Electromagnetic Waves Chapter-Wise Test 2

Correct answer Carries: 4.

Wrong Answer Carries: -1.

What is the frequency range of visible light?

Visible light ranges from about \( 4 \times 10^{14} \, \text{Hz} \) to \( 7 \times 10^{14} \, \text{Hz} \), as stated in the document.

\( 10^9 \, \text{Hz} \) to \( 10^{11} \, \text{Hz} \)
\( 4 \times 10^{14} \, \text{Hz} \) to \( 7 \times 10^{14} \, \text{Hz} \)
\( 10^{16} \, \text{Hz} \) to \( 10^{18} \, \text{Hz} \)
\( 500 \, \text{kHz} \) to \( 1000 \, \text{MHz} \)
2

Why are X-rays used in medicine to treat certain forms of cancer?

The document explains that X-rays can damage or destroy living tissues, which makes them useful for targeting and destroying cancer cells.

They emit visible light
They heat tissues
They enhance cell growth
They destroy cancer cells
4

In electromagnetic wave propagation, what ensures that the electric and magnetic fields sustain each other?

The mutual induction described by Maxwell’s equations (Faraday’s law and Ampere-Maxwell law) ensures that a changing electric field induces a magnetic field, and vice versa, sustaining wave propagation.

Mutual induction via Maxwell’s equations
Constant electric field strength
Presence of a material medium
Static magnetic fields
1

Which of the following is used to detect X-rays?

The document lists photographic film, Geiger tubes, and ionization chambers as detectors for X-rays. Geiger tubes are a common choice.

Thermopiles
Photocells
Geiger tubes
Receiver's aerials
3

X-rays are typically used in medicine for which purpose?

X-rays are used as a diagnostic tool in medicine and for treating certain forms of cancer, as mentioned in the document.

Heating tissues
Killing germs
Detecting infrared radiation
Diagnosis and cancer treatment
4

Why are infrared waves detected in applications monitoring crop growth?

Infrared waves are reflected or emitted by plants based on their health and water content, allowing detectors to assess crop conditions through variations in infrared signatures.

High penetration
Visible spectrum
Plant reflectivity
Thermal heating
3

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

The document states that ultraviolet rays range from about \( 400 \, \text{nm} \) to \( 0.6 \, \text{nm} \).

\( > 0.1 \, \text{m} \)
\( 0.1 \, \text{m} \) to \( 1 \, \text{mm} \)
\( 1 \, \text{mm} \) to \( 700 \, \text{nm} \)
\( 400 \, \text{nm} \) to \( 0.6 \, \text{nm} \)
4

An electromagnetic wave has a magnetic field amplitude of \( B_0 = 8 \times 10^{-8} \, \text{T} \). What is the electric field amplitude? (Given \( c = 3 \times 10^8 \, \text{m/s} \))

Using \( E_0 = B_0 c \), we have \( E_0 = (8 \times 10^{-8}) \times (3 \times 10^8) = 24 \, \text{V/m} \).

16 V/m
18 V/m
20 V/m
24 V/m
4

In electromagnetic theory, what explains the constant ratio of electric to magnetic field amplitudes in a wave?

The ratio \( \frac{E_0}{B_0} = c \), where \( c \) is the speed of light, arises from Maxwell’s equations, ensuring energy conservation and wave propagation consistency in vacuum.

Frequency variation
Medium properties
Maxwell’s equations
Static fields
3

Why are UV rays harmful in large quantities?

The document mentions that UV rays in large quantities have harmful effects on humans, such as damaging skin cells and inducing excessive melanin production.

They heat the skin excessively
They emit visible light
They have harmful effects on humans
They enhance thermal motion
3

A parallel plate capacitor with plate area \( A = 0.01 \, \text{m}^2 \) and separation \( d = 2 \, \text{mm} \) is being charged at a rate of \( \frac{dQ}{dt} = 0.5 \, \text{A} \). What is the displacement current between the plates? (Given \( \varepsilon_0 = 8.85 \times 10^{-12} \, \text{F/m} \))

Displacement current \( i_d = \varepsilon_0 \frac{d \Phi_E}{dt} \). Since \( \Phi_E = \frac{Q}{\varepsilon_0} \), we have \( \frac{d \Phi_E}{dt} = \frac{1}{\varepsilon_0} \frac{dQ}{dt} \). But in a capacitor, \( i_d = \frac{dQ}{dt} \). Thus, \( i_d = 0.5 \, \text{A} \).

0.25 A
0.5 A
0.75 A
1.0 A
2

What makes electromagnetic waves capable of carrying energy over long distances?

The document highlights that electromagnetic waves carry energy from one place to another, a capability stemming from their oscillating electric and magnetic fields.

Their dependence on a medium
Their constant wavelength
Their variable frequency
Their oscillating electric and magnetic fields
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 helps maintain Earth's average temperature.

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

Why does the absence of conduction current in certain regions necessitate the concept of displacement current?

In regions without conduction current, such as between capacitor plates or in free space, a changing electric field still generates a magnetic field via displacement current, maintaining consistency in electromagnetic theory.

To explain magnetic field generation
To eliminate electric fields
To create static fields
To cancel conduction currents
1

An electromagnetic wave in vacuum has a wavelength of \( 5 \, \text{m} \). What is its frequency? (Given \( c = 3 \times 10^8 \, \text{m/s} \))

Using \( v \lambda = c \), we have \( v = \frac{c}{\lambda} = \frac{3 \times 10^8}{5} = 6 \times 10^7 \, \text{Hz} \).

\( 3 \times 10^7 \, \text{Hz} \)
\( 5 \times 10^7 \, \text{Hz} \)
\( 6 \times 10^7 \, \text{Hz} \)
\( 9 \times 10^7 \, \text{Hz} \)
3

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