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Electromagnetic Waves MCQs for NEET — Physics Questions with Answers

Practice free Electromagnetic Waves (Physics) NEET multiple-choice questions online with instant answers and detailed explanations. No login required.

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A parallel plate capacitor consists of two circular plates each of radius 12 cm and separated by 5.0 mm. The capacitor is being charged by an external source. The charging current is constant and is equal to 0.15 A. The rate of change of the potential difference between the plates will be :

$1.873 \times 10^{7} V / s$

$1.873 \times 10^{8} V / s$

$1.873 \times 10^{9} V / s$

$1.873 \times 10^{10} V / s$

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Explanation

$C = \frac{ε_{0} A}{d} = 8.85 \times 10^{- 12} \times \frac{π \times {(0.12)}^{2}}{5 \times 10^{- 3}} = 0.08 \times 10^{- 9} F \frac{d V}{d t} = \frac{1}{C} \frac{d q}{d t} = \frac{i}{C} = \frac{0.15}{0.08 \times 10^{- 9}} = 1.873 \times 10^{9} V / s e c$

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A lamp emits monochromatic green light uniformly in all directions. The lamp is 3% efficient in converting electrical power to electromagnetic waves and consumes 100 W of power. The amplitude of the electric field associated with the electromagnetic radiation at a distance of 5 m from the lamp will be

1.34 V/m

2.68 V/m

4.02 V/m

5.36 V/m

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Explanation

Power of Em waves = 3% of 100 W = 3 W

Intensity= $\frac{P}{A} = \frac{3}{4 π {(5)}^{2}} = 0.0096 \frac{W}{m^{2}}$

$T h e n, I = \frac{1}{2} \in_{0} C E_{0}^{2} \Rightarrow E_{0} = \sqrt{\frac{2 I}{\in_{0} C}} = 2.68 v / m$

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A parallel plate capacitor consists of two circular plates each of radius 2 cm, separated by a distance of 0.1 mm. If the voltage across the plates is varying at the rate of $5 \times 10^{13}$ V/s, then the value of displacement current is :

5.50 A

$5.56 \times 10^{2} A$

5.56 $\times 10^{3}$ A

$2.28 \times 10^{4} A$

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Explanation

$I_{D} = C \frac{dV}{dt} = \frac{ε_{0} A}{d} \frac{dV}{dt} I_{D} = \frac{8.85 \times 10^{- 12} \times 3.14 \times {(2 \times 10^{- 2})}^{2}}{0.1 \times 10^{- 3}} \times 5 \times 10^{13} = 5.56 \times 10^{3} A$

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In an electromagnetic wave, the direction of the magnetic field induction $\vec{B}$ is

parallel to electric field $\vec{E}$

perpendicular to electric field $\vec{E}$

antiparallel to Poynting vector $\vec{S}$

random

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Explanation

Magnetic field and electric field are mutually perpendicular to each other as well as to the direction of wave

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In an electromagnetic wave

Power is transmitted along the magnetic field

Power is transmitted along the electric field

Power is equally transferred along with the electric and magnetic fields

power is transmitted in a direction perpendicular to both the fields

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Explanation

power is transmitted in a direction perpendicular to both the fields.

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For any E.M. wave if E = 100 V/m and B = 3.33 $\times 10^{- 7}$ . Then the rate of energy flow per unit area is

$3.33 \times 10^{- 5} J / m^{2}$

26.5 W/ $m^{2}$

$3 \times 10^{8} J / m^{2}$

None of these

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Explanation

$S_{0} = E_{0} \times H_{0} = 100 \times 0.265 = 26.5 W / m^{2}$

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A variable frequency AC source is connected to a capacitor. Then on increasing the frequency

Both conduction current and displacement current will increase

Both conduction current and displacement current will decrease

Conduction current will increase and displacement will decrease

Conduction current will decrease and displacement current will increase

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Explanation

Both conduction current and displacement current will increase.

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Source of an electromagnetic wave is

A charge moving with constant velocity

A charge at rest

A charge moving in a circular orbit

Charges cannot produce an EM wave

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Explanation

Electromagnetic waves are produced by accelerated charged.

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The dimension of E/H is that of

Impedance

Inductance

capacitance

Inductance $\times$ Capacitance

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Explanation

$D i m e n s i o n o f \frac{E}{H} = \frac{V / m}{A / m} = \frac{V}{A} = u n i t o f i m p e d e n c e$

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Poynting vector $\vec{P}$ for an EM wave is :

$\vec{P} = \vec{E} \times \vec{B}$

$\vec{P} = \vec{E} \times \vec{H}$

$\vec{P} = \frac{\vec{E}}{\vec{B}}$

$\vec{P} = \frac{\vec{E}}{\vec{H}}$

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Explanation

Poynting vector $\vec{P}$ is given by $\vec{P} = \vec{E} \times \vec{H}$ .

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