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Question

Which one of the following statements with regard to ultra violet light is NOT correct?

This question was previously asked in
CDS I 2020 Elementary Mathematics Previous Year Paper (02-Feb-2020)
The correct answer is

It is a longitudinal wave.

Understanding Ultra Violet Light Properties

Let's analyze the properties of ultra violet (UV) light and determine which of the given statements is NOT correct. Ultra violet light is a part of the electromagnetic spectrum, just like visible light, radio waves, X-rays, etc.

Properties of Electromagnetic Waves

Electromagnetic waves share several fundamental properties:

  • They are transverse waves, meaning the oscillations of the electric and magnetic fields are perpendicular to the direction the wave travels.
  • They can travel through a vacuum, like space. This is how light from the sun reaches Earth.
  • They travel at the speed of light in a vacuum, approximately \(3 \times 10^8\) meters per second.
  • They have a wide range of wavelengths and frequencies, which make up the electromagnetic spectrum.

Analyzing the Statements about Ultra Violet Light

Now let's look at each statement provided about ultra violet light:

  1. It is an electromagnetic wave. This statement is correct. Ultra violet light is indeed a segment of the electromagnetic spectrum.
  2. It can travel through vacuum. This statement is also correct. As an electromagnetic wave, UV light does not require a medium to travel and can pass through the vacuum of space, which is why we receive UV radiation from the sun.
  3. It is a longitudinal wave. This statement is NOT correct. Electromagnetic waves, including ultra violet light, are transverse waves, not longitudinal waves. In a longitudinal wave, like sound waves traveling through air, the oscillations are parallel to the direction of wave propagation.
  4. Its wavelength is shorter/ smaller than that of visible light. This statement is correct. The electromagnetic spectrum is ordered by wavelength and frequency. Ultra violet light is located next to the violet end of the visible light spectrum (hence "ultra" violet). UV light has higher frequency and shorter wavelengths compared to visible light.

Based on the analysis, the statement that is NOT correct with regard to ultra violet light is "It is a longitudinal wave."

Comparing Wave Types: Transverse vs. Longitudinal

Property Transverse Wave Longitudinal Wave
Oscillation Direction Perpendicular to wave direction Parallel to wave direction
Examples Light waves (including UV), waves on a string, water waves Sound waves, waves on a Slinky (compression/expansion)
Medium Required? Some (e.g., string, water); Electromagnetic waves (like UV) require NO medium (travel through vacuum) Yes (solid, liquid, or gas)

Since ultra violet light is an electromagnetic wave, it behaves as a transverse wave.

Revision Table: Ultra Violet Light Properties

Property Description Correct/Incorrect for UV?
Electromagnetic Wave Part of the spectrum (radio, micro, IR, visible, UV, X-ray, gamma) Correct
Travels through Vacuum Does not need a medium Correct
Wave Type Transverse vs. Longitudinal UV is Transverse (Statement says Longitudinal)
Wavelength vs. Visible Light Wavelength range compared to visible light (\(\sim 400-700\) nm) Shorter wavelength than visible light

Additional Information: The Electromagnetic Spectrum

The electromagnetic spectrum is the range of all types of electromagnetic radiation. Energy, wavelength, and frequency are related:

  • Higher frequency means shorter wavelength and higher energy.
  • Lower frequency means longer wavelength and lower energy.

The order of the spectrum from longest wavelength (lowest frequency/energy) to shortest wavelength (highest frequency/energy) is typically:

  • Radio waves
  • Microwaves
  • Infrared radiation (IR)
  • Visible light
  • Ultra violet radiation (UV)
  • X-rays
  • Gamma rays

Ultra violet light has wavelengths roughly between 10 nm and 400 nm, which is shorter than the wavelengths of visible light (about 400 nm to 700 nm).

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