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Notes, Exercises, Videos, Tests and Things to Remember on Light

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## Note on Light

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Light is a form of energy which produces the sensation of sight. The main source of heat and light energy in the earth is the sun.

#### Refraction of light

The bending of light as it passes from one medium to another medium is called refraction of light.

Laws of refraction of light

• The incident ray, the refracted ray and the normal at the point of incidence all lie in the same plane. In the figure, the incident ray AO refracted ray OB and normal ray MN at the point of incidence O; all lie in the same plane.

• The ratio of the sine of the angle of refraction is constant for a given pair of media. This is also called Snell’s law.

Mathematically, i.e = (µ) constant.

In the figure,∠ i is the angle of incidence in the air and ∠ r is the angle of refraction. In another medium glass in which the light enters. The ‘constant’ is called refractive index (R.I.) of the glass where light enters. It is denoted by µ. The Snell’s law can be stated in the following ways:

• When a light rays travel from rarer to a denser medium, it bends towards the normal. It means the angle of incidence is greater than the angle of refraction.
• When the light passes from a denser to a rarer medium, it bends away from the normal. It means the angle of incidence (∠i) is smaller than the angle of refraction (∠r).
• When the light passes along the normal i.e. at a right angle to the surface, it passes without deviation.

• Light is a form of energy which produces the sensation of sight.
• The main source of heat and light energy in the earth is sun.
• The bending of light as it passes from one medium to another medium is called refraction of light
• When a light rays travels from rarer to a denser medium, it bends towards the normal.
• When the light passes along the normal i.e. at right angle to the surface, it passes without deviation
.

### Very Short Questions

A light is a form of energy. A beam of light always travels in a straight line but when it passes from one medium to another, it gets bent.

The mediums of light are as follows:

1. Rarer medium: The medium with less density in comparison to other medium is called rarer medium.
2. Denser medium: The medium with greater density compared to other medium is called denser medium.
Eg: For air and water, air is rarer and water is denser
For water and glass, water is rarer and glass is denser.

The process of bending of light as it passes from one medium to another medium is called refraction of light.

The velocity of light in rarer medium is higher than the denser medium. Because of variation in speed of light at two media, it bends. So the change in speed of light when it passes from one medium to another medium is the main cause of refraction.

The effects of refraction are as follows: (i) A stick partly immersed in water and placed inclined to the surface, appears bent at the surface. (ii) A swimming pool appears swallower than it really is.

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• ### What is false about light?

light can pass through vaccum
light is stored in plant cell by photosynthesis
light is a electro-mechanical wave
very hot bodies can also be source of light

Diamond
Alcohol
Glass
benzene

heat

electricity

sound

light

• ### The bending of light as it passes from one medium to another medium is called ______.

defracton of light

deflection of light

refraction of light

reflection of light

• ### When a light rays travels from rarer to a denser medium, it bends towards the normal. It means the angle of incidence is ______.

greater than the angle of reflection

smaller than the angle of refraction

greater than the angle of refraction

smaller than the angle of reflection

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