Electromagnetic Waves Chapter-Wise Test 4

Correct answer Carries: 4.

Wrong Answer Carries: -1.

An electromagnetic wave in vacuum has a magnetic field amplitude of \( B_0 = 4 \times 10^{-8} \, \text{T} \). What is the electric field amplitude? (Given \( c = 3 \times 10^8 \, \text{m/s} \))

Using \( E_0 = B_0 c \), we have \( E_0 = (4 \times 10^{-8}) \times (3 \times 10^8) = 12 \, \text{V/m} \).

6 V/m
8 V/m
10 V/m
12 V/m
4

Which of the following cannot produce electromagnetic waves?

Electromagnetic waves are produced by accelerated charges. Stationary charges produce only electrostatic fields, not time-varying fields required for EM waves.

An oscillating charge
A charge moving with uniform velocity
A charge undergoing acceleration
A charge in circular motion
2

Why do microwaves heat food more effectively than infrared waves in domestic microwave ovens?

Microwaves are tuned to the resonant frequency of water molecules, causing them to oscillate and generate heat via friction, whereas infrared waves primarily heat surfaces through absorption.

Higher frequency of microwaves
Resonance with water molecules
Greater penetration of infrared
Lower energy of microwaves
2

What fundamental asymmetry exists between electric and magnetic fields in Maxwell’s equations?

Maxwell’s equations show an asymmetry because electric charges (sources of electric fields) exist, but magnetic monopoles (hypothetical sources of magnetic fields) do not, as indicated by Gauss’s law for magnetism.

No magnetic monopoles exist
Electric fields are always stronger
Magnetic fields cannot change
Electric fields require a medium
1

What physical principle explains why electromagnetic waves can exhibit interference and diffraction?

Electromagnetic waves exhibit wave-like behavior due to their sinusoidal nature, allowing superposition, which leads to phenomena like interference and diffraction.

Static field interactions
Particle nature
Wave-like behavior
Medium dependence
3

What is the typical wavelength range of microwaves used in domestic microwave ovens?

The document mentions that microwaves range from \( 0.1 \, \text{m} \) to \( 1 \, \text{mm} \), and domestic microwave ovens typically use wavelengths around a few centimeters within this range.

\( > 0.1 \, \text{m} \)
\( 0.1 \, \text{m} \) to \( 1 \, \text{mm} \)
\( 400 \, \text{nm} \) to \( 0.6 \, \text{nm} \)
\( 10^{-10} \, \text{m} \) to \( 10^{-14} \, \text{m} \)
2

Why are infrared waves sometimes referred to as heat waves?

The document explains that infrared waves are absorbed by water molecules, increasing their thermal motion and thus heating the material.

They have the highest frequency
They are emitted by cold bodies
They increase thermal motion in materials
They are not absorbed by any material
3

Why are microwaves used in satellite communication?

Microwaves can penetrate the atmosphere with minimal absorption and are easily directed into narrow beams, making them ideal for satellite communication over long distances.

High absorption
Penetration and directionality
Low frequency
Visible spectrum
2

An electromagnetic wave in vacuum has a wavelength of \( 6 \, \text{m} \). What is its frequency? (Given \( c = 3 \times 10^8 \, \text{m/s} \))

Using \( v \lambda = c \), we have \( v = \frac{c}{\lambda} = \frac{3 \times 10^8}{6} = 5 \times 10^7 \, \text{Hz} \).

\( 3 \times 10^7 \, \text{Hz} \)
\( 4 \times 10^7 \, \text{Hz} \)
\( 5 \times 10^7 \, \text{Hz} \)
\( 6 \times 10^7 \, \text{Hz} \)
3

What physical implication arises from the fact that electromagnetic waves are transverse in nature?

Being transverse means that the oscillations of electric and magnetic fields are perpendicular to the direction of propagation, allowing polarization phenomena to occur in electromagnetic waves.

They can be polarized
They require a medium
They travel slower in vacuum
They cannot carry energy
1

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