Electromagnetic Waves Chapter-Wise Test 1

Correct answer Carries: 4.

Wrong Answer Carries: -1.

An electromagnetic wave in vacuum has a frequency of \( 60 \, \text{MHz} \). What is its wavelength? (Given \( c = 3 \times 10^8 \, \text{m/s} \))

Using \( v \lambda = c \), we have \( \lambda = \frac{c}{v} = \frac{3 \times 10^8}{60 \times 10^6} = 5 \, \text{m} \).

2.5 m
5 m
7.5 m
10 m
2

What is one environmental concern related to the depletion of the ozone layer mentioned in the document?

The document mentions that the depletion of the ozone layer by chlorofluorocarbons (CFCs) allows more UV radiation to reach Earth, posing health risks.

Increased infrared radiation
Reduced greenhouse effect
Excessive radio wave interference
Increased UV radiation exposure
4

In the electromagnetic spectrum, why are gamma rays associated with nuclear processes?

Gamma rays are produced by high-energy nuclear transitions or radioactive decay, as their extremely short wavelengths correspond to the energy scales of nuclear phenomena.

Low energy emission
Nuclear energy scales
Thermal emission
Visible spectrum
2

What explains the effectiveness of infrared waves in remote sensing applications?

Infrared waves interact with materials based on their temperature and composition, allowing remote sensing devices to detect variations in heat signatures or material properties.

High frequency
Visible spectrum
Low penetration
Thermal interaction
4

What is the relationship between the amplitudes of electric and magnetic fields in an electromagnetic wave in vacuum? (Given \( c = 3 \times 10^8 \, \text{m/s} \))

From Maxwell's equations, the amplitudes are related as \( B_0 = \frac{E_0}{c} \), where \( c \) is the speed of light in vacuum.

\( B_0 = \frac{E_0}{c} \)
\( E_0 = \frac{B_0}{c} \)
\( E_0 = B_0 c^2 \)
\( B_0 = E_0 c^2 \)
1

An electromagnetic wave in vacuum has an electric field amplitude of \( 45 \, \text{V/m} \). What is the magnetic field amplitude? (Given \( c = 3 \times 10^8 \, \text{m/s} \))

Using \( B_0 = \frac{E_0}{c} \), we have \( B_0 = \frac{45}{3 \times 10^8} = 1.5 \times 10^{-7} \, \text{T} \).

\( 1 \times 10^{-7} \, \text{T} \)
\( 1.2 \times 10^{-7} \, \text{T} \)
\( 1.3 \times 10^{-7} \, \text{T} \)
\( 1.5 \times 10^{-7} \, \text{T} \)
4

In a charging capacitor, if the conduction current in the wires is \( 3 \, \text{A} \), what is the displacement current between the plates?

The document states that inside a charging capacitor, the displacement current equals the conduction current in the wires. Thus, \( i_d = 3 \, \text{A} \).

3 A
1.5 A
6 A
0 A
1

An electromagnetic wave in vacuum has a wavelength of \( 12 \, \text{m} \). What is its frequency? (Given \( c = 3 \times 10^8 \, \text{m/s} \))

Using \( v \lambda = c \), we have \( v = \frac{c}{\lambda} = \frac{3 \times 10^8}{12} = 2.5 \times 10^7 \, \text{Hz} \).

\( 2 \times 10^7 \, \text{Hz} \)
\( 2.25 \times 10^7 \, \text{Hz} \)
\( 2.5 \times 10^7 \, \text{Hz} \)
\( 3 \times 10^7 \, \text{Hz} \)
3

What is the wavelength range of infrared waves as per the document?

The document states that infrared waves range from \( 1 \, \text{mm} \) to \( 700 \, \text{nm} \).

\( 400 \, \text{nm} \) to \( 0.6 \, \text{nmol} \)
\( 10 \, \text{nm} \) to \( 10^{-4} \, \text{nm} \)
\( > 0.1 \, \text{m} \)
\( 1 \, \text{mm} \) to \( 700 \, \text{nm} \)
4

What type of electromagnetic waves did Hertz produce in his experiment?

The document mentions that Hertz produced electromagnetic waves in the low-frequency region, specifically radio waves, in 1887.

Radio waves
Microwaves
Visible light
Gamma rays
1

Which type of electromagnetic waves are produced by the rapid acceleration and deceleration of electrons in aerials?

The document states that radio waves are produced by the rapid acceleration and deceleration of electrons in aerials.

Microwaves
Radio waves
Infrared waves
Ultraviolet waves
2

In a circuit with a capacitor, if the rate of change of electric flux is \( 2 \times 10^{11} \, \text{Vm/s} \), what is the displacement current? (Given \( \varepsilon_0 = 8.85 \times 10^{-12} \, \text{F/m} \))

Displacement current \( i_d = \varepsilon_0 \frac{d \Phi_E}{dt} \). Substituting the values, \( i_d = (8.85 \times 10^{-12}) \times (2 \times 10^{11}) = 1.77 \, \text{A} \).

1.77 A
0.885 A
3.54 A
4.42 A
1

Why are radio waves effective for long-distance communication?

Radio waves have long wavelengths allowing them to diffract around obstacles and reflect off the ionosphere, enabling transmission over long distances.

Short wavelengths
High energy
Visible spectrum
Diffraction and reflection
4

Why are microwaves used in domestic microwave ovens?

The document explains that microwaves are used because their frequency matches the resonant frequency of water molecules, efficiently transferring energy to heat food.

They have long wavelengths
Their frequency matches water molecule resonance
They emit visible light
They are absorbed by air
2

Which frequency range corresponds to short wave bands used for radio communication?

The document states that frequencies up to \( 54 \, \text{MHz} \) are used for short wave bands in radio communication.

\( 88 \, \text{MHz} \) to \( 108 \, \text{MHz} \)
\( 530 \, \text{kHz} \) to \( 1710 \, \text{kHz} \)
Up to \( 54 \, \text{MHz} \)
\( 4 \times 10^{14} \, \text{Hz} \) to \( 7 \times 10^{14} \, \text{Hz} \)
3

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