#### 12th Standard Physics English Medium Reduced Syllabus Important Questions - 2021 Part - 1

12th Standard

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Physics

Time : 01:00:00 Hrs
Total Marks : 160
Multiple Choice Questions
10 x 1 = 10
1. Which charge configuration produces a uniform electric field?

(a)

point Charge

(b)

infinite uniform line charge

(c)

uniformly charged infinite plane

(d)

uniformly charged spherical shell

2. An electric dipole is placed at an alignment angle of 300 with an electric fi eld of 2 × 105 NC-1. It experiences a torque equal to 8 N m. Th e charge on the dipole if the dipole length is 1 cm is

(a)

4 mC

(b)

8 mC

(c)

5 mC

(d)

7 mC

3. The total electric fl ux for the following closed surface which is kept inside water

(a)

$\frac { 80q }{ { \varepsilon }_{ 0 } }$

(b)

$\frac { q }{ { 40\varepsilon }_{ 0 } }$

(c)

$\frac { q }{ { 80\varepsilon }_{ 0 } }$

(d)

$\frac { q }{ { 160\varepsilon }_{ 0 } }$

4. The electric field created by a _________ is basically a non-uniform electric field.

(a)

Test charge

(b)

Positive charge

(c)

Negative charge

(d)

Point charge

5. The unit for electric susceptibility is

(a)

Nm2 C-2

(b)

C2 N-1 m-2

(c)

C-2Nm2

(d)

N-1 m-2C2

6. 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

7. In a large building, there are 15 bulbs of 40W, 5 bulbs of 100W, 5 fans of 80W and 1 heater of 1kW are connected. The voltage of electric mains is 220V. The minimum capacity of the main fuse of the building will be

(a)

14 A

(b)

8 A

(c)

10 A

(d)

12 A

8. In an oscillating LC circuit, the maximum charge on the capacitor is Q. The charge on the capacitor when the energy is stored equally between the electric and magnetic fields is

(a)

$\frac{Q}{2}$

(b)

$\frac{Q}{\sqrt3}$

(c)

$\frac{Q}{\sqrt2}$

(d)

Q

9. The electric and magnetic fields of an electromagnetic wave are

(a)

in phase and perpendicular to each other

(b)

out of phase and not perpendicular to each other

(c)

in phase and not perpendicular to each other

(d)

out of phase and perpendicular to each other

10. The threshold wavelength for a metal surface whose photoelectric work function is 3.313 eV is

(a)

4125 $\mathring { A }$

(b)

3750$\mathring { A }$

(c)

6000$\mathring { A }$

(d)

2062.5$\mathring { A }$

11. 2 Marks
15 x 2 = 30
12. What is meant by quantisation of charges?

13. Write a short note on superposition principle.

14. What is mean by ‘Electric field lines’?

15. What is the general definition of electric dipole moment?

16. Write a short note on ‘electrostatic shielding’.

17. What is a Capacitor?

18. What do you mean by Potential Energy of an electric dipole, when placed in electric field?

19. Gauss law is true for any closed surface, no matter what its shape or size is. Justify.

20. Two charge d spherical conditioners of radii R1 & R2 when connected by a conducting wire acquire charges q1 & q2 respectively. Find the ratio of surface charge densities in terms of their radii.

21. What is the effective resistance of resistors connected in series

22. What do you mean by parallel combination of cells.

23. Of which material is a potential wire normally made and why

24. State Coulomb’s inverse law.

25. What is forbidden energy gap?

26. What is called reverse saturation current?

27. 3 Marks
15 x 3 = 45
28. How do we determine the electric field due to a continuous charge distribution? Explain.

29. Derive an expression for electrostatic potential energy of the dipole in a uniform electric field.

30. Explain in detail the effect of a dielectric placed in a parallel plate capacitor.

31. What happens when and electric dipole is held in a non-uniform electric field?

32. What is dielectrics or insulators.

33. Define and derive an expression for the energy density in parallel plate capacitor.

34. How the emf of two cells are compared using potentiometer?

35. Derive an expression of drift velocity and write the relation between drift velocity and mobility.

36. Show that Lenz’s law is in accordance with the law of conservation of energy.

37. Define self-inductance of a coil interms of
(i) magnetic flux and
(ii) induced emf.

38. Write an expression for the momentum of Electromagnetic wave.

39. A variable frequency ac source is connected to capacitor. How will the displacement current change with decrease in frequency.

40. An electron and a proton have the same kinetic energy. Which one of the two has the larger de Broglie wavelength and why?

41. Derive the energy expression for hydrogen atom using Bohr atom model.

42. Write the applications of internet.

43. 5 Marks
15 x 5 = 75
44. The following figure represents the electric potential as a function of x – coordinate. Plot the corresponding electric field as a function of x.

45. A water molecule has an electric dipole moment of 6.3 × 10-30 Cm. A sample contains 1022 water molecules, with all the dipole moments aligned parallel to the external electric field of magnitude 3 × 105 NC-1. How much work is required to rotate all the water molecules from θ = 00 to 900?

46. Suppose a charge +q on Earth’s surface and another +q charge is placed on the surface of the Moon. (a) Calculate the value of q required to balance the gravitational attraction between Earth and Moon (b) Suppose the distance between the Moon and Earth is halved, would the charge q change?
(Take mE = 5.9 × 1024 kg, mM = 7.9 × 1022 kg)

47. Explain in detail the Electrostatic Potential difference between the charges.

48. A thin metallic spherical shell of radius R carries a charge Q on its surface. A point charge $\frac{Q}{2}$ is placed at the centre C and another is placed at the centre C and another a distance x from the centre as shown in the figure
(i) Find the electric flux through the shell.

(ii) Find the force on the charges at C and A.

49. A copper slab of mass 2g contains 2 x 1022 atoms. The charge on the nucleus of each atom is 29e. What fraction of the electrons must be removed from the sphere to give it a charge of +2μC?

50. Two point charges having equal charges separated by 1m distance experiences a force of 8N. What will be the force experienced by them, if they are held in water at the same distance?

51. An electric dipole of length 4cm, when placed with its axis making an angle of 60° with a uniform electric field, experiences a torque of 4√3 Nm. Calculate the potential energy of the dipole, if it has charge ±8nC.

52. From the given circuit,

Find
i) Equivalent emf of the combination
ii) Equivalent internal resistance
iii) Total current
iv) Potential difference across external resistance
v) Potential difference across each cell

53. Explain what is (i) Thomson effect, (ii) Positive Thomson effect, (iii) Negative effect.

54. Deduce and expression for Magnetic dipole moment of revolving electron around the nucleus in a circular orbit.

55. Draw graphs showing the distribution of charge in a capacitor and current through an inductor during LC oscillations with respect to time. Assume that the charge in the capacitor is maximum initially.

56. Straight in LC oscillations, the sum of energies stored in capacitor & the inductors is constant in time.

57. A wheel with 10 metallic spokes each 0.5m long is rotated with a speed of 120 rev/min in a plane normal to the horizontal component of the earth's magnetic field HE at a place if H= 0.4 G at the place) what is the induced emf between the a x k and the rim of the wheel? Take) 1 gauss (G) = 10-4T.

58. Write a note on RADAR and its applications.