#### frequently asked multiple choice questions twelfth standard physics

12th Standard EM

Reg.No. :
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Physics

Write register number only on the question paper
Time : 00:10:00 Hrs
Total Marks : 20

Part - A

20 x 1 = 20
1. A charge Q is placed at the corner of a cube. The electric flux through all the six faces of the cube is

(a)

$\frac { Q }{ { 3\varepsilon }_{ 0 } }$

(b)

$\frac { Q }{ { 6\varepsilon }_{ 0 } }$

(c)

$\frac { Q }{ { 8\varepsilon }_{ 0 } }$

(d)

$\frac { Q }{ { \varepsilon }_{ 0 } }$

2. Which graph shows the variation of electric field E due to a hollow spherical conductor of radius R as a function of distance from the centre of the sphere?

(a)

(b)

(c)

(d)

3. In a hollow spherical shell potential (V) changes with respect to distance (r) from centre.
$\left[ { V }_{ inside }=\frac { Q }{ 4\pi { \varepsilon }_{ 0 }R } r\le R,\quad { V }_{ outside }=\frac { Q }{ 4\pi { \varepsilon }_{ 0 }r } r\ge R,V\alpha \frac { 1 }{ r } \right]$

(a)

(b)

(c)

(d)

4. What physical quantities may X and Y represent? [Y represents the first mentioned quantity].

(a)

K.E - velocity of a particle

(b)

pressure - temperature of a given gas (constant volume)

(c)

capacitance - charge to give a constant potential

(d)

potential - capacitance to give a constant charge

5. During charging a capacitor variation of potential V of the capacitor with time t as shown a

(a)

(b)

(c)

(d)

6. Charge Q on a capacitor varies with voltage Vas shown in graph, where Q is along X-axis and V along Y-axis. The area of triangle OAB represents

(a)

capacitance

(b)

capacitive reactance

(c)

magnetic field between the plates

(d)

energy stored in the capacitor

7. A condenser of 2μF capacitance is charged steadily from 0 to 5 coulomb. Which of the following graphs correctly represents the variation of potential difference across its plates with respect to the charge on the condensor [Q = C V ]

(a)

(b)

(c)

(d)

8. In two concentric hollow spheres of radii r and R (>r), the charge Q is distributed such that their surface densities are some. Then the potential at their common centre is

(a)

$\frac { Q({ R }^{ 2 }+{ r }^{ 2 }) }{ 4\pi { \varepsilon }_{ 0 }(R+r) }$

(b)

$\frac { QR }{ R+r }$

(c)

zero

(d)

$\frac { Q({ R }+{ r }) }{ 4\pi { \varepsilon }_{ 0 }({ R }^{ 2 }+{ r }^{ 2 }) }$

9. A point charge q is placed at a distance a/2 directly above the centre of a square of side 'a'.The electric flux through the square is

(a)

$\frac { q }{ { \varepsilon }_{ 0 } }$

(b)

$\frac { q }{ { \pi \varepsilon }_{ 0 } }$

(c)

$\frac { q }{ {4 \pi \varepsilon }_{ 0 } }$

(d)

$\frac { q }{ {6 \pi \varepsilon }_{ 0 } }$

10. A polythene piece rubbed with wool is found to have negative charge of 3.2 x 10-7C. Estimate the number of electrons transferred from wool to polythene

(a)

2x1012

(b)

3x1012

(c)

4x1012

(d)

5x1012

11. A Gaussian surface in the figure is shown by dotted line. The electric field on the surface will be

(a)

due to q1 and q2 only

(b)

due to q2 only

(c)

zero

(d)

due to all

12. A charge q is placed at the centre of a cubical box of side with top open. The flux of electric field through the surface of the cubical box is

(a)

Zero

(b)

$\frac { q }{ { \varepsilon }_{ 0 } }$

(c)

$\frac { q }{ 6{ \varepsilon }_{ 0 } }$

(d)

$\\ \frac { 5q }{ 6{ \varepsilon }_{ 0 } }$

13. Electric field intensity at a point due to an infinite sheet of charge having surface charge density σ is E. If the sheet were conducting, electric intensity would be

(a)

$\frac{E}{2}$

(b)

E

(c)

2E

(d)

4E

14. Surface density of charge on a sphere of radius R in terms of electric intensity E at a distance r in free space is

(a)

${ \varepsilon }_{ 0 }E{ \left( \frac { R }{ r } \right) }^{ 2 }$

(b)

$\frac { { \varepsilon }_{ 0 }ER }{ { r }^{ 2 } }$

(c)

${ \varepsilon }_{ 0 }E{ \left( \frac { r }{ R } \right) }^{ 2 }$

(d)

${ e }_{ 0 }E\frac { r }{ { R }^{ 2 } }$

15. The electric flux over a sphere of radius 1m is ф. If radius of the sphere were doubled without changing the charge enclosed, electric flux would become

(a)

(b)

$\\ \\ \\ \frac { \phi }{ 2 }$

(c)

$\\ \\ \\ \frac { \phi }{ 4 }$

(d)

ф

16. Electric field at a distance r from infinitely long conducting sheet is proportional to

(a)

r1

(b)

r2

(c)

r3/2

(d)

independent of r

17. A charge q is enclosed as shown in fig. The electric flux is

(a)

maximum in (i)

(b)

maximum in (ii)

(c)

maximum in (iii)

(d)

equal in all

18. A charge q1 exerts force on charge q2. If another charge q3 is brought near, the force of q1, exerted on q2, will be

(a)

decreased

(b)

increased

(c)

remains unchanged

(d)

increased if q3 is of same sign as q1 and decreased if q2 is of opposite sign.

19. Find the electric field at x =5m from the graph.

(a)

2 V/m

(b)

-2.5 V/m

(c)

2/5 V/m

(d)

-2/5 V/m

20. Van de Graaff generator produces an electrostatic potential difference of_______ volts.

(a)

108

(b)

109

(c)

107

(d)

1010