Electromagnetic Waves Chapter-Wise Test 21

Correct answer Carries: 4.

Wrong Answer Carries: -1.

Which Maxwell equation describes the generation of an electric field by a changing magnetic field?

Faraday's Law, as expressed in Maxwell's equations, states that a changing magnetic field induces an electric field: \( \oint \mathbf{E} \cdot \mathrm{d} \mathbf{l} = -\frac{\mathrm{d} \Phi_B}{\mathrm{d} t} \).

Gauss's Law for electricity
Gauss's Law for magnetism
Faraday's Law
Ampere-Maxwell Law
3

In the context of electromagnetic waves, what physical characteristic distinguishes radio waves from gamma rays?

Radio waves and gamma rays differ primarily in their wavelengths (or frequencies), with radio waves having much longer wavelengths (lower frequencies) than gamma rays, which have very short wavelengths.

Speed of propagation
Wavelength
Direction of propagation
Medium of travel
2

Why are X-rays used as a diagnostic tool in medicine?

The document explains that X-rays can penetrate tissues and are used to image internal structures, making them effective as a diagnostic tool.

They heat tissues
They emit visible light
They kill germs
They penetrate tissues for imaging
4

Why are UV rays used in LASIK eye surgery?

The document mentions that due to their shorter wavelengths, UV rays can be focused into narrow beams, making them suitable for high-precision applications like LASIK eye surgery.

They heat the cornea
They emit visible light
They can be focused into narrow beams
They penetrate deeper into tissues
3

Why are X-rays suitable for imaging bones in medical diagnostics?

X-rays have high penetrating power due to their short wavelengths, allowing them to pass through soft tissues but be absorbed by denser bones, creating clear images.

They heat tissues
They emit visible light
They are reflected by bones
They penetrate soft tissues
4

Why does the speed of electromagnetic waves in a medium depend on the medium’s properties?

The speed of electromagnetic waves in a medium is determined by the medium’s permittivity (\( \varepsilon \)) and permeability (\( \mu \)), as \( v = \frac{1}{\sqrt{\mu \varepsilon}} \), which modifies the wave’s propagation characteristics.

Dependence on permittivity and permeability
Dependence on frequency
Constant speed in all media
Absence of electric fields
1

What is a common method to detect infrared waves as per the document?

The document lists thermopiles, bolometers, and infrared photographic film as detectors for infrared waves. Bolometers are a common choice.

Geiger tubes
Receiver's aerials
Bolometers
Photocells
3

What makes electromagnetic waves different from other waves discussed in the document?

The document notes that electromagnetic waves differ from other waves because they involve no material medium for propagation—they are oscillations of electric and magnetic fields.

They have higher frequencies
They are always visible
They travel slower
They require no material medium
4

What is the role of displacement current in Maxwell's generalization of Ampere's law?

Maxwell introduced displacement current to account for the magnetic field produced by a time-varying electric field, ensuring consistency in Ampere's circuital law when applied to capacitors.

It produces a magnetic field due to a changing electric field
It accounts for conduction current only
It eliminates the need for conduction current
It opposes the magnetic field in all cases
1

Cellular phones use which type of electromagnetic waves for voice communication?

The document mentions that cellular phones use radio waves in the ultrahigh frequency (UHF) band for voice communication.

Microwaves
Infrared waves
Radio waves
Ultraviolet waves
3

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