both spheres will have the same charge
b)		charges on 15cm spheres will be greater than that on 10 cm sphere
c)		charge on 10 cm sphere will be greater than that on 15cm spheres
d)		none of the above

25. Two capacitors with capacitance $C_{1}$ and $C_{2}$ are charged to a potentials $V_{1}$ and $V_{2}$ respectively. When they are combined in parallel, the ratio of their respective charges is

a)		$C_{1} / C_{2}$
b)		$V_{1} / V_{2}$
c)		$C_{1} C_{2} / (C_{1} + C_{2)}$
d)		${C^{2}}_{1} / {C^{2}}_{2}$

26. A sphere of radius 1 cm has a potential of $8000 V$ then energy density near its surface will be

a)		$64 \times 10^{5} J / m^{3}$
b)		$8 \times 10^{3} J / m^{3}$
c)		$32 J / m^{3}$
d)		$2.83 J / m^{3}$

27. The force between two charges 0.06m apart is 5N. If each charge is moved towards the other by 0.01m, the force between them is

a)		7.2N
b)		11.25N
c)		22.5N
d)		45N

28. A sphere carrying a charge Q coulomb and having a weight 'W' newton falls under gravity between vertical plates, 'd' meters apart. When potential difference of 'V' volts is applied between the plates the path makes an angle of $45^{0}$ with the vertical. The value of Q is

a)		W/2V
b)		W/V
c)		V/Wd
d)		Wd/V

29. A pellet carrying a charge of 0.5 C is accelerated through a P.D of 2000 volts. Its kinetic energy is

a)		1000ergs
b)		1000Joules
c)		1000KWh
d)		500Joules

30. The ratio of electric force between two protons to that between two electrons under similar conditions is of the order of

a)		$10^{38}$
b)		$1$
c)		zero
d)		$10^{42}$

31. One newton per coulomb is equivalent to

a)		$1 C / V$
b)		1J
c)		1 $V / m$
d)		1 $J / m$

32. The potential gradient at which the dielectric of a condenser just get punctured is called

a)		Dielectric constant
b)		Dielectric strength
c)		Dielectric resistance
d)		Dielectric number

33. Minimum number of capacitors of 2 $μ$ F each required to obtain a capacitor of 5 $μ$ F will be

a)		3
b)		4
c)		5
d)		6

34. Electric flux in an electric field 'E' through area 'ds' is given by

a)		$ɛ_{0}$ E.ds
b)		E.ds/ $ɛ_{0}$
c)		E.ds
d)		E X ds

35. The electric field due to a positive charge at a distance of 2m is 4N/C. Its magnitude at a distance of 4m will be

a)		2N/m
b)		0.5N/C
c)		1.5N/C
d)		N/C

36. A capacitor of capacitance 10 $μ$ F was originally charged to 10V. Now the P.D is increased to 20V. The increase in potential energy is

a)		$4 \times 10^{- 4} J$
b)		$10 \times 10^{- 4} J$
c)		$15 \times 10^{- 4} J$
d)		$5 \times 10^{- 4} J$

37. A parallel plate capacitor is with oil between the plates (dielectric constant=2) has a capacitance 'C'. If the oil is removed, the capacitance will be

a)		$\sqrt{2 C}$
b)		2C
c)		C/ $\sqrt{2}$
d)		C/2

38. The capacitance of the earth viewed as a spherical conductor of radius 6408 k is

a)		$980 μ$ F
b)		1424 $μ$ F
c)		712 $μ$ F
d)		$μ$ F

39. A parallel plate capacitor is charged. If the plates are pulled apart

a)		the P.D increases
b)		the capacitance increases
c)		the total charge increases
d)		the charge and P.D remains the same

40. The electric potential at a space is given by V=(5x+4y-7z). The electric field at the space is

a)		-(5i+4j-7k)
b)		5i+4j-7k
c)		-5i+4j
d)		-4j+7k

41. Two charges $Q_{1}$ and $Q_{2}$ repel each other if

a)		$Q_{1} > Q_{2}$
b)		$Q_{1} < Q_{2}$
c)		$Q_{1} Q_{2} = 0$
d)		$Q_{1} Q_{2} > 0$

42. Three charges q, Q and 4q are placed at one end, middle and other end of rod. The value of Q in order that the force on 'q' is zero must be

a)		4q
b)		-2q
c)		-q
d)		q/2

43. Air can sustain without breakdown of its insulation, an electric field of $3 \times 10^{6} V / m .$ The maximum amount of electrostatic energy density of air is

a)		$90 J / m^{3}$
b)		$79.6 J / m^{3}$
c)		$900 J / m^{3}$
d)		$39.8 J / m^{3}$

44. The electrics potential 'V' as a function of distance is given by $V = (5 x^{2} + 10 x - 9)$ volts. The value of electric field at x=1m is

a)		20V/m
b)		6V/m
c)		11V/m
d)		-23V/m

45. When two charged conductors at the same potential are joined by a wire, the energy of the conductor is

a)		increases
b)		decreases
c)		None of these
d)		No change

46. An uncharged condenser with a solid dielectric is connected to a similar air condenser charged to a P.D of $V_{1}$ volts. What is the dielectric constant of the solid dielectric

a)		$(V_{1} + V) / V$
b)		${V_{1}}^{2} / V$
c)		$(V_{1} - V) / V$
d)		$({V_{1}}^{2} - V^{2}) / ({V_{1}}^{2} + V^{2})$

47. A charge of 5C experiences a force of 2N in an electric field. The potential gradient at that point is

a)		0.4N/C
b)		$4 \times 10^{5} N / C$
c)		$2.5 \times 10^{- 6} N / C$
d)		Zero

48. The electric potential at the surface of an atomic nucleus (Z=50) of radius $9 \times 10^{- 15} m$

a)		80V
b)		$8 \times 10^{6} V$
c)		$9 V$
d)		$9 \times 10^{6} V$

49. The number of electrons to be put on a spherical conductor of radius 0.1 m to produce an electric field of 0.36N/C just above the surface is

a)		$2.7 \times 10^{6}$
b)		$2.6 \times 10^{6}$
c)		$2.5 \times 10^{6}$
d)		$2.4 \times 10^{6}$

50. When an electric dipole is placed in a uniform electric field, it experiences

a)		force only
b)		torque only
c)		Both force and torque
d)		Neither force nor torque