Electromagnetic Waves Practice Questions
Willer Academy - English Medium
Previous Year & Expected Questions for Bihar Board
Instructions: This practice set contains 10 Multiple Choice Questions, 5 Subjective Questions, and 5 Numerical Problems covering all topics of electromagnetic waves. Try to solve all questions before checking the answers.
Multiple Choice Questions (10 Questions)
1 Mark Each1. Which of the following has the highest frequency?
Answer: (c) X-rays
Explanation: X-rays have higher frequency compared to radio waves, microwaves, and infrared waves in the electromagnetic spectrum.
Explanation: X-rays have higher frequency compared to radio waves, microwaves, and infrared waves in the electromagnetic spectrum.
2. The electromagnetic waves used in satellite communication are:
Answer: (b) Microwaves
Explanation: Microwaves are used in satellite communication because they can penetrate through the atmosphere with minimal absorption.
Explanation: Microwaves are used in satellite communication because they can penetrate through the atmosphere with minimal absorption.
3. Which of the following electromagnetic waves is used for cancer treatment?
Answer: (b) Gamma rays
Explanation: Gamma rays are used in radiotherapy to destroy cancer cells.
Explanation: Gamma rays are used in radiotherapy to destroy cancer cells.
4. The speed of electromagnetic waves in vacuum is:
Answer: (b) 3 × 10^8 m/s
Explanation: The speed of all electromagnetic waves in vacuum is constant and equal to 3 × 10^8 m/s.
Explanation: The speed of all electromagnetic waves in vacuum is constant and equal to 3 × 10^8 m/s.
5. Which of the following is NOT an electromagnetic wave?
Answer: (b) Sound waves
Explanation: Sound waves are mechanical waves that require a medium to propagate, while electromagnetic waves can travel through vacuum.
Explanation: Sound waves are mechanical waves that require a medium to propagate, while electromagnetic waves can travel through vacuum.
6. The electromagnetic waves used for sterilization of medical instruments are:
Answer: (c) Ultraviolet waves
Explanation: UV rays have germicidal properties and are used to sterilize medical instruments and purify water.
Explanation: UV rays have germicidal properties and are used to sterilize medical instruments and purify water.
7. Which of the following has the longest wavelength?
Answer: (c) Radio waves
Explanation: Radio waves have the longest wavelength in the electromagnetic spectrum.
Explanation: Radio waves have the longest wavelength in the electromagnetic spectrum.
8. The electromagnetic waves used in remote controls of electronic devices are:
Answer: (b) Infrared waves
Explanation: Remote controls for TVs, ACs, etc., use infrared waves to transmit signals.
Explanation: Remote controls for TVs, ACs, etc., use infrared waves to transmit signals.
9. The relation between frequency (ν) and wavelength (λ) of an electromagnetic wave is:
Answer: (a) ν = c/λ
Explanation: The relationship between frequency and wavelength is given by c = νλ, where c is the speed of light. Therefore, ν = c/λ.
Explanation: The relationship between frequency and wavelength is given by c = νλ, where c is the speed of light. Therefore, ν = c/λ.
10. Which electromagnetic waves are absorbed by the ozone layer?
Answer: (b) Ultraviolet waves
Explanation: The ozone layer absorbs harmful ultraviolet radiation from the sun, protecting life on Earth.
Explanation: The ozone layer absorbs harmful ultraviolet radiation from the sun, protecting life on Earth.
Subjective Questions (5 Questions)
3-5 Marks Each1. What are electromagnetic waves? Write down the main characteristics of electromagnetic waves.
Answer:
Electromagnetic waves are waves that consist of oscillating electric and magnetic fields perpendicular to each other and to the direction of propagation.
Characteristics:
- They can travel through vacuum.
- They travel at the speed of light (3 × 10^8 m/s) in vacuum.
- They are transverse in nature.
- They do not require a medium for propagation.
- They obey the wave equation: c = νλ.
- They carry energy and momentum.
- They can be reflected, refracted, diffracted, and polarized.
Electromagnetic waves are waves that consist of oscillating electric and magnetic fields perpendicular to each other and to the direction of propagation.
Characteristics:
- They can travel through vacuum.
- They travel at the speed of light (3 × 10^8 m/s) in vacuum.
- They are transverse in nature.
- They do not require a medium for propagation.
- They obey the wave equation: c = νλ.
- They carry energy and momentum.
- They can be reflected, refracted, diffracted, and polarized.
2. Write the electromagnetic spectrum in order of increasing frequency and mention one use of each type of wave.
Answer:
The electromagnetic spectrum in order of increasing frequency:
1. Radio waves: Used in radio and television broadcasting.
2. Microwaves: Used in microwave ovens and satellite communication.
3. Infrared waves: Used in remote controls and thermal imaging.
4. Visible light: Enables vision and photography.
5. Ultraviolet waves: Used for sterilization and in black lights.
6. X-rays: Used in medical imaging and security screening.
7. Gamma rays: Used in cancer treatment and sterilization of medical equipment.
The electromagnetic spectrum in order of increasing frequency:
1. Radio waves: Used in radio and television broadcasting.
2. Microwaves: Used in microwave ovens and satellite communication.
3. Infrared waves: Used in remote controls and thermal imaging.
4. Visible light: Enables vision and photography.
5. Ultraviolet waves: Used for sterilization and in black lights.
6. X-rays: Used in medical imaging and security screening.
7. Gamma rays: Used in cancer treatment and sterilization of medical equipment.
3. Differentiate between electromagnetic waves and mechanical waves.
Answer:
| Electromagnetic Waves | Mechanical Waves |
|---|---|
| Can propagate through vacuum | Require a material medium |
| Consist of electric and magnetic fields | Consist of oscillations of particles |
| Transverse in nature | Can be transverse or longitudinal |
| Travel at speed of light (3×10^8 m/s) | Travel at speed of sound (approx. 330 m/s in air) |
| Examples: Light, radio waves, X-rays | Examples: Sound waves, water waves |
4. Explain how electromagnetic waves are produced. Describe Hertz experiment to demonstrate the existence of electromagnetic waves.
Answer:
Production of electromagnetic waves:
Electromagnetic waves are produced by accelerated charged particles. When a charged particle accelerates, it produces changing electric and magnetic fields, which propagate as electromagnetic waves.
Hertz Experiment:
Heinrich Hertz conducted an experiment in 1887 to demonstrate the existence of electromagnetic waves predicted by Maxwell.
Apparatus:
- A high voltage induction coil connected to two metallic spheres with a small gap (transmitter)
- A circular wire with a small gap (receiver)
Procedure:
When high voltage was applied to the transmitter, sparks were produced across the gap. Simultaneously, tiny sparks were observed in the gap of the receiver, which was placed some distance away.
Conclusion:
The sparks in the receiver were caused by electromagnetic waves generated by the oscillating charges in the transmitter. This experiment confirmed the existence of electromagnetic waves and verified Maxwell's theory.
Production of electromagnetic waves:
Electromagnetic waves are produced by accelerated charged particles. When a charged particle accelerates, it produces changing electric and magnetic fields, which propagate as electromagnetic waves.
Hertz Experiment:
Heinrich Hertz conducted an experiment in 1887 to demonstrate the existence of electromagnetic waves predicted by Maxwell.
Apparatus:
- A high voltage induction coil connected to two metallic spheres with a small gap (transmitter)
- A circular wire with a small gap (receiver)
Procedure:
When high voltage was applied to the transmitter, sparks were produced across the gap. Simultaneously, tiny sparks were observed in the gap of the receiver, which was placed some distance away.
Conclusion:
The sparks in the receiver were caused by electromagnetic waves generated by the oscillating charges in the transmitter. This experiment confirmed the existence of electromagnetic waves and verified Maxwell's theory.
5. State Maxwell's equations and explain their significance in the theory of electromagnetic waves.
Answer:
Maxwell's equations are a set of four fundamental equations that describe how electric and magnetic fields are generated and altered by each other and by charges and currents.
The four equations are:
1. Gauss's Law for Electricity: ∮E·dA = Q/ε₀
Relates electric field to the charge distribution.
2. Gauss's Law for Magnetism: ∮B·dA = 0
States that there are no magnetic monopoles.
3. Faraday's Law of Induction: ∮E·dl = -dΦ_B/dt
Relates changing magnetic field to induced electric field.
4. Ampere-Maxwell Law: ∮B·dl = μ₀I + μ₀ε₀dΦ_E/dt
Relates magnetic field to electric current and changing electric field.
Significance:
- These equations unified electricity and magnetism into a single theory.
- They predicted the existence of electromagnetic waves.
- They showed that light is an electromagnetic wave.
- They form the foundation of classical electromagnetism.
Maxwell's equations are a set of four fundamental equations that describe how electric and magnetic fields are generated and altered by each other and by charges and currents.
The four equations are:
1. Gauss's Law for Electricity: ∮E·dA = Q/ε₀
Relates electric field to the charge distribution.
2. Gauss's Law for Magnetism: ∮B·dA = 0
States that there are no magnetic monopoles.
3. Faraday's Law of Induction: ∮E·dl = -dΦ_B/dt
Relates changing magnetic field to induced electric field.
4. Ampere-Maxwell Law: ∮B·dl = μ₀I + μ₀ε₀dΦ_E/dt
Relates magnetic field to electric current and changing electric field.
Significance:
- These equations unified electricity and magnetism into a single theory.
- They predicted the existence of electromagnetic waves.
- They showed that light is an electromagnetic wave.
- They form the foundation of classical electromagnetism.
Numerical Problems (5 Questions)
3-5 Marks Each1. Calculate the wavelength of electromagnetic waves of frequency 3 × 10^9 Hz. (Speed of light = 3 × 10^8 m/s)
Solution:
Given: Frequency (ν) = 3 × 10^9 Hz, Speed of light (c) = 3 × 10^8 m/s
Using the formula: c = νλ
⇒ λ = c/ν
⇒ λ = (3 × 10^8) / (3 × 10^9)
⇒ λ = 0.1 m
Answer: The wavelength is 0.1 m.
Given: Frequency (ν) = 3 × 10^9 Hz, Speed of light (c) = 3 × 10^8 m/s
Using the formula: c = νλ
⇒ λ = c/ν
⇒ λ = (3 × 10^8) / (3 × 10^9)
⇒ λ = 0.1 m
Answer: The wavelength is 0.1 m.
2. The magnetic field in a plane electromagnetic wave is given by B = 2 × 10^-7 sin(0.5 × 10^3 x + 1.5 × 10^11 t) T. Calculate the wavelength and frequency of the wave.
Solution:
The wave equation is: B = B₀ sin(kx + ωt)
Comparing with given equation: B = 2 × 10^-7 sin(0.5 × 10^3 x + 1.5 × 10^11 t)
We have:
Wave number (k) = 0.5 × 10^3 m⁻¹ = 500 m⁻¹
Angular frequency (ω) = 1.5 × 10^11 rad/s
Wavelength: λ = 2π/k = 2 × 3.14 / 500 = 0.01256 m
Frequency: ν = ω/(2π) = (1.5 × 10^11) / (2 × 3.14) = 2.39 × 10^10 Hz
Answer: Wavelength = 0.01256 m, Frequency = 2.39 × 10^10 Hz
The wave equation is: B = B₀ sin(kx + ωt)
Comparing with given equation: B = 2 × 10^-7 sin(0.5 × 10^3 x + 1.5 × 10^11 t)
We have:
Wave number (k) = 0.5 × 10^3 m⁻¹ = 500 m⁻¹
Angular frequency (ω) = 1.5 × 10^11 rad/s
Wavelength: λ = 2π/k = 2 × 3.14 / 500 = 0.01256 m
Frequency: ν = ω/(2π) = (1.5 × 10^11) / (2 × 3.14) = 2.39 × 10^10 Hz
Answer: Wavelength = 0.01256 m, Frequency = 2.39 × 10^10 Hz
3. A radio station broadcasts at a frequency of 1 MHz. What is the wavelength of the radio waves? (Speed of light = 3 × 10^8 m/s)
Solution:
Given: Frequency (ν) = 1 MHz = 1 × 10^6 Hz, Speed of light (c) = 3 × 10^8 m/s
Using the formula: c = νλ
⇒ λ = c/ν
⇒ λ = (3 × 10^8) / (1 × 10^6)
⇒ λ = 300 m
Answer: The wavelength is 300 m.
Given: Frequency (ν) = 1 MHz = 1 × 10^6 Hz, Speed of light (c) = 3 × 10^8 m/s
Using the formula: c = νλ
⇒ λ = c/ν
⇒ λ = (3 × 10^8) / (1 × 10^6)
⇒ λ = 300 m
Answer: The wavelength is 300 m.
4. The amplitude of the magnetic field part of a harmonic electromagnetic wave in vacuum is B₀ = 510 nT. What is the amplitude of the electric field part of the wave?
Solution:
Given: B₀ = 510 nT = 510 × 10⁻⁹ T = 5.1 × 10⁻⁷ T
Speed of light (c) = 3 × 10^8 m/s
For electromagnetic waves in vacuum: E₀/B₀ = c
⇒ E₀ = c × B₀
⇒ E₀ = (3 × 10^8) × (5.1 × 10⁻⁷)
⇒ E₀ = 153 N/C
Answer: The amplitude of the electric field is 153 N/C.
Given: B₀ = 510 nT = 510 × 10⁻⁹ T = 5.1 × 10⁻⁷ T
Speed of light (c) = 3 × 10^8 m/s
For electromagnetic waves in vacuum: E₀/B₀ = c
⇒ E₀ = c × B₀
⇒ E₀ = (3 × 10^8) × (5.1 × 10⁻⁷)
⇒ E₀ = 153 N/C
Answer: The amplitude of the electric field is 153 N/C.
5. A plane electromagnetic wave of frequency 25 MHz travels in free space along the x-direction. At a particular point in space and time, E = 6.3 j V/m. What is B at this point?
Solution:
Given: E = 6.3 j V/m, c = 3 × 10^8 m/s
For electromagnetic waves: |E|/|B| = c
⇒ |B| = |E|/c
⇒ |B| = 6.3 / (3 × 10^8)
⇒ |B| = 2.1 × 10⁻⁸ T
Since the wave is propagating along x-direction and E is along y-direction, B must be along z-direction (as E, B, and direction of propagation are mutually perpendicular).
Answer: B = 2.1 × 10⁻⁸ k T
Given: E = 6.3 j V/m, c = 3 × 10^8 m/s
For electromagnetic waves: |E|/|B| = c
⇒ |B| = |E|/c
⇒ |B| = 6.3 / (3 × 10^8)
⇒ |B| = 2.1 × 10⁻⁸ T
Since the wave is propagating along x-direction and E is along y-direction, B must be along z-direction (as E, B, and direction of propagation are mutually perpendicular).
Answer: B = 2.1 × 10⁻⁸ k T
Practice these questions thoroughly for your Bihar Board examination. All the best!
Electromagnetic Waves Practice Test
Willer Academy - English Medium
Time: 60 Minutes | Maximum Marks: 50
Instructions: This test contains 10 Multiple Choice Questions, 5 Subjective Questions, and 5 Numerical Problems. Answer all questions in the given time.
Multiple Choice Questions (10 Questions)
1 Mark Each1. Which electromagnetic waves are used in night vision equipment?
2. The electromagnetic waves used in RADAR systems are:
3. Which of the following has the shortest wavelength?
4. The electromagnetic waves used for checking mineral samples are:
5. Which of the following statements is true for electromagnetic waves?
6. The electromagnetic waves used in photography at night and in fog are:
7. Which electromagnetic waves are used to study the structure of molecules?
8. The energy of an electromagnetic wave is proportional to:
9. Which electromagnetic waves are used in burglar alarms?
10. The electromagnetic waves that cause sunburn are:
Subjective Questions (5 Questions)
3-5 Marks Each1. Explain the phenomenon of polarization of electromagnetic waves. What does it indicate about the nature of these waves?
2. Describe the uses of different regions of the electromagnetic spectrum in medical field.
3. What is the significance of displacement current in Maxwell's equations? How did it lead to the prediction of electromagnetic waves?
4. Explain why electromagnetic waves are said to transport energy and momentum.
5. Compare the properties of electromagnetic waves and sound waves.
Numerical Problems (5 Questions)
3-5 Marks Each1. A TV tower has a height of 100 m. What is the maximum distance up to which the TV transmission can be received? (Radius of Earth = 6.4 × 10^6 m)
2. The amplitude of the magnetic field of an electromagnetic wave is 2 × 10^-6 T. Calculate the amplitude of the electric field. (Speed of light = 3 × 10^8 m/s)
3. A radio can tune in to any station in the 7.5 MHz to 12 MHz band. What is the corresponding wavelength band? (Speed of light = 3 × 10^8 m/s)
4. The electric field in a plane electromagnetic wave is given by E = 120 sin(1.6 × 10^3 x + 4.8 × 10^11 t) j V/m. Calculate the amplitude of the magnetic field.
5. A plane electromagnetic wave of frequency 30 MHz travels in free space. Calculate its wavelength. (Speed of light = 3 × 10^8 m/s)
Submit your answers to your teacher for evaluation. All the best for your preparation!
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