Electromagnetic Waves Chapter-Wise Test 14

Correct answer Carries: 4.

Wrong Answer Carries: -1.

What is the frequency range of the FM radio band?

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 \( 890 \, \text{MHz} \)
\( 500 \, \text{kHz} \) to \( 1000 \, \text{MHz} \)
\( 88 \, \text{MHz} \) to \( 108 \, \text{MHz} \)
4

Why are infrared waves important for maintaining Earth's average temperature?

The document explains that infrared radiation is trapped by greenhouse gases, contributing to the greenhouse effect, which maintains Earth's warmth.

They reflect sunlight
They emit UV radiation
They contribute to the greenhouse effect
They cool the atmosphere
3

Why can’t one get tanned through ordinary glass windows?

The document explains that UV radiation, which causes tanning, is absorbed by ordinary glass, preventing it from passing through.

Glass emits infrared radiation
Glass reflects visible light
Glass scatters UV radiation
Glass absorbs UV radiation
4

Infrared waves contribute to Earth's warmth through which effect?

The document explains that infrared radiation is trapped by greenhouse gases, contributing to Earth's warmth via the greenhouse effect.

Photoelectric effect
Ozone depletion
Greenhouse effect
Doppler effect
3

Why are microwaves suitable for use in radar systems?

Microwaves have short wavelengths that allow them to be focused into narrow beams, providing high resolution and precision for detecting objects in radar systems.

They have long wavelengths
They have short wavelengths for precision
They are absorbed by objects
They travel slower than light
2

Why do welders wear special glass goggles during welding?

The document explains that welding arcs produce large amounts of UV radiation, and special glass goggles protect the eyes from this harmful radiation.

To enhance visible light
To detect infrared radiation
To prevent heat exposure
To protect from UV radiation
4

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

Using \( v \lambda = c \), we have \( \lambda = \frac{c}{v} = \frac{3 \times 10^8}{20 \times 10^6} = 15 \, \text{m} \).

10 m
15 m
20 m
25 m
2

What does Gauss's Law for magnetism imply in Maxwell's equations?

Gauss's Law for magnetism, \( \oint \mathbf{B} \cdot \mathrm{d} \mathbf{A} = 0 \), 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 proportional to charge
Magnetic fields induce electric fields
Magnetic flux is always constant
1

What is one technological importance of electromagnetic waves mentioned in the document?

The document highlights that electromagnetic waves can carry energy, enabling technologies like radio and TV signals for broadcasting.

They require a medium to propagate
They have variable speeds
They are all visible
They carry energy for communication
4

Why can't visible light electromagnetic waves be produced by an oscillating circuit at \( 6 \times 10^{14} \, \text{Hz} \)?

The document explains that modern circuits can only achieve frequencies up to \( 10^{11} \, \text{Hz} \), far below the \( 6 \times 10^{14} \, \text{Hz} \) required for visible light.

Because circuits overheat at such frequencies
Because achievable frequencies are much lower
Because visible light requires a medium
Because magnetic fields cancel out
2

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