Electromagnetic Waves Chapter-Wise Test 9

Correct answer Carries: 4.

Wrong Answer Carries: -1.

What is the wavelength of an electromagnetic wave in vacuum with frequency \( 50 \, \text{MHz} \)? (Given \( c = 3 \times 10^8 \, \text{m/s} \))

Using \( v \lambda = c \), we have \( \lambda = \frac{c}{v} = \frac{3 \times 10^8}{50 \times 10^6} = 6 \, \text{m} \).

4 m
6 m
8 m
10 m
2

What type of electromagnetic waves did Maxwell predict before their experimental discovery?

The document mentions that Maxwell predicted the existence of electromagnetic waves, which were later confirmed to include light, radio waves, and others, but initially, they were general EM waves.

Electromagnetic waves including light
Only visible light
Only gamma rays
Only infrared waves
1

An electromagnetic wave in vacuum has an electric field given by \( E_x = 150 \sin(5 \times 10^3 z - 1.5 \times 10^{12} t) \, \text{V/m} \). What is the angular frequency \( \omega \)?

Comparing with \( E_x = E_0 \sin(kz - \omega t) \), we have \( \omega = 1.5 \times 10^{12} \, \text{rad/s} \).

\( 1.0 \times 10^{12} \, \text{rad/s} \)
\( 1.5 \times 10^{12} \, \text{rad/s} \)
\( 2.0 \times 10^{12} \, \text{rad/s} \)
\( 2.5 \times 10^{12} \, \text{rad/s} \)
2

What is the approximate wavelength range of radio waves as per the document?

The document states that radio waves have wavelengths greater than \( 0.1 \, \text{m} \), with long radio waves up to \( 10^6 \, \text{m} \).

\( 1 \, \text{mm} \) to \( 700 \, \text{nm} \)
\( > 0.1 \, \text{m} \)
\( 10^{-10} \, \text{m} \) to \( 10^{-14} \, \text{m} \)
\( 400 \, \text{nm} \) to \( 0.6 \, \text{nm} \)
2

What inconsistency did Maxwell notice in Ampere's circuital law before introducing displacement current?

Maxwell noticed that Ampere's law gave different results for the magnetic field outside a capacitor depending on the surface used, leading to a contradiction when calculating the field at a point.

Different magnetic fields for different surfaces
Zero magnetic field everywhere
Inability to calculate electric fields
Lack of symmetry with Faraday's Law
1

According to Maxwell's equations, what does the equation \( \oint \mathbf{B} \cdot \mathrm{d} \mathbf{A} = 0 \) imply?

This is Gauss's Law for magnetism, which implies that there are no magnetic monopoles, as the net magnetic flux through a closed surface is zero.

No magnetic monopoles exist
Magnetic fields are always zero
Electric fields generate magnetic fields
Magnetic flux is proportional to charge
1

Why are ultraviolet lamps used in water purifiers?

UV lamps are used to kill germs in water purifiers due to their ability to damage living organisms, as mentioned in the document.

To heat the water
To detect impurities
To kill germs
To emit visible light
3

Why are infrared waves used in remote switches of household electronic systems?

The document mentions that infrared waves are emitted by electronic devices like LEDs and are widely used in remote switches due to their ability to transmit signals effectively over short distances.

They have long wavelengths
They transmit signals effectively
They are visible to the eye
They heat the devices
2

What is the approximate wavelength range of visible light?

The document states that visible light ranges from about \( 700 \, \text{nm} \) to \( 400 \, \text{nm} \).

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

Why are infrared detectors used in Earth satellites?

Infrared detectors are used for military purposes and to observe crop growth, as stated in the document.

To detect radio waves
To measure ultraviolet radiation
To detect gamma rays
For military purposes and crop observation
4

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