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

12th Standard

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Physics

Time : 00:25:00 Hrs
Total Marks : 25
25 x 1 = 25
1. Four Gaussian surfaces are given below with charges inside each Gaussian surface. Rank the electric fl ux through each Gaussian surface in increasing order.

(a)

D < C < B < A

(b)

A < B = C < D

(c)

C < A = B < D

(d)

D > C > B > A

2. In a parallel plate capacitor of capacitance C, a metal sheet is inserted between the plates, parallel to them. The thickness of the sheet is half of the separation between the plates. The capacitance now becomes

(a)

2C

(b)

$\frac{C}{4}$

(c)

4C

(d)

$\frac{C}{2}$

3. In a hollow spherical shell potential (V) changes with respect to distance (r) from centre.
$\left[ { V }_{ inside }=\frac { Q }{ 4\pi { \varepsilon }_{ 0 }R } r\le R,\quad { V }_{ outside }=\frac { Q }{ 4\pi { \varepsilon }_{ 0 }r } r\ge R,V\alpha \frac { 1 }{ r } \right]$

(a)

(b)

(c)

(d)

4. Two wires of A and B with circular cross section made up of the same material with equal lengths. Suppose RA = 3 RB, then what is the ratio of radius of wire A to that of B?

(a)

3

(b)

$\sqrt3$

(c)

$\frac{1}{\sqrt3}$

(d)

$\frac{1}{3}$

5. When the free electrons are moving in all possible directions, the value of the current produced is_______

(a)

lA

(b)

2A

(c)

0 A

(d)

1.2A

6. The BH curve for a ferromagnetic material is shown in the figure. The material is placed inside a long solenoid which contains 1000 turns/cm. The current that should be passed in the solenonid to demagnetize the ferromagnet completely is

(a)

1.00 m A (milli ampere)

(b)

1.25 mA

(c)

1.50 mA

(d)

1.75 mA

7. A galvanometer can be converted into a voltmeter by connecting

(a)

a low resistance in parallel to it

(b)

a high resistance in parallel to it

(c)

a low resistance in series with it

(d)

a high resistance in series with it

8. The magnitude of the induced emf in a conductor depends on the

(a)

flux density of the magnetic field

(b)

amount of flux cut

(c)

(d)

rate of change of flux

9. During the propagation of electromagnetic waves in a medium

(a)

electric energy density is double of the magnetic energy density

(b)

electric energy density is half of the magnetic energy density

(c)

electric energy density is equal to the magnetic energy density

(d)

both electric and magnetic energy densities are zero

10. Electromagnetic waves are __________.

(a)

longitudinal waves

(b)

mechanical waves

(c)

Transverse waves

(d)

Straight waves

11. The relation between velocity of light, permeability and permittivity of free space in________.

(a)

${ C }^{ 2 }=\frac { 1 }{ { \mu }_{ 0 }{ \varepsilon }_{ 0 } }$

(b)

$C=\frac { 1 }{ { \mu }_{ 0 }{ \varepsilon }_{ 0 } }$

(c)

${ \mu }_{ 0 }={ \varepsilon }_{ 0 }c$

(d)

${ \varepsilon }_{ 0 }={ \mu }_{ 0 }c$

12. _________ spectra are used for making dyes

(a)

continuous emission

(b)

band emission

(c)

band absorption

(d)

line spectra

13. In a Young’s double-slit experiment, the slit separation is doubled. To maintain the same fringe spacing on the screen, the screen-to-slit distance D must be changed to,

(a)

2D

(b)

$\frac{D}{2}$

(c)

$\sqrt{2}$D

(d)

$\frac{D}{\sqrt2}$

14. In photoelectric emission, a radiation whose frequency is 4 times threshold frequency of a certain metal is incident on the metal. Th en the maximum possible velocity of the emitted electron will be

(a)

$\sqrt { \frac { { hv }_{ 0 } }{ m } }$

(b)

$\sqrt { \frac { { 6hv }_{ 0 } }{ m } }$

(c)

$2\sqrt { \frac { { hv }_{ 0 } }{ m } }$

(d)

$\sqrt { \frac { { hv }_{ 0 } }{2m } }$

15. According to Einstein's photo electric equation. the graph between the K.E of photo electrons ejected and the frequency of incident radiation is

(a)

(b)

(c)

(d)

16. The energy of the electron in the first orbit of hydrogen atom is -13.6 eV. Its potential energy is

(a)

-13.6 eV

(b)

13.6eV

(c)

-27.2 eV

(d)

27.2 eV

17. Th e principle in which a solar cell operates

(a)

Diffusion

(b)

Recombination

(c)

Photovoltaic action

(d)

Carrier flow

18. A current gain for, a transistor working as CB amplifier is 0.90. If emitter current is 10 mA, then base current is

(a)

1mA

(b)

2 mA

(c)

0.1 mA

(d)

0.2 mA

19. A p-n diode can be used as

(a)

condenser

(b)

amplifier

(c)

rectifier

(d)

regulator

20. In modulation process) radio frequency wave is termed as

(a)

modulated wave

(b)

modulating wave

(c)

carrier wave

(d)

none

21. After the angle of refraction becomes 90o at the ionosphere, the wave travels _________.

(a)

faster

(b)

through space

(c)

in a straight line

(d)

towards the earth

22. The total variation in frequency of a FM transmitter is called _______

(a)

signal swing

(b)

carrier swing

(c)

shift

(d)

difference

23. 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

24. The blue print for making ultra durable synthetic material is mimicked from

(a)

Lotus leaf

(b)

Morpho butterfly

(c)

Parrot fish

(d)

Peacock feather

25. George Devol invented the first digitally operated programmable robot called

(a)

Unimate

(b)

Robotics

(c)

Motors

(d)

Generators