The form of electromagnetic radio waves such as X-rays, microwaves, infrared radiation, and ultraviolet radiation are known as visible light waves. For instance, the colours of a rainbow can be considered as a band of these waves where each colour has a different wavelength. Violet has the shortest wavelength, and red has the longest wavelength. All the waves form white light when seen or merged together. When white light is passed through a prism, it gets dispersed into the seven colours of the visible light spectrum.
At different frequencies and wavelengths, electromagnetic radiation can be transmitted in waves or particles. This extensive variety of wavelengths is known as the electromagnetic spectrum, which is divided into seven areas in increasing order of energy and decreasing order of wavelength.
What is the visible light spectrum?
The visible light spectrum is the part of the electromagnetic spectrum that is visible to the human eye. The visible light spectrum is a scale that divides the light into different types of wavelengths, from low wavelength to high wavelength. Colour is the most important characteristic of visible light, which is both a characteristic property of light and an object of the human eye.
Important Questions on Visible Light
1) Which among the following rays has the maximum frequency?
a) Visible Rays
b) Gamma Rays
c) UV
d) Radio Waves
Correct Option: (b)
Explanation: When the electromagnetic spectrum is arranged in the decreasing order of frequency, gamma rays come first; hence it has the maximum frequency.
2) Which among the following colours has the maximum wavelength in the visible spectrum?
a) Blue
b) Violet
c) Red
d) Yellow
Correct Option: (c)
Explanation: In the electromagnetic spectrum, the colour red lies towards the right when arranged in the increasing order of wavelength. Therefore, red has the maximum wavelength in the visible spectrum.
3) The relation between wavelength and frequency can be given as _____.
a) Speed of light = wavelength / frequency
b) Frequency = wavelength / speed of light
c) Wavelength = speed of light / frequency
d) Speed of light = wavelength x frequency
Correct Option: (c)
Explanation: The relation between wavelength and frequency can be given as wavelength = speed of light (c) / frequency.
4) In the absence of the atmosphere, the colour of the sky will be _____.
a) Red
b) Dark
c) Yellow
d) Blue
Correct Option: (b)
Explanation: In the absence of the atmosphere, there will be no scattering of sunlight. This is the reason why the sky will appear dark and no longer be blue in the absence of an atmosphere.
5) _____ is the main principle used in interference.
a) Huygens’s principle
b) Principle of superposition
c) Quantum theory
d) Heisenberg’s uncertainty principle
Correct Option: (b)
Explanation: The elementary or fundamental principle used in the interference of light is the principle of superposition. The intensity increases when the incoming light waves superimpose positively, and on the other hand, when they add destructively, the intensity decreases.
6) Name the scientist who proposed the quantum theory of light.
a) Albert Einstein
b) Isaac Newton
c) Michel Faraday
d) Max Planck
Correct Option: (d)
Explanation: The quantum theory of light was proposed by Max Planck, which states that light contains minor particles in the form of isolated bundles of energy which are called photons.
7) The light in the Huygens’s wave theory was considered to be _____.
a) Transverse waves
b) Longitudinal waves
c) Of dual nature
d) None of these
Correct Option: (b)
Explanation: Huygens’s wave theory which explained reflection, refraction, diffraction, and interference, considered the light to be a periodic disturbance that is transmitted in the form of longitudinal waves through a medium.
8) Which among the following is an achromatic light?
a) Visible light
b) Monochromatic light
c) Chromatic light
d) Infrared light
Correct Option: (b)
Explanation: Monochromatic light, that is, the light void of colour, is also known as achromatic light.
9) The classification of electromagnetic waves is done on the basis of _____.
a) Electromagnetic spectrum
b) Propagation constant
c) Magnetic field
d) None of these
Correct Option: (a)
Explanation: The classification of electromagnetic waves is done on the basis of the electromagnetic spectrum. Since the wavelength or frequency determines the basic difference between various types of electromagnetic waves and also the waves propagate through the vacuum at the same speed, the waves vary in their mode of interaction with matter.
10) Which among the following is the reason for the blue colour of the ocean?
a) Total internal reflection
b) Scattering of light by water molecules
c) Polarisation
d) Interference
Correct Option: (b)
Explanation: The preferential scattering of light by water molecules is the reason behind the blue colour of oceans. This is the fundamental reason for several other phenomena, such as the reddish or blue sky at the time of sunrise or sunset.
Practice Questions
1) What is refraction?
2) Define total internal reflection.
3) What is the electromagnetic spectrum?
4) What is polarisation?
5) What do you mean by scattering of light?
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