Electromagnetic Waves Chapter-Wise Test 8

Correct answer Carries: 4.

Wrong Answer Carries: -1.

In the context of electromagnetic theory, what fundamental principle explains why a changing electric field can generate a magnetic field?

The Ampere-Maxwell law states that a changing electric field (via displacement current) acts as a source of a magnetic field, complementing the conduction current's role in generating magnetic fields.

Ampere-Maxwell law
Faraday’s law of induction
Gauss’s law for electricity
Gauss’s law for magnetism
1

What is a common method to detect visible light as per the document?

The document lists the human eye, photocells, and photographic film as detectors of visible light. The human eye is the most common.

Thermopiles
Geiger tubes
The human eye
Receiver's aerials
3

In an electromagnetic wave, if the electric field oscillates along the \( y \)-axis and the wave propagates along the \( x \)-axis, what is the direction of the magnetic field?

In an EM wave, \( \mathbf{E} \), \( \mathbf{B} \), and the direction of propagation are perpendicular. If \( \mathbf{E} \) is along \( y \)-axis and propagation is along \( x \)-axis, then \( \mathbf{B} \) must be along \( z \)-axis (\( \mathbf{E} \times \mathbf{B} \) gives propagation direction).

\( z \)-axis
\( x \)-axis
\( y \)-axis
None of these
1

Why are microwaves used in speed guns to time fast-moving objects?

The document mentions that microwaves are used in radar systems (like speed guns) due to their short wavelengths, which allow precise measurements.

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

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

A capacitor in a circuit has a conduction current of \( 2.5 \, \text{A} \) in the wires. What is the displacement current between the plates?

The document states that in a charging capacitor, the displacement current between the plates equals the conduction current in the wires, so \( i_d = 2.5 \, \text{A} \).

2.5 A
1.25 A
5 A
0 A
1

Who first experimentally demonstrated the existence of electromagnetic waves?

Heinrich Rudolf Hertz, in 1887, was the first to produce and detect electromagnetic waves, verifying Maxwell's predictions.

James Clerk Maxwell
Guglielmo Marconi
Heinrich Rudolf Hertz
Jagdish Chandra Bose
3

What physical principle explains why electromagnetic waves can carry energy over long distances?

The oscillating electric and magnetic fields of electromagnetic waves carry energy in the form of electromagnetic energy flux, described by the Poynting vector, enabling long-distance energy transfer.

Static field interactions
Mechanical wave interference
Oscillating electric and magnetic fields
Constant wavelength modulation
3

Gamma rays are used in medicine primarily for what purpose?

The document mentions that gamma rays are used in medicine to destroy cancer cells.

Heating tissues
Imaging bones
Destroying cancer cells
Killing germs in water
3

An electromagnetic wave in vacuum has a frequency of \( 75 \, \text{MHz} \). What is its wavelength? (Given \( c = 3 \times 10^8 \, \text{m/s} \))

Using \( v \lambda = c \), we have \( \lambda = \frac{c}{v} = \frac{3 \times 10^8}{75 \times 10^6} = 4 \, \text{m} \).

2 m
4 m
6 m
8 m
2

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