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#### Quarterly Model Question Paper

12th Standard EM

Reg.No. :
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Physics

Time : 02:45:00 Hrs
Total Marks : 70
15 x 1 = 15
1. Two identical point charges of magnitude –q are fi xed as shown in the fi gure below. A third charge +q is placed midway between the two charges at the point P. Suppose this charge +q is displaced a small distance from the point P in the directions indicated by the arrows, in which direction(s) will +q be stable with respect to the displacement

(a)

A1 and A2

(b)

B1 and B2

(c)

both directions

(d)

No stable

2. An electric field $\vec { E } =10x\hat { i }$ exists in a certain region of space. Then the potential difference V = Vo – VA, where Vo is the potential at the origin and VA is the potential at x = 2 m is:

(a)

10 J

(b)

-20 J

(c)

+20 J

(d)

-10 J

3. An uncharged metal sphere is placed between two equal and oppositely charged metal plates. The nature of lines of force will be

(a)

(b)

(c)

(d)

4. The magnitude of electric dipole moment of water molecule is

(a)

6 x 10-30 cm

(b)

6.2 x 10-30 cm

(c)

6.1 x 10-30

(d)

5.95 10-30 cm

5. Which of the following statement on equipotential surface is wrong?

(a)

The potential difference between any two points on the surface, is zero.

(b)

The electric field is always perpendicular to the surface

(c)

Equipotential surface is always spherical.

(d)

No work is done in moving a charge along the surface

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. Relative permittivity (εr) is also known as ________

(a)

dielectric strength

(b)

dielectric constant

(c)

polarisability

(d)

susceptibility

8. Electric field intensity and electric potential are related by_________.

(a)

E=-$\frac{dV}{dt}$

(b)

E=-$\frac{dV}{dx}$

(c)

E=$\frac{dV}{dt}$

(d)

E=$\frac{-dx}{dV}$

9. Two wires of A and B with circular cross section made up of the same material with equal lengths. Suppose RA = 3 RB, then what is the ratio of radius of wire A to that of B?

(a)

3

(b)

$\sqrt3$

(c)

$\frac{1}{\sqrt3}$

(d)

$\frac{1}{3}$

10. Temperature co-effieient of resistance for metals is

(a)

constant

(b)

positive

(c)

zero

(d)

negative

11. Two identical resistors are connected in parallel then connected in series. The effective resistance are in the ratio

(a)

1:2

(b)

2:1

(c)

1:4

(d)

4:1

12. Thermo electric generators are used in power plants to convert_________ into electricity ..

(a)

light energy

(b)

waste heat

(c)

sound energy

(d)

hydro energy

13. A thin insulated wire forms a plane spiral of N = 100 tight turns carrying a current I = 8 m A (milli ampere). The radii of inside and outside turns are a = 50 mm and b = 100 mm respectively.
The magnetic induction at the center of the spiral is

(a)

$5\mu T$

(b)

$7\mu T$

(c)

$8\mu T$

(d)

$10\mu T$

14. When the current changes from +2A to −2A in 0.05 s, an emf of 8 V is induced in a coil. Th e co-efficient of self-induction of the coil is

(a)

0.2H

(b)

0.4H

(c)

0.8H

(d)

0.1H

15. Which one of them is used to produce a propagating electromagnetic wave?.

(a)

an accelerating charge

(b)

a charge moving at constant velocity

(c)

a stationary charge

(d)

an uncharged particle

16. 6 x 2 = 12
17. What is the general definition of electric dipole moment?

18. What is dielectric breakdown.

19. What is electric power and electric energy?

20. State Joule’s law of heating.

21. Mention the ways of producing induced emf.

22. What is meant by Fraunhofer lines?

23. 6 x 3 = 18
24. Derive the expressions for the potential energy of a system of point charges.

25. What are carbon resistors? What does the colour indicates?

26. Tabulate the difference between Coulomb's law and Biot-Savort's law.

27. The magnetic flux passes perpendicular to the plane of the circuit and is directed into the paper. If the magnetic flux varies with respect to time as per the following relation: $\Phi_B$=(2t3+3t2+8t+5)mWb, what is the magnitude of the induced emf in the loop when t = 3 s? Find out the direction of current through the circuit.

28. Explain the working of a single-phase AC generator with necessary diagram.

29. How does the capacitive reactance depend on frequency? & What is the reactance of a capacitor at hertz to the study at?

30. 5 x 5 = 25
31. Four charges are arranged at the corners of the square PQRS of side a as shown in the figure.(a) Find the work required to assemble these charges in the given configuration. (b) Suppose a charge q′ is brought to the center of the square, by keeping the four charges fixed at the corners, how much extra work is required for this?

32. Three points A, B & C lie in a uniform electric field (E) of 5 x 103 NC-1 Find the potential difference between A &c.

33. Calculate the potential at a point P due to charge of 5 x 10-7Clocated 11cm away.

34. In a metre bridge the balancing length is found to be 40 cm from end A. If a resistance of 10 $\Omega$ is connected in series with R, balanceing length is obtained 60 em from A. calculate the valueR&S.

35. A toroidal solenoid with air core has an average radius of 15cm, area of cross section 12cm2 and has 2000 turns. Calculate the self- inductance of the toroid. Assume the field to be uniform across the cross-section of the toroid.