JEE Main 2021 (Online) 16th March Morning Shift | Electromagnetic Waves Question 84 | Physics

1

JEE Main 2021 (Online) 16th March Morning Shift

MCQ (Single Correct Answer)

+4

-1

For an electromagnetic wave travelling in free space, the relation between average energy densities due to electric (U_e) and magnetic (U_m) fields is :

A

U_e = U_m

B

U_e $$\ne$$ U_m

C

U_e < U_m

D

U_e > U_m

2

JEE Main 2021 (Online) 24th February Evening Shift

MCQ (Single Correct Answer)

+4

-1

Match List - I with List - II.

	List I		List II
(a)	Source of microwave frequency	(i)	Radioactive decay of nucleus
(b)	Source of infrared frequency	(ii)	Magnetron
(c)	Source of Gamma Rays	(iii)	Inner shell electrons
(d)	Source of X-rays	(iv)	Vibration of atoms and molecules
		(v)	LASER
		(vi)	RC circuit

Choose the correct answer from the options given below :

A

(a)-(vi), (b)-(v), (c)-(i), (d)-(iv)

B

(a)-(ii), (b)-(iv), (c)-(i), (d)-(iii)

C

(a)-(ii), (b)-(iv), (c)-(vi), (d)-(iii)

D

(a)-(vi), (b)-(iv), (c)-(i), (d)-(v)

3

JEE Main 2020 (Online) 6th September Evening Slot

MCQ (Single Correct Answer)

+4

-1

For a plane electromagnetic wave, the magnetic field at a point x and time t is

$$\overrightarrow B \left( {x,t} \right)$$ = $$\left[ {1.2 \times {{10}^{ - 7}}\sin \left( {0.5 \times {{10}^3}x + 1.5 \times {{10}^{11}}t} \right)\widehat k} \right]$$ T

The instantaneous electric field $$\overrightarrow E $$ corresponding to $$\overrightarrow B $$ is :
(speed of light c = 3 × 10⁸ ms^–1)

A

$$\overrightarrow E \left( {x,t} \right) = \left[ {36\sin \left( {1 \times {{10}^3}x + 1.5 \times {{10}^{11}}t} \right)\widehat i} \right]$$ $${V \over m}$$

B

$$\overrightarrow E \left( {x,t} \right) = \left[ {36\sin \left( {0.5 \times {{10}^3}x + 1.5 \times {{10}^{11}}t} \right)\widehat k} \right]{V \over m}$$

C

$$\overrightarrow E \left( {x,t} \right) = \left[ {36\sin \left( {1 \times {{10}^3}x + 0.5 \times {{10}^{11}}t} \right)\widehat j} \right]{V \over m}$$

D

$$\overrightarrow E \left( {x,t} \right) = \left[ { - 36\sin \left( {0.5 \times {{10}^3}x + 1.5 \times {{10}^{11}}t} \right)\widehat j} \right]{V \over m}$$

4

JEE Main 2020 (Online) 5th September Evening Slot

MCQ (Single Correct Answer)

+4

-1

The correct match between the entries in column I and column II are :

I	II
Radiation	Wavelength
(a) Microwave	(i) 100 m
(b) Gamma rays	(ii) 10^–15 m
(c) A.M. radio waves	(iii) 10^–10 m
(d) X-rays	(iv) 10^–3 m

A

(a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)

B

(a)-(iv), (b)-(ii), (c)-(i), (d)-(iii)

C

(a)-(iii), (b)-(ii), (c)-(i), (d)-(iv)

D

(a)-(i), (b)-(iii), (c)-(iv), (d)-(ii)