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#### 12th Standard Physics English Medium Free Online Test 1 mark questions 2020 - Part Six

12th Standard EM

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Physics

Time : 00:25:00 Hrs
Total Marks : 25
25 x 1 = 25
1. 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

2. Based on Franklin's convention amber rods are_________.

(a)

positively charged

(b)

negatively charged

(c)

neutral

(d)

none of the above

3. The direction of electric field at a point the equatorial line due to an electric dipole is

(a)

along the equatorial line towards the dipole.

(b)

along the equatorial line away from the dipole

(c)

parallel to the axis of the dipole and opposite to the direction of dipole moment

(d)

parallel to the axis of the dipole and in the direction of dipole moment.

4. A carbon resistor of (47 ± 4.7 ) k Ω to be marked with rings of diff erent colours for its identifi cation. Th e colour code sequence will be

(a)

Yellow – Green – Violet – Gold

(b)

Yellow – Violet – Orange – Silver

(c)

Violet – Yellow – Orange – Silver

(d)

Green – Orange – Violet - Gold

5. A piece of copper and another of germanium are cooled from room temperature to 80 K. The resistance of

(a)

each of them increases

(b)

each of them decreases

(c)

copper increases and germanium decreases

(d)

copper decreases and germanium increases

6. A bird sitting on an insulated wire carrying a current feels quite safe because

(a)

the bird is a non-conductor of electricity

(b)

resistance of the bird is very large

(c)

there is a large potential difference between bird and wire

(d)

there is no potential difference between bird and wire

7. The unit of temperature coefficient of resistance is_______.

(a)

°C

(b)

°C-1

(c)

-C-2

(d)

°C2

8. For a given thermocouple for a given cold junction temperature, the inversion is 220°C. When the cold junction temperature is increased by 20°C, then the inversion temperature is

(a)

200°C

(b)

220°C

(c)

240°C

(d)

110°C

9. A current of 2A flows through a circular coil of area 4π x 10-2 m2. The magnetic field at the centre of the coil is

(a)

62.8 x 10-6T

(b)

628 x 10-6T

(c)

6.28 x 10-6T

(d)

3.14 x 10-6T

10. In an electrical circuit, R, L, C and AC voltage source are all connected in series. When L is removed from the circuit, the phase difference between the voltage and current in the circuit is $\frac{\pi}{3}$. Instead, if C is removed from the circuit, the phase difference is again  $\frac{\pi}{3}$.  The power factor of the circuit is

(a)

1/2

(b)

1/$\sqrt2$

(c)

1

(d)

$\sqrt3$/2

11. In Fleming's right hand rule, the forefinger represents the direction of

(a)

motion of the conductor

(b)

magnetic field

(c)

induced current

(d)

induced emf

12. AC generator works on the principle of

(a)

self induction

(b)

mutual induction

(c)

electromagnetic induction

(d)

none of these

13. 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

14. The phase difference between electric and magnetic field vectors in the electromagnetic waves?

(a)

$\frac{\pi}{4}$

(b)

$\frac{\pi}{2}$

(c)

$\pi$

(d)

zero

15. One of the of Young’s double slits is covered with a glass plate as shown in figure. The position of central maximum will,

(a)

get shifted downwards

(b)

get shifted upwards

(c)

will remain the same

(d)

data insufficient to conclude

16. A man of length h requires a mirror of length at least equal to, to see his own complete image

(a)

$\cfrac { h }{ 4 }$

(b)

$\cfrac { h }{ 2 }$

(c)

$\cfrac { h }{ 2 }$

(d)

h

17. A boy stands straight infront of a mirror at a distance of 30 cm away from it. He sees his erect image whose height is  $\cfrac { 1 }{ 5 }$ of his real height. The mirror he is using is

(a)

plane mirror

(b)

convex mirror

(c)

concave lens

(d)

plano - convex mirror

18. When a metallic surface is illuminated with radiation of wavelength λ, the stopping potential is V. If the same surface is illuminated with radiation of wavelength 2λ, the stopping potential is $\frac{V}{4}$. The threshold wavelength for the metallic surface is

(a)

(b)

(c)

$\frac{5}{2}λ$

(d)

19. ______ theory explains photo electric effect.

(a)

Electromagnetic

(b)

Quantum

(c)

Wave

(d)

Corpuscular

20. ______ lenses are used in electron microscope.

(a)

Optical

(b)

Glass

(c)

Silica

(d)

Electromagnetic

21. In a hydrogen atom, the electron revolving in the fourth orbit, has angular momentum equal to

(a)

h

(b)

$\frac{h}{\pi}$

(c)

$\frac{4h}{\pi}$

(d)

$\frac{2h}{\pi}$

22. Arrange the spectral lines Hα, Hβ, Hγ, Hδ in the increasing order of their wavelength

(a)

Hα, Hβ, H, Hδ

(b)

Hδ, H, Hβ, Hα

(c)

Hβ, Hα Hδ, H

(d)

Hα, Hβ, Hγ, Hδ

23. The barrier potential of a silicon diode is approximately

(a)

0.7 V

(b)

0.3V

(c)

2.0 V

(d)

2.2V

24. ____________ electrons occupy the conduction band.

(a)

Ground state

(b)

Free

(c)

Bound

(d)

Valence

25. The particle size of ZnO material is 30 nm. Based on the dimension it is classified as

(a)

Bulk material

(b)

Nanomaterial

(c)

Soft material

(d)

Magnetic material