Wave Motion

1. Which one of the following represents the correct order for the wavele

Which one of the following represents the correct order for the wavelengths of different waves ?

”Used
”Used
”Microwaves
”Used
This question was previously asked in
UPSC CISF-AC-EXE – 2023
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The correct order for the wavelengths of different waves is Used for AM radio > Used for FM radio > Microwaves > Infrared > Visible light. This corresponds to option B.
Electromagnetic waves are ordered by their wavelength (or equivalently, frequency). Longer wavelengths correspond to lower frequencies, and shorter wavelengths correspond to higher frequencies. The order of these waves from longest wavelength to shortest is: Radio waves (including AM and FM) > Microwaves > Infrared radiation > Visible light > Ultraviolet radiation > X-rays > Gamma rays. Within the radio wave spectrum, AM radio waves typically have longer wavelengths and lower frequencies than FM radio waves.
The approximate wavelength ranges are:
– AM Radio: Hundreds to thousands of meters
– FM Radio: A few meters
– Microwaves: Centimeters to decimeters (e.g., 1 cm to 1 meter)
– Infrared: Micrometers to millimeters (e.g., 700 nm to 1 mm)
– Visible Light: Nanometers (e.g., 400 nm – 700 nm)
Based on these ranges, the correct order from longest to shortest wavelength is AM Radio > FM Radio > Microwaves > Infrared > Visible Light.

2. Which electromagnetic radiation(s) is/are used to cook food?

Which electromagnetic radiation(s) is/are used to cook food?

Infrared radiation only
Microwave radiation only
Infrared and microwave radiations
All electromagnetic radiations
This question was previously asked in
UPSC CAPF – 2021
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Electromagnetic radiation is used in various forms for cooking food. Common examples include:
– Microwave ovens use microwave radiation to heat food. Microwaves are absorbed by water, fats, and sugars, causing them to vibrate and produce heat.
– Conventional ovens and grills use infrared radiation (thermal radiation) emitted by heating elements or flames to heat the food surface, and then heat is transferred into the food by conduction and convection.
Therefore, both infrared and microwave radiations are used in cooking. While visible light and other forms of EM radiation also carry energy and can potentially heat things, infrared and microwave are the primary forms utilized in common cooking appliances.
– Understand the different forms of electromagnetic radiation.
– Identify which forms of EM radiation are used in common cooking methods and appliances.
– Microwave ovens use microwaves.
– Ovens and grills use infrared radiation.
The electromagnetic spectrum includes radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays, in order of increasing frequency and energy. Cooking methods primarily utilize the energy transfer mechanisms of infrared radiation (heating surfaces) and microwave radiation (volumetric heating of polar molecules).

3. The radar used by police to check over-speeding vehicles works on the

The radar used by police to check over-speeding vehicles works on the principle of

Raman effect
Induction effect
Doppler effect
Coulomb effect
This question was previously asked in
UPSC CAPF – 2020
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The radar used by police to check over-speeding vehicles works on the principle of the Doppler effect.
The Doppler effect is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. Police radar guns emit radio waves towards a moving vehicle. When these waves reflect off the vehicle, their frequency is shifted. If the vehicle is moving towards the radar, the reflected waves have a higher frequency; if moving away, they have a lower frequency. The radar unit measures this frequency shift and calculates the vehicle’s speed based on the magnitude of the shift.
The Raman effect involves inelastic scattering of photons. The Induction effect relates to the production of an electromotive force across an electrical conductor in a changing magnetic field. The Coulomb effect describes the electrostatic interaction between charged particles. None of these principles are the basis for how police speed radar operates.

4. Which one of the following is NOT an electromagnetic wave ?

Which one of the following is NOT an electromagnetic wave ?

Light wave
Radio wave
Sound wave
Micro wave
This question was previously asked in
UPSC CAPF – 2019
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Sound waves are mechanical waves that require a medium (like air, water, or solids) to propagate. They are typically longitudinal waves in fluids.
– Electromagnetic waves are disturbances that can travel through a vacuum (like space) as well as through matter. They consist of oscillating electric and magnetic fields.
– Light waves, radio waves, and microwaves are all examples of electromagnetic waves, differing in their frequency and wavelength.
– The electromagnetic spectrum includes, in order of increasing frequency/energy and decreasing wavelength: Radio waves, Microwaves, Infrared radiation, Visible light, Ultraviolet radiation, X-rays, and Gamma rays.
– Sound waves are caused by vibrations that create pressure variations in the medium.

5. Which one of the following is NOT true for an electromagnetic wave ?

Which one of the following is NOT true for an electromagnetic wave ?

Electromagnetic wave transports energy and momentum
Electromagnetic wave can be polarized and reflected
Electromagnetic wave is longitudinal
Electromagnetic wave propagation is described by the varying electric and magnetic fields
This question was previously asked in
UPSC CAPF – 2019
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Electromagnetic waves are transverse waves, not longitudinal. In a transverse wave, the oscillations of the wave are perpendicular to the direction of wave propagation.
– Electromagnetic waves consist of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of propagation.
– They transport both energy and momentum.
– Being transverse waves, they can be polarized. They also undergo reflection, refraction, diffraction, and interference.
– Longitudinal waves, such as sound waves in air, involve oscillations parallel to the direction of propagation.
– The statement that electromagnetic wave propagation is described by varying electric and magnetic fields is fundamental to Maxwell’s equations, which govern their behaviour.

6. When a longitudinal wave moves through a certain medium, the quantity

When a longitudinal wave moves through a certain medium, the quantity which is transmitted through the medium is

material of the medium only
energy only
both material of the medium and energy
none of the above
This question was previously asked in
UPSC CAPF – 2019
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When a longitudinal wave moves through a medium, it is the energy that is transmitted through the medium, not the material itself. The particles of the medium oscillate about their equilibrium positions but do not travel long distances with the wave.
– A wave is a disturbance that transfers energy from one point to another.
– In a longitudinal wave, particles of the medium vibrate parallel to the direction of wave propagation.
– Examples of longitudinal waves include sound waves in air and pressure waves in fluids.
– This principle applies to both longitudinal and transverse mechanical waves; the medium oscillates but does not propagate. Electromagnetic waves also transmit energy and momentum through space without needing a physical medium, relying on oscillating fields.

7. Directions : The following eight (8) items consist of two statements,

Directions :
The following eight (8) items consist of two statements, Statement I and Statement II. Examine these two statements carefully and select the correct answer using the code given below.
Code :
Statement I : Sound waves can travel through vacuum.
Statement II : Light is an electromagnetic wave and can travel through vacuum.

Both the statements are individually true and Statement II is the correct explanation of Statement I
Both the statements are individually true but Statement II is not the correct explanation of Statement I
Statement I is true but Statement II is false
Statement I is false but Statement II is true
This question was previously asked in
UPSC CAPF – 2018
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The correct answer is D) Statement I is false but Statement II is true.
– Statement I: Sound waves are mechanical waves. They require a medium (solid, liquid, or gas) for propagation because they travel through the vibration of particles in the medium. Vacuum is devoid of such particles, hence sound cannot travel through vacuum. This statement is false.
– Statement II: Light waves are electromagnetic waves. Electromagnetic waves do not require a material medium for propagation; they can travel through vacuum. This is why light from the Sun reaches the Earth through the vacuum of space. This statement is true.
Electromagnetic waves travel at the speed of light ($c$) in vacuum. Sound waves travel at much slower speeds, which depend on the properties of the medium.

8. Which of the following statements is /are correct ? 1. Gravitationa

Which of the following statements is /are correct ?

  • 1. Gravitational Waves were predicted by Albert Einstein in 1916 on the basis of his theory of General Relativity
  • 2. Gravitational waves do also exist in the Newtonian theory of Gravitation
  • 3. Gravitational Waves are to be detected by very sensitive detectors known as Interferometers

Select the correct answer using the code given below :

1 only
1 and 3 only
2 and 3 only
1, 2 and 3
This question was previously asked in
UPSC CAPF – 2016
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Statements 1 and 3 are correct.
1. Albert Einstein predicted the existence of gravitational waves in 1916 as a consequence of his theory of General Relativity. This statement is correct.
2. The Newtonian theory of Gravitation describes gravity as an instantaneous force between masses. It does not predict the existence of gravitational waves which are ripples in spacetime propagating at the speed of light. This statement is incorrect.
3. Gravitational waves are extremely weak and require highly sensitive detectors. Interferometers, such as those used in the LIGO (Laser Interferometer Gravitational-Wave Observatory) and Virgo experiments, are the primary instruments used for their detection. This statement is correct.
The first direct detection of gravitational waves was made by the LIGO collaboration in September 2015 (and announced in February 2016), confirming Einstein’s prediction nearly a century later. This detection originated from the merger of two black holes.

9. A microwave oven uses wave with a

A microwave oven uses wave with a

large wavelength in the invisible range
small wavelength in the visible range
large wavelength in the visible range
small wavelength in the invisible range
This question was previously asked in
UPSC CAPF – 2012
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A microwave oven uses microwaves, which are electromagnetic waves. Microwaves have wavelengths that are longer than visible light, infrared, and ultraviolet radiation, but shorter than radio waves. They fall within the radio spectrum and are invisible to the human eye. Therefore, they have a small wavelength relative to radio waves but are definitely in the invisible range. Compared to visible light, their wavelength is larger, but option D specifies ‘small wavelength in the invisible range’, which is correct relative to, say, radio waves or considering the typical options comparing ‘visible’ vs ‘invisible’ and relative wavelength size.
– Microwaves are part of the electromagnetic spectrum.
– They are invisible to humans.
– The wavelengths are typically in the centimeter range.
Microwave ovens commonly operate at a frequency of 2.45 GHz, which corresponds to a wavelength of approximately 12.2 cm. This wavelength is efficient at heating water molecules in food.

10. A television remote uses

A television remote uses

infrared waves
cosmic waves
microwaves
ether waves
This question was previously asked in
UPSC CAPF – 2012
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Most traditional television remote controls use infrared (IR) light to send signals to the television. These signals are invisible to the human eye.
– Infrared waves are a type of electromagnetic radiation with wavelengths longer than visible light.
– IR communication is suitable for short-range, line-of-sight applications like remote controls.
Newer types of remote controls, particularly for smart TVs or other devices, may use radio waves (like Bluetooth or Wi-Fi) which do not require a direct line of sight. However, the vast majority of standard TV remotes use infrared.
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