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#### 12th Standard Physics English Medium Free Online Test One Mark Questions with Answer Key 2020 - Part Four

12th Standard EM

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Physics

Time : 00:25:00 Hrs
Total Marks : 25
25 x 1 = 25
1. A thin conducting spherical shell of radius R has a charge Q which is uniformly distributed on its surface. The correct plot for electrostatic potential due to this spherical shell is

(a)

(b)

(c)

(d)

2. The given figure is a plot of lines of force due to two charges q1 & q2 find out the sign of charges

(a)

both negative

(b)

both positive

(c)

upper positive and lower negative

(d)

upper negative and lower positive

3. A wire connected to a power supply of 230 V has power dissipation P1. Suppose the wire is cut into two equal pieces and connected parallel to the same power supply. In this case power dissipation is P2. The ratio $\frac{P_2}{P_1}$ is

(a)

1

(b)

2

(c)

3

(d)

4

4. In the case of Wheatstone)s Bridge) the bridge balance condition will be obtained only when____

(a)

the current through the galvanometer is maximum

(b)

the current through the galvanometer is minimum

(c)

the current through the galvanometer is zero

(d)

the current through the galvanometer is infinity

5. Two short bar magnets have magnetic moments 1.20 Am2 and 1.00 Am2 respectively. They are kept on a horizontal table parallel to each other with their north poles pointing towards the south. They have a common magnetic equator and are separated by a distance of 20.0 cm. The value of the resultant horizontal magnetic induction at the mid-point O of the line joining their centers is (Horizontal components of Earth’s magnetic induction is 3.6 x 10-5 Wb m-2 )

(a)

3.60 × 10-5 Wb m-2

(b)

3.5 × 10-5 Wb m-2

(c)

2.56 × 10-4 Wb m-2

(d)

2.2 × 10-4 Wb m-2

6. When the current flowing in a circular coil is doubled and the number of turns of the coil in it is halved, the magnetic field at its centre will become

(a)

four times

(b)

same

(c)

half

(d)

double

7. The direction of force on a current carrying conductor placed in a magnetic field is given by _____

(a)

Fleming's Left Hand Rule

(b)

Fleming's Right Hand Rule

(c)

Ampere's velocity

(d)

Biot-Savart Law

8. In a series RL circuit, the resistance and inductive reactance are the same. Then the phase difference between the voltage and current in the circuit is

(a)

$\frac{\pi}{4}$

(b)

$\frac{\pi}{2}$

(c)

$\frac{\pi}{6}$

(d)

zero

9. An emf of 12V is induced when the current in the coil changes at the rate of 40 A S-1. The coefficient of self induction of the coil is

(a)

0.3 H

(b)

0.003 H

(c)

30 H

(d)

4.8 H

10. The reactance of a capacitor is,

(a)

Xc = Cω

(b)

Xc$\frac{1}{Cω}$

(c)

Xc$\frac{C}{ω}$

(d)

Xc$\frac{ω}{C}$

11. Which one of them is used to produce a propagating electromagnetic wave?.

(a)

an accelerating charge

(b)

a charge moving at constant velocity

(c)

a stationary charge

(d)

an uncharged particle

12. Which of the following is a special aspect of EM wave?

(a)

can be deflected by electric field

(b)

can be deflected by magnetic filed

(c)

can be deflected by both electric & magnetic filed

(d)

none of these

13. The wavelength range of microwave is _______m

(a)

10-8 to 0.35

(b)

10-3 to 0.3

(c)

10-8 to 10-6

(d)

10-3 to 10-1

14. A point source of light B is placed at a distance L in front of the centre of a mirror of width d hung vertically on a wall. A man walks is front of the mirror along a line parallel to the mirror at a distance 2 L front it as shown. The greatest distance over  which he can see the image of the light source in the mirror is

(a)

d/2

(b)

d

(c)

2d

(d)

3d

15. A diminished virtual image can be formed only in

(a)

Plane mirror parabolic mirror

(b)

A concave mirror

(c)

A convex mirror

(d)

concave

16. A concave mirror is used to focus the image of a flower on a nearby well 120 cm from the flower. If a lateral magnification of 16 is desired, the distance of the flower from the mirror should be

(a)

8 cm

(b)

12 cm

(c)

80 cm

(d)

120 cm

17. 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

18. A charged oil drop is suspended in uniform field of 3 x I04 Vm-1 so that it neither falls nor rises. The charge on the drop will be

(a)

3.3 x 10-18C

(b)

3.2 x 10-18 C

(c)

1.6 x 10-18C

(d)

4.8 x 10-18C

19. The anode of a simple photo emissive cell is _______

(a)

glass tube

(b)

quartz crystal

(c)

platinum wire

(d)

iron rod

20. The clocks in moving ships will appear to go _______ clocks on earth.

(a)

faster than

(b)

slower than

(c)

the same as

(d)

stops after leaving earth

21. According to to Bohr, the relation between principal quantum number (n) and radius of the orbit (r) is

(a)

r α $\frac1n$

(b)

r α $\frac{1}{n^2}$

(c)

r α n

(d)

r α n2

22. A N-P-N transistor' conducts when collector is _________ and emitter is ________ with respect to base

(a)

positive, negative

(b)

positive, positive

(c)

negative, negative

(d)

negative, positive

23. The maximum carrier swing allowed in frequency modulation is :

(a)

455 kHz

(b)

10.7 kHz

(c)

75 MHz

(d)

150 kHz

24. The alloys used for muscle wires in Robots are

(a)

Shape memory alloys

(b)

Gold copper alloys

(c)

Gold silver alloys

(d)

Two dimensional alloys

25. The size of the Nano robots is reduced to ________ level to perform a task in very small space.

(a)

Macroscopic

(b)

Robots DNA

(c)

Microscopic

(d)

Bacteria