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#### Important 1 Mark Book Back Questions (New Syllabus) 2020

12th Standard EM

Reg.No. :
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Physics

Time : 00:20:00 Hrs
Total Marks : 20

Part A

24 x 1 = 24
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. Two identical conducting balls having positive charges q1 and q2 are separated by a center to center distance r. If they are made to touch each other and then separated to the same distance, the force between them will be

(a)

less than before

(b)

same as before

(c)

more than before

(d)

zero

3. A toaster operating at 240 V has a resistance of 120 Ω. Th e power is

(a)

400 W

(b)

2 W

(c)

480 W

(d)

240 W

4. What is the value of resistance of the following resistor?

(a)

100 k Ω

(b)

10 k Ω

(c)

1k Ω

(d)

1000 k Ω

5. 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

6. A circular coil of radius 5 cm and 50 turns carries a current of 3 ampere. The magnetic dipole moment of the coil is

(a)

1.0 amp – m2

(b)

1.2 amp – m2

(c)

0.5 amp – m2

(d)

0.8 amp – m2

7. Th ree wires of equal lengths are bent in the form of loops. One of the loops is circle, another is a semi-circle and the third one is a square. Th ey are placed in a uniform magnetic fi eld and same electric current is passed through them. Which of the following loop confi guration will experience greater torque ?

(a)

circle

(b)

semi-circle

(c)

square

(d)

all of them

8. A thin semi-circular conducting ring (PQR) of radius r is falling with its plane vertical in a horizontal magnetic fi eld B, as shown in the fi gure.

The potential diff erence developed across the ring when its speed v, is

(a)

Zero

(b)

$\frac { { Bv\pi { r }^{ 2 } } }{ 2 }$and P is at higher potential

(c)

πrBv and R is at higher potential

(d)

2rBvand R is at higher potential

9. A circular coil with a cross-sectional area of 4 cm2 has 10 turns. It is placed at the centre of a long solenoid that has 15 turns/cm and a cross-sectional area of 10 cm2. The axis of the coil coincides with the axis of the solenoid. What is their mutual inductance?

(a)

7.54 μH

(b)

8.54 μH

(c)

9.54 μH

(d)

10.54 μH

10. Which of the following are false for electromagnetic waves

(a)

transverse

(b)

mechanical waves

(c)

longitudinal

(d)

produced by accelerating charges

11. Let E = Eo sin[106 x -ωt] be the electric field of plane electromagnetic wave, the value of ω is

(a)

(b)

(c)

(d)

12. Which of the following is NOT true for electromagnetic waves?

(a)

it transport energy

(b)

it transport momentum

(c)

it transport angular momentum

(d)

in vacuum, it travels with different speeds which depend on their frequency

13. If the velocity and wavelength of light in air is Va and λa and that in water is Vw and λw, then the refractive index of water is,

(a)

$\frac{V_W}{V_a}$

(b)

$\frac{V_a}{V_W}$

(c)

$\frac{\lambda_W}{\lambda_a}$

(d)

$\frac{{V_a}\lambda_W}{{V_W}\lambda_a}$

14. A ray of light strikes a glass plate at an angle 60o. If the reflected and refracted rays are perpendicular to each other, the refractive index of the glass is,

(a)

$\sqrt3$

(b)

$\frac{3}{2}$

(c)

$\sqrt{\frac{3}{2}}$

(d)

2

15. A particle of mass 3 × 10–6 g has the same wavelength as an electron moving with a velocity 6 10 × 6m s−1. The velocity of the particle is

(a)

1.82x10-18ms-1

(b)

9x10-2ms-1

(c)

3x10-15ms-1

(d)

1.82x10-15ms-1

16. If a light of wavelength 330 nm is incident on a metal with work function 3.55 eV, the electrons are emitted. Then the wavelength of the emitted electron is (Take h = 6.6 × 10–34 Js)

(a)

<2.75×10−9m

(b)

≥2.75×10−9m

(c)

≤2.75×10−12m

(d)

<2.5×10−10m

17. The charge of cathode rays is

(a)

Positive

(b)

negative

(c)

neutral

(d)

not defined

18. If a half –wave rectifi ed voltage is fed to a load resistor, which part of a cycle the load current will flow?

(a)

00–900

(b)

900–1800

(c)

00–1800

(d)

00–3600

19. The internationally accepted frequency deviation for the purpose of FM broadcasts

(a)

75 kHz

(b)

68 kHz

(c)

80 kHz

(d)

70 kHz

20. Which of the following is an example of breadcast made of communication?

(a)

(b)

Television

(c)

Mobile

(d)

both (a) & (b)

21. For base station to mobile communication, the required frequency band is

(a)

540 - 1600 KHz

(b)

200 - 32 MHz

(c)

840 - 935 MHz

(d)

5.9 - 6.42 GHz

22. The made of propagation used by short wave broadcast services is

(a)

space wave

(b)

skywave

(c)

ground wave

(d)

both (a) & (c)

23. The materials used in Robotics are

(a)

Aluminium and silver

(b)

Silver and gold

(c)

Copper and gold

(d)

Steel and aluminum

24. Nanoscience is the science of object with typical sizes of ___________

(a)

1 - 100 μ

(b)

1 - 100 nm

(c)

1 - 100 cm

(d)

1- 100 m