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#### Model 1 Mark Book Back Questions (New Syllabus) 2020

12th Standard EM

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Physics

Time : 00:30:00 Hrs
Total Marks : 31

Part A

31 x 1 = 31
1. The figure shows tow parallel equipotential surface A and B kept at a small distance 'r' a part from each other. A point change of Q coulomb is taken from the surface A to B. The amount of net work done will be

(a)

$W=\frac { -1 }{ 4\pi { \varepsilon }_{ 0 }r } \frac { q }{ r }$

(b)

$W=\frac { 1 }{ 4\pi { \varepsilon }_{ 0 }r } \frac { q }{ r }$

(c)

$W=\frac { -1 }{ 4\pi { \varepsilon }_{ 0 }r } \frac { q }{ r^2 }$

(d)

zero

2. Two condensers (capacitors) of capacity C1 and C2 are connected in parallel. A charge Q given to then is shared. The ratio of the charges Q is

(a)

$\frac { { C }_{ 2 } }{ { C }_{ 1 } }$

(b)

$\frac { { C }_{ 1 } }{ { C }_{ 2 } }$

(c)

C1.C2

(d)

$\frac { 1 }{ { C }_{ 1 }\times { C }_{ 2 } }$

3. The expression for the electric field due to a surface of total charge 'Q' is given by

(a)

$\overset { \rightarrow }{ E } =\frac { 1 }{ 4\pi { \varepsilon }_{ 0 } } \int { \frac { \sigma dA }{ { r }^{ 2 } } } \hat { r }$

(b)

$\overset { \rightarrow }{ E } =\frac { 1 }{ 4\pi { \varepsilon }_{ 0 } } \int { \frac { \rho dA }{ { r }^{ 2 } } } \hat { r }$

(c)

$\overset { \rightarrow }{ E } =\frac { 1 }{ 4\pi { \varepsilon }_{ 0 } } \int { \frac { \lambda dl }{ { r }^{ 2 } } } \hat { r }$

(d)

$\overset { \rightarrow }{ E } =\frac { 1 }{ 4\pi { \varepsilon }_{ 0 } } \int { \frac { dq }{ { r }^{ 2 } } } \hat { r }$

4. The unit for electric flux is

(a)

C2N-1m-2

(b)

Nm2C-2

(c)

Nm2C-1

(d)

Nm-2C-1

5. The temperature co-efficient of resistance for alloys is

(a)

low

(b)

very low

(c)

high

(d)

very high

6. If the specific resistance of a potentiometer wire is 10-7 Om and current flowing through it . is 0.1 amp, cross - sectional area of wire is 10-6 m2, then potential gradient will be

(a)

10-2 v/m

(b)

10-4 v/m

(c)

10-6 v/m

(d)

10-8v/m

7. Electrical resistance is given by

(a)

$R=\cfrac { Al }{ \sigma }$

(b)

$R=\cfrac { l }{ \sigma A }$

(c)

$R=\cfrac { \sigma A }{ l }$

(d)

$R=\cfrac { \sigma }{ Al }$

8. Graph of force per unit length between long parallel current carrying conductors, and the distance between them is

(a)

straight line

(b)

parabola

(c)

ellipse

(d)

rectangular hyperbola

9. In Joule's law, when the current passed through the circuit is doubled keeping resistance (R) and time of passage of current (t) constant, temperature

(a)

increases twice

(b)

increases four times

(c)

increases sixteen times

(d)

decreases four times

10. The force on a proton moving with a speed of 105 m/s perpendicular to a magnetic field 10-3 tesla is ______

(a)

1.6 x 10-17 N

(b)

1.6 x 10-27 N

(c)

1.6 x 10-19 N

(d)

10-2 N

11. If a secondary coil has 40 turns, and a primary coil with 20 turns is charged with 50V of potential difference, then potential difference in secondary would be

(a)

50 V

(b)

25 V

(c)

60 V

(d)

100 V

12. Speed of electromagnetic wave is the same for all

(a)

wavelength

(b)

media

(c)

intensities

(d)

frequencies

13. Cellular phones use radio-waves in ______ band

(a)

long wave

(b)

ultra high frequency

(c)

short frequency

(d)

medium frequency

14. Two plane mirror are at right angles to each other. A man stands between them and combs hair with his right hand. In how many of the images will he be seen using his right hand.

(a)

None

(b)

1

(c)

2

(d)

3

15. Photoelectron effect supports quantum nature of light because

(a)

there is a minimum frequency which no photo electrons are emitted

(b)

the maximum kinetic energy of photo electrons depends only one the frequency of light and not in intensity

(c)

even when the metal surface is faintly illuminated the photoelectrons leave the surface immedietly

(d)

All the above

16. Einstein's photoelectric equation is

(a)

W+hv=$\frac{1}{2}$m V2max

(b)

$\frac{1}{2}$mV2max = W

(c)

hv+$\frac{1}{2}$mV2max = W

(d)

W+$\frac{1}{2}$mV2max = W

17. The wavelength associated with electrons on acceleration is generally of the order of metres.

(a)

5 x 10-12

(b)

6 x 10-10

(c)

7 x 10-9

(d)

60

18. When hydrogen atom is in its first excited level, its radius is __________ of the Bohr radius.

(a)

twice

(b)

same

(c)

half

(d)

four times

19. For first order X-ray diffraction, the wavelength in of the X-ray is equal to the lattice spacing at a glancing angle is

(a)

15°

(b)

60°

(c)

45°

(d)

30°

20. The velocity of cathode rays is upto ________ the velocity of light.

(a)

0.10

(b)

0.001

(c)

10.5

(d)

0.01

21. Radio isotope _________ is used in the treatment of cancer.

(a)

sodium

(b)

cobalt

(c)

iron

(d)

phosphorous

22. The forward based diode is

(a)

(b)

(c)

(d)

23. The forbidden energy band gap in semi conductor, conductor and insulator are E1, E2 and E3 respectively. The relation among them is

(a)

E1. < E2 > E3

(b)

E1 > E2 > E3

(c)

E1 < E2 < E3

(d)

E1 > E2 < E3

24. A light emitting diode has a voltage drop of 2v across it when 10 mA current is passed. If this LED is to be operated with 6v battery the value of limiting resistor would be ___________

(a)

400 Ω

(b)

4000 Ω

(c)

40 k Ω

(d)

300 Ω

25. Current gain in common emitter configuration is more than 1because

(a)

IC < IE

(b)

IC < IB

(c)

IE > IB

(d)

IC> IE

26. When the output is an complement of the input it is ____________

(a)

NOT gate

(b)

AND gate

(c)

OR

(d)

NAND

27. Audio signal cannot be transmitted because

(a)

the signal has more noise

(b)

the signal cannot be amplitude for distance communication

(c)

the transmitting antenna length is very small to design

(d)

the transmitting antenna length is very large and impracticable

28. In an AM receiver, the local oscillator frequency is 2750 kHz. The tuned in station frequency is

(a)

2905 kHz

(b)

2295 kHz

(c)

3055 kHz

(d)

2250 kHz

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

(a)

cyclotron oscillator

(b)

magnetron oscillator

(c)

Hartley oscillator

(d)

simple harmonic oscillator

30. _______ is synthesized top down approach

(a)

Ball milling

(b)

Plasma etching

(c)

lithography

(d)

Ball milling and lithography

31. In __________ it was established that atoms are made up of electrons, protons and neutrons

(a)

1945

(b)

1923

(c)

1930

(d)

1927