Electromagnetic Waves Chapter-Wise Test 17

Correct answer Carries: 4.

Wrong Answer Carries: -1.

What is the approximate wavelength range of gamma rays as per the document?

The document states that gamma rays have wavelengths from about \( 10^{-10} \, \text{m} \) to less than \( 10^{-14} \, \text{m} \).

\( 0.1 \, \text{m} \) to \( 1 \, \text{mm} \)
\( 1 \, \text{mm} \) to \( 700 \, \text{nm} \)
\( 400 \, \text{nm} \) to \( 0.6 \, \text{nm} \)
\( 10^{-10} \, \text{m} \) to \( 10^{-14} \, \text{m} \)
4

What property of electromagnetic waves explains why their speed in a medium is less than in vacuum?

The speed in a medium is reduced due to the medium’s permittivity (\( \varepsilon \)) and permeability (\( \mu \)), giving \( v = \frac{1}{\sqrt{\mu \varepsilon}} \), which is less than \( c \) because \( \varepsilon > \varepsilon_0 \) and \( \mu > \mu_0 \).

Frequency variation
Medium’s electric properties
Wavelength increase
Energy absorption
2

An electromagnetic wave in vacuum has a wavelength of \( 20 \, \text{m} \). What is its frequency? (Given \( c = 3 \times 10^8 \, \text{m/s} \))

Using \( v \lambda = c \), we have \( v = \frac{c}{\lambda} = \frac{3 \times 10^8}{20} = 1.5 \times 10^7 \, \text{Hz} \).

\( 1 \times 10^7 \, \text{Hz} \)
\( 1.25 \times 10^7 \, \text{Hz} \)
\( 1.5 \times 10^7 \, \text{Hz} \)
\( 2 \times 10^7 \, \text{Hz} \)
3

A capacitor is charged such that the electric flux through a surface between the plates changes at a rate of \( 5 \times 10^{10} \, \text{Vm/s} \). 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, \( i_d = (8.85 \times 10^{-12}) \times (5 \times 10^{10}) = 0.4425 \, \text{A} \).

0.4425 A
0.2213 A
0.8850 A
1.7700 A
1

Which frequency range corresponds to the FM radio band as per the document?

The document states that the FM radio band extends from \( 88 \, \text{MHz} \) to \( 108 \, \text{MHz} \).

\( 530 \, \text{kHz} \) to \( 1710 \, \text{kHz} \)
\( 54 \, \text{MHz} \) to \( 890 \, \text{MHz} \)
\( 88 \, \text{MHz} \) to \( 108 \, \text{MHz} \)
\( 500 \, \text{kHz} \) to \( 1000 \, \text{MHz} \)
3

Which of the following devices is used to detect infrared waves?

The document lists thermopiles, bolometers, and infrared photographic film as detectors of infrared waves.

Receiver's aerials
Photocells
Geiger tubes
Thermopiles
4

In the context of electromagnetic wave propagation, what ensures that the wave remains transverse?

Maxwell’s equations dictate that the electric and magnetic fields are perpendicular to each other and to the direction of propagation, ensuring that electromagnetic waves are transverse.

Presence of a medium
High frequency of oscillation
Perpendicular field orientation
Longitudinal field components
3

Why are ultraviolet rays more effective than visible light for sterilizing surfaces?

Ultraviolet rays have higher energy due to their shorter wavelengths, allowing them to penetrate and disrupt the DNA of microorganisms, which visible light cannot do effectively.

Visible light is more penetrating
Higher energy of UV rays
UV rays are less absorbed
Visible light heats surfaces
2

According to Maxwell's equations, what is the relationship between the speed of electromagnetic waves in vacuum and the constants \( \mu_0 \) and \( \varepsilon_0 \)?

The document states that the speed \( c \) of electromagnetic waves in vacuum is given by \( c = \frac{1}{\sqrt{\mu_0 \varepsilon_0}} \).

\( c = \frac{1}{\sqrt{\mu_0 \varepsilon_0}} \)
\( c = \sqrt{\mu_0 \varepsilon_0} \)
\( c = \mu_0 \varepsilon_0 \)
\( c = \frac{\mu_0}{\varepsilon_0} \)
1

An electromagnetic wave in vacuum has a frequency of \( 25 \, \text{MHz} \). What is its wavelength? (Given \( c = 3 \times 10^8 \, \text{m/s} \))

Using \( v \lambda = c \), we have \( \lambda = \frac{c}{v} = \frac{3 \times 10^8}{25 \times 10^6} = 12 \, \text{m} \).

8 m
12 m
15 m
18 m
2

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