#### 12th Standard Physics English Medium Free Online Test one mark questions with answer key 2020 - Part Ten

12th Standard

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Physics

Time : 00:25:00 Hrs
Total Marks : 25
25 x 1 = 25
1. If voltage applied on a capacitor is increased from V to 2V, choose the correct conclusion

(a)

Q remains the same, C is doubled

(b)

Q is doubled, C doubled

(c)

C remains same, Q doubled

(d)

Both Q and C remain same

2. 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

3. Which of the following cannot be the units of electric field intensity?

(a)

NC-1

(b)

Vm-1

(c)

JC-1/m

(d)

JC-1

4. A wire of resistance 2 ohms per meter is bent to form a circle of radius 1m. Th e equivalent resistance between its two diametrically opposite points, A and B as shown in the fi gure is

(a)

$\pi \Omega$

(b)

$\frac{\pi}{2}\Omega$

(c)

2$\pi \Omega$​​​​​​​

(d)

$\frac{\pi}{4}\Omega$

5. Temperature co-effieient of resistance for metals is

(a)

constant

(b)

positive

(c)

zero

(d)

negative

6. When a current of 5 A flows through a conductor of resistance 3 $\Omega$ the loss of power due to joule heating effect is_________

(a)

75 W

(b)

25 W

(c)

70.7 W

(d)

45 W

7. An electron moves straight inside a charged parallel plate capacitor of uniform charge density σ. Th e time taken by the electron to cross the parallel plate capacitor when the plates of the capacitor are kept under constant magnetic fi eld of induction $\vec { B }$is

(a)

${ \varepsilon }_{ ° }\frac { eIB }{ \sigma }$

(b)

${ \varepsilon }_{ ° }\frac { IB }{ \sigma {I} }$

(c)

${ \varepsilon }_{ ° }\frac { IB }{ {e}\sigma }$

(d)

${ \varepsilon }_{ ° }\frac { IB }{ \sigma }$

8. What is the current passing through a coil of radius of 8 cm having 50 turns, when a magnetic intensity at the centre of the coil is 125 A turns m-1?

(a)

0.1 ampere

(b)

0.4 ampere

(c)

1 ampere

(d)

4 ampere

9. 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

10. Unit of inductive reactance is ___________

(a)

ohm-metre

(b)

mho-metre-1

(c)

ohm

(d)

mho

11. Which of the following E.M waves has the longest wavelength?

(a)

(b)

IR

(c)

X-rays

(d)

visible

12. The radius of curvature of curved surface at a thin planoconvex lens is 10 cm and the refractive index is 1.5. If the plane surface is silvered, then the focal length will be,

(a)

5cm

(b)

10 cm

(c)

15 cm

(d)

20 cm

13. If an object moves towards a plane mirror with a speed V at an angle θ to the perpendicular to the plane of the mirror,find the relative velocity between the object and the image,

(a)

V

(b)

2V

(c)

2 V cosθ

(d)

2 V sin θ

14. 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

15. The mean wavelength of light from sun is taken to be 550 nm and its mean power is 3.8 × 1026W. The number of photons received by the human eye per second on the average from sunlight is of the order of

(a)

1045

(b)

1042

(c)

1054

(d)

1051

16. Photoelectric cells are used to control _______ of furnaces.

(a)

pressure

(b)

temperature

(c)

output power

(d)

input

17. An a-particle of energy 10 meV is scattered through 1800 by a fixed uranium nucleus. The distance of the closest approach is of the order of

(a)

(b)

10-10 cm

(c)

10-12 cm

(d)

10-15 cm

18. The charge of an alpha-particle is _______________

(a)

same as that of a proton

(b)

twice as that of an electron

(c)

thrice as that of an proton

(d)

twice as that of a neutron

19. A good _____ slows down neutrons by elastic collisions and it does not remove them by absorption.

(a)

fuel

(b)

moderator

(c)

coolant

(d)

control rod

20. Which of the following is not the advantage of PN junction diode over tube value?

(a)

Unlimited life

(b)

No warming-up time after switching

(c)

Large efficiency

(d)

Low consumption of power

21. The expression of Y in the following circuit is

(a)

AB + CD

(b)

A + BCD

(c)

A+B+C+D

(d)

A. B. C. D

22. If the distance between the conduction band and valence band is leV, then this combination is

(a)

semiconductor

(b)

metal

(c)

insulator

(d)

conductor

23. Large band width for higher data is achieved by using

(a)

Large band width for higher data is achieved
by using

(b)

high frequency audio wave

(c)

low frequency carrier wave

(d)

low frequency audio wave

(a)

It is less noisy

(b)

reproduction is of much better quality

(c)

it is more noisy

(d)

both (a) & (b)

25. Optical fiber communication is generally prefered over general communication system because

(a)

it has signal security

(b)

it is more efficient

(c)

it cannot be jammed as easily as radio waves

(d)

all of the above