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

12th Standard

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Physics

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Time : 00:25:00 Hrs
Total Marks : 25

Answer all the questions

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. In electrostatics if the charges are in motion, another force named __________ comes into play in addition to coulomb force

(a)

Lorentz force

(b)

Repulsive force

(c)

Attractive force

(d)

electromagnetic force

3. Van de Graaff generator produces an electrostatic potential difference of_______ volts.

(a)

108

(b)

109

(c)

107

(d)

1010

4. When a point charge of 6mC is moved between two points in an electric field, the work done is 1.8 x 10-5 J. The potential difference between the two points is

(a)

1.08 V

(b)

1.08 μV

(c)

2 V

(d)

30 V

5. Near a charged object A another earthed object B is placed. Charges are induced on B. If B is removed. After that the charge on A ________.

(a)

remains the same

(b)

decreases

(c)

increases

(d)

becomes zero

6. 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

7. A square aluminum rod is 1 m long and 5 mm on edge. What must be the radius of another aluminum rod whose length is 1 m and which has the same resistance as that of square Aluminum rod?

(a)

1.4 mm

(b)

2.8 mm

(c)

4.2 mm

(d)

5.6 mm

8. Copper Wire metals and burns out when the current increases above______

(a)

5 A

(b)

10 A

(c)

25 A

(d)

25 A

9. Two identical coils, each with N turns and radius R are placed coaxially at a distance R as shown in the fi gure. If I is the current passing through the loops in the same direction, then the magnetic field at a point P which is at exactly at$\frac { R }{ 2 }$ distance between two coils is

(a)

$\frac { 8N{ \mu }_{ ° }I }{ \sqrt { 5 } R }$

(b)

$\frac { 8N{ \mu }_{ ° }I }{ { 5 }^{ \frac { 3 }{ 2 } }R }$

(c)

$\frac { 8N{ \mu }_{ ° }I }{ { 5 }R }$

(d)

$\frac { 4N{ \mu }_{ ° }I }{ \sqrt { 5 } R }$

10. Direction of magnetic force on a positive charge moving in a magnetic field is given by

(a)

thumb rule

(b)

left hand rule

(c)

right hand rule

(d)

cork screw rule

11. The heat developed in half a minute in a resistor of resistance 5Ω is 15,000 joules. The current through the resistor is

(a)

5 ampere

(b)

100 ampere

(c)

40 ampere

(d)

10 ampere

12. The magnetic declination for chennai is _______

(a)

-1° 5'

(b)

1°8'

(c)

-1°8'

(d)

1°5'

13. 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

14. In an a. c. dynamo, the induced current is _________ in nature.

(a)

alternating

(b)

increasing

(c)

decreasing

(d)

constant

15. Gamma rays are used in the treatment of __________

(a)

cancer

(b)

AIDS

(c)

Polio

(d)

TB

16. An object is placed in front of a convex mirror of focal length of f and the maximum and minimum distance of an object from the mirror such that the image formed is real and magnified.

(a)

2f and c

(b)

c and $\infty$

(c)

f and O

(d)

None of these

17. The wavelength λe of an electron and λp of a photon of same energy E are related by

(a)

λp $\alpha$ λe

(b)

${ \lambda }_{ p }\alpha \sqrt { { \lambda }_{ e } }$

(c)

${ \lambda }_{ p }\alpha \frac { 1 }{ \sqrt { { \lambda }_{ e } } }$

(d)

${ \lambda }_{ p }\alpha { \lambda }_{ e }^{ 2 }$

18. Sodium and copper have work functions of 2.3eV and 4.5eV respectively, then the ratio of the wavelengths is nearest to

(a)

1: 2

(b)

4: 1

(c)

2: 1

(d)

1: 4

19. Electrons when accelerated in a cyclotron acquires ________

(a)

zero mass

(b)

higher mass

(c)

zero velocity

(d)

uniform acceleration

20. Suppose an alpha particle accelerated by a potential of V volt is allowed to collide with a nucleus whose atomic number is Z, then the distance of closest approach of alpha particle to the nucleus is

(a)

$14.4\frac { Z }{ V } \mathring { A }$

(b)

$14.4\frac { V }{ Z } \mathring { A }$

(c)

$1.44\frac { Z }{ V } \mathring { A }$

(d)

$1.44\frac { V }{ Z } \mathring { A }$

21. The explosion of hydrogen bomb is based on the principle of

(a)

uncontrolled fission reaction

(b)

nuclear fusion reaction

(c)

controlled fission

(d)

photo electric effect

22. Th e principle in which a solar cell operates

(a)

Diffusion

(b)

Recombination

(c)

Photovoltaic action

(d)

Carrier flow

23. In a video signal for transmission of picture what value of bandwidth is used in communication system?

(a)

2.4 MHz

(b)

4:2 MHz

(c)

24MHz

(d)

42 MHz

24. The transmitter in a RADAR is a high power ________.

(a)

cyclotron oscillator

(b)

magnetron oscillator

(c)

Hartley oscillator

(d)

simple harmonic oscillator

25. In actual practice, the range of uplink frequencies used is _________ GHz.

(a)

5.725 - 7.075

(b)

3.4 - 4.8

(c)

6 - 10

(d)

9 - 10