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

12th Standard

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Physics

Time : 01:00:00 Hrs
Total Marks : 105
Multiple Choice Questions
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. The phase and orientation of the magnetic vector associated with electromagnetic oscillations differ respectively from those of the corresponding electric vectors by

(a)

zero, zero

(b)

$\frac{\pi}{2}$,$\frac{\pi}{2}$

(c)

0, $\frac{\pi}{2}$

(d)

0,$\frac{\pi}{2}$

3. Which one of the following is not an electromagnetic waves?

(a)

Gamma rays

(b)

X-rays

(c)

Beta rays

(d)

Microwaves

4. Calcium or Barium salts in bunsen flame, CO2, N2 molecule, NH3 gas in a discharge tube gives_______.

(a)

line emission spectra

(b)

continuous emission spectra

(c)

line absorption spectra

(d)

band spectra

5. __________discovered electromagnetic induction.

(a)

(b)

Maxwell

(c)

Ampere

(d)

Hertz

6. In an electromagnetic wave, the electric and magnetic fields are at an angle ___________ to the direction of propagation.

(a)

270°

(b)

90°

(c)

180°

(d)

67°

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

(a)

deflected

(b)

not deflected

(c)

oscillated

(d)

scanned

8. ________ absorption spectrum are used to study molecular structure.

(a)

UV rays

(b)

IR

(c)

X-rays

(d)

૪-rays

9. _________ are used in forensic labs.

(a)

X-ray

(b)

UV

(c)

Gamma

(d)

Visible

10. Forged documents are detected through ________.

(a)

X-rays

(b)

UV-rays

(c)

IR-rays

(d)

microwaves

11. _________ emission spectrum is used to identify the gas used.

(a)

Continuous

(b)

Line

(c)

Band

(d)

Solid

12. Continuous spectrum depends only on the _________ of the source.

(a)

characteristic

(b)

temperature

(c)

density

(d)

volume

13. The absorption spectra are characteristic of the __________.

(a)

source

(b)

absorbing substance

(c)

time of travel from source to screen

(d)

spectrometer used to study the spectrum

14. If white light is passed through iodine vapour, ________ are obtained.

(a)

continuous absorption spectra

(b)

continuous emission spectra

(c)

band absorption spectra

(d)

emission spectra

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. What are electromagnetic waves?

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

20. What is meant by Fraunhofer lines?

21. Write the uses of Micro waves.

22. (i) How is the speed of Electromagnetic waves in vacuum determined by the electric and magnetic fields? and
(ii) Do Electromagnetic waves carry energy and momentum?

23. Why are Infra~ed radiation referred as heat waves? Name the radiations, which are next to these radiation having
(i) shorter λ
(ii) longer λ.

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

25. Draw a diagram depicting oscillating electric and magnetic field of an electromagnetic wave.

26. What is the orgin of displacement currtent?

27. 3 Marks

10 x 3 = 30
28. Write down Maxwell equations in integral form.

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

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

31. Write the uses of Infrared radiation

32. Write the production of gamma rays and mention its properties and uses.

33. The charge on a parallel plate capacitor varies as q=qo cos 2$\pi \gamma$t. The plates are very large and close together. (area-A. separation - d) find the displacement current through the capacitor?

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

36. 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.

37. Identify the following Electromagnetic radiations (a) 109 Hz (b) 1011 Hz. Give one application of each.

38. 5 Marks

8 x 5 = 40
39. Compute the speed of the electromagnetic wave in a medium if the amplitude of electric and magnetic fields are 3 × 104 NC-1 and 2 × 10-4 T, respectively.

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. If the relative permeability and relative permittivity of the medium is 1.0 and 2.25, respectively. Find the speed of the electromagnetic wave in this medium.

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

43. 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.

44. 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 $\left( \overrightarrow { B } \right)$

45. 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.

46. About 5 % of the power of a 100 W light bulb is connected to visible radiation. What is the average intensity of visible radiation at the distance of 1m from the bulb?