Muskan Shafi Education Content Expert
Education Content Expert
Speed of Light is the speed at which light passes on through any particular medium. Light has the fastest speed on Earth.
- The value of the speed of light varies from one medium to the other.
- It is denoted by the letter ‘c’.
- Speed of light in a vacuum is considered to be a fundamental constant in nature.
- Speed of light is 299,792,458 meters/second which is equivalent to approximately 3 × 108 m/s.
The equation of the speed of light can be expressed as:
c = ƒ X λ
Key Terms: Speed of Light, Reflection, Light, Vacuum, Refraction, Theory of Relativity, Laws of Reflection, Wavelength
What is Speed of Light?
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Speed of Light is defined as the speed at which light waves propagate through different materials.
- It is denoted by the letter c.
- It varies from one medium to another.
- The speed of light, when measured in a vacuum medium, is considered a fundamental constant.
- Light is considered to be the fastest-moving element on the Earth.
Speed of Light in Different Mediums
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Speed of light differs from one medium to the other. While in a vacuum medium, the speed of the light is constant, it is different while the light flows through air and water.
Speed of Light in Air
Speed of light through the air can be measured by the formula:
v = c/n
Where
- c = 3 × 108 m/s
- n = 1.0003 for Air
It is much less than the speed of light in a vacuum as it contains gases and other particles.
Speed of Light in Water
Speed of light is even slower in water than in vacuum and air as the water molecules are tightly bonded. Therefore, in this case, the speed of light is around 2.26×108 m/s.
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Equation of Speed of Light
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When light passes through any vacuum place, the speed of light is considered the fundamental constant. It is equal to the multiplication of its frequency and wavelength.
Therefore, the equation of the speed of light can be expressed as:
c = ƒ X λ
Where
- c = speed of light, (3.0 X 108 m/s in a vacuum)
- ƒ = frequency (Hz)
- λ= wavelength (m)
Reflection and Refraction
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Reflection of light is the bouncing back of light that strikes the medium on a plane, whereas, the core idea of Refraction is the process of the shift of light that passes through a medium leading to the bending of light.
Laws of Reflection
Here are the three important Laws of Reflection:
- First Law: “The angle between the incident ray and the normal is equal to the angle between the reflected ray and the normal.”
- Second Law: “The incident ray, the normal, and the reflected ray are all in the same plane.”
- Third Law: “Incident ray and refracted ray are on different sides of the normal.”
Laws of Refraction
Here are the three important Laws of Refraction-
- First Law: “The incident ray, the refracted ray, and the normal at the point of incidence, all lie in the same plane.”
- Second Law: “The ratio of the sine of the angle of incidence ‘i’ to the sine of the angle of refraction ‘r’ is constant for the pair of given media is always constant.”
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Things to Remember
- Speed of light is how quickly light travels through a given medium.
- Light has the highest speed on Earth.
- The Speed of Light differs in the case of vacuum, air, water, and other mediums.
- The speed of Light is considered to be a fundamental constant when it propagates through a vacuum.
- Speed of light is denoted as c = 299,792,458 meters/second.
- The equation of speed of light can be expressed as c = ƒ X λ.
Sample Questions
Ques. Define Speed of Light. (3 Marks)
Ans. Speed of Light can be easily defined as the speed at which light traveled through a particular medium. Therefore, it differs from one medium to the other. For example, the speed of light is much less in water than in a vacuum. The speed of light is 3 × 108 m/s. Light does not require a physical medium to travel, thus, it can also move through a vacuum.
Ques. What is Light? (2 Marks)
Ans. Light is defined as an electromagnetic radiation that allows the human eye to see objects. It is also referred to as visible radiation to the human eye. It always moves in a straight path or linear motion. It is a transverse wave that travels without a medium.
Ques. What are the factors that affect the speed of light? (3 Marks)
Ans. There are a few factors that affect the speed of light, such as
- The medium the light is passing through
- Properties of that medium
- The optical density of that medium
- Index of Refraction
Ques. Explain the Speed of Light in a vacuum. (2 Marks)
Ans. Light travels fastest when it travels through a vacuum place. It is then denoted as c, where c is equal to 299,792,458 meters/second to be exact. This is counted as a fundamental constant and helps us calculate other important equations like the Theory of Relativity.
Ques. What are the Laws of Reflection? (4 Marks)
Ans. There are three laws of reflection which are as follows:
- First Law of Reflection: “The angle between the incident ray and the normal is equal to the angle between the reflected ray and the normal.”
- Second Law of Reflection: “The incident ray, the normal, and the reflected ray are all in the same plane.”
- Third Law of Reflection: “Incident ray and refracted ray are on different sides of the normal.”
Ques. What is the equation of the speed of light? (3 Marks)
Ans. The rate of light varies from one medium to another. The equation of the speed of light can be expressed as
c = ƒ X λ
Where
- c is the speed of light (3.0 X 108 m/s in a vacuum).
- ƒ is the frequency (Hz).
- λ is the wavelength (m).
Ques. What is the speed of light through Air, Water, and Glass? (3 Marks)
Ans. The speed of light through Air, Water, and Glass is as follows:
- Speed of light in air is 3 × 108 m/s.
- Speed of light in water is 2.26×108 m/s.
- Speed of light in glass is 2 × 108 m/s.
Ques. The speed of light in a vacuum is 3 × 108 m/s and the speed of light in common glass is 2 × 108 m/s. Calculate the refractive index of glass. (3 Marks)
Ans. The Refractive Index of medium B concerning medium A is given as
Now, according to the question, the speed of light through a vacuum is 3 × 108 m/s and the speed of light glass is 2 × 108 m/s.
Hence, as per the equation, the refractive index of glass will be
Ques. Light is a form of _______ that can be detected with our ________. (1 mark)
a. energy, ears
b. corpuscles, eyes
c. energy, eyes
d. sensation, skin
Ans. c. energy, eyes
Explanation: Light, also referred to as visible light, is electromagnetic radiation that allows us to see objects around us. Also, the eyes are the sense organs that allow us to perceive things around us. Thus, light is a form of energy that can be detected with our eyes.
Ques. What is Light Energy? (2 Marks)
Ans. Light Energy is the energy produced by vibrations of electrically charged particles. Some examples of light energy are as follows:
- Energy used to cook food in a microwave oven is a form of light energy.
- Radar systems used for ATC (Air Traffic Control) use a form of light energy.
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