#### 12th Standard Physics English Medium Electromagnetic Waves Reduced Syllabus Important Questions With Answer Key 2021

12th Standard

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Physics

Time : 01:00:00 Hrs
Total Marks : 105
Multiple Choice Question
15 x 1 = 15
1. If the magnetic monopole exists, then which of the Maxwell’s equation to be modified?.

(a)

$\oint { \vec { E } .d\vec { A } } =\frac { { Q }_{ enclosed } }{ { \in }_{ 0 } }$

(b)

$\oint { \vec { E } .d\vec { A } }$=0

(c)

$\oint { \vec { E } .d\vec { A } } ={ \mu }_{ 0 }{ I }_{ enclosed }+{ \mu }_{ 0 }{ \in }_{ 0 }\frac { d }{ dt } \oint { \vec { E } .d\vec { A } }$

(d)

$\oint { \vec { E } .d\vec { l } } =-\frac { d }{ dt } { \Phi }_{ B }$

2. Who produced the electromagnetic waves first?

(a)

J.C.Bose

(b)

Marconi

(c)

Maxwell

(d)

Hertz

3. The existence of E.M. waves was confirmed experimentally by

(a)

Hertz

(b)

Maxwell

(c)

Huygens

(d)

Planck

4. Electromagnetic waves are discovered by

(a)

Hertz

(b)

Maxwell

(c)

Lenz

(d)

Huygens

5. Cellular phones use radio frequencies in

(a)

AM band

(b)

UHF band

(c)

FM band

(d)

upto 54 MHz

6. Which of the following can be used to take photograph over long distance of

(a)

White light

(b)

(c)

(d)

Microwaves

7. Which one of the following groups of electromagnetic waves is in order of increasing frequency?

(a)

Microwaves U-V rays, X-rays

(b)

Radio waves, visible light and 1-R rays

(c)

gamma rays U-V rays radio waves

(d)

gamma rays, U-V rays radio waves

8. In Hertz experiment, the formula for the frequency is _____

(a)

$\frac { 1 }{ 2\pi \sqrt { \frac { L }{ C } } }$

(b)

$\frac { \sqrt { LC } }{ 2\pi }$

(c)

$\frac { 1 }{ 2\pi \sqrt { LC } }$

(d)

$\frac { 2\pi }{ \sqrt { LC } }$

9. In E.M. waves, the variations in electric and magnetic fields are at an angle of________.

(a)

(b)

60°

(c)

90°

(d)

270°

10. The electromagnetic waves are __________ by electric and magnetic fields

(a)

deflected

(b)

not deflected

(c)

oscillated

(d)

scanned

11. The frequency of electromagnetic radiation Hertz produced was _________ Hz.

(a)

108

(b)

5x107

(c)

3x108

(d)

6x105

12. Microwaves ovens are the domestic application of ________ wave.

(a)

UV

(b)

visible

(c)

(d)

micro

13. ________ radiations are used to study atomic structure.

(a)

UV

(b)

IR

(c)

X-rays

(d)

Gamma

14. We can make long distance photographs using _________.

(a)

(b)

visible light

(c)

X-rays

(d)

IR rays

15. The dark lines in the solar spectrum are called _______ lines.

(a)

Fresnel

(b)

Newton

(c)

Compton

(d)

Fraunhofer

16. 2 Marks
10 x 2 = 20
17. What is displacement current?

18. Write down the integral form of modified Ampere’s circuital law.

19. Explain the concept of intensity of electromagnetic waves.

20. What is meant by Fraunhofer lines?

21. Write the uses of Micro waves.

22. (i) In which situation is there a displacement current but no conduction current?
(ii) Find the displacement current across the plate of the capacitor whose charging current is 0.25 A.

23. Arrange the Electromagnetic waves in order of
(i) increasing frequency
(ii) decreasing wavelength.

24. Which part of the Electromagnetic spetrum spectrum is used in operating a RADAR and why?

25. Which part of Electromagnetic is absorbed from sunlight by ozone layer?
(i) Write its source and
(ii) mention its uses.

26. What is the orgin of displacement currtent?

27. 3 Marks
10 x 3 = 30
28. Consider a parallel plate capacitor which is maintained at potential of 200 V. If the separation distance between the plates of the capacitor and area of the plates are 1 mm and 20 cm2. Calculate the displacement current for the time in μs.

29. Write down Maxwell equations in integral form.

30. Write short notes on
(a) microwave
(b) X-ray
(d) visible spectrum

31. Discuss briefly the experiment conducted by Hertz to produce and detect electromagnetic spectrum.

32. Explain the Maxwell’s modification of Ampere’s circuital law.

33. What is emission spectra?. Give their types.

34. How does Ampere - Maxwell law expalain the flux of current trough a capacitor when it is being charged by a battery? write the expression for the displacement current in terms of the rate of change of electric flux.

35. Write the generalised expression for the Ampere's circuital law in terms of Ic & Id. Mention the situation when there is
(i) only conduction current &no displacement current (Id).
(ii) only Id&no Ic.

36. Identify the Electromagnetic waves whose wavelength vary as
(a) 10-12 m to 10-8 m
(b) 10-4m and write their uses.

37. Name the parts of Electromagnetic spectrum which is
(i) used to destroy becteria.
(ii) produced by where is a sudden deceleration of high speed electrons.
(iii) used in food industry.

38. 5 marks
8 x 5 = 40
39. Consider a parallel plate capacitor whose plates are closely spaced. Let R be the radius of the plates and the current in the wire connected to the plates is 5 A, calculate the displacement current through the surface passing between the plates by directly calculating the rate of change of flux of electric field through the surface.

40. A transmitter consists of LC circuit with an inductance of 1 μH and a capacitance of 1 μF. What is the wavelength of the electromagnetic waves it emits?

41. Show how to generalize Ampere's circuital law to include the term due to displacement current?

42. In an Electromagnetic wave propagating along X - direction, the magnetic field osciallates at a frequency. 5 x 108 Hz and has an amplitude of 10-7 tesla, acting along the Y-direction.
(i) What is the wavelength of the wave?
(ii) Write the expression representing the corresponding oscillating electric field.

43. In a plane Electromagnetic wave the electric field oscillates sinusoidally at a frequency of 1.5 X 1010Hz & amplitude 36 Vm-1.
(i) What is the wavelength of a wave?
(ii) What the amplitude of the oscillating magnetic field?
(iii) Straight the average energy density of the electric field $\left( \overrightarrow { E } \right)$ , is equal to average energy density of the magnetic field $\left( \overrightarrow { B } \right)$

44. The magnetic field amplitude of an Electromagnetic wave is 1.6 x 10-7 T. If the frequency is 30 MHz. determine electric field, any velocity K and λ.

45. In an electric circuit, there is a capacitor of reactance 100 Ω connected across the source of 220 V, find the displacement current.

46. A plane Electromagnetic wave travels in vacuum along z - direction. What can you say about the directions of electric and magnetic field vectors? If the frequency of the wave is 30 MHz. What is its wavelength?