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# Light

## 01 Introduction to Light

#### 1. RAY OPTICS

Light may be of many forms: UV lights, infrared lights, colourful lights. Ray Optics deals with visible light whose wavelength lies between 400nm to 750nm and frequency lies between 400THz to 800 THz.. Light travels at 3*10^8 m/s in vacuum

#### 2. LIGHT

It is a form of electromagnetic radiation (radiant energy) which makes objects visible. When the light ray falls on an object, it is reflected back and enters our eyes. This produces sensation of vision.

#### 3. ELECTROMAGNETIC WAVES

It is a wave constituted by oscillating electric and magnetic fields which oscillate in mutually perpendicular directions and also perpendicular to the direction of propagation of the wave.

Properties of electromagnetic waves:

(i) They are transverse in nature.
(ii) They do not require any medium for their propagation.
(iii) They travel through vacuum with an enormous speed of 3 108 m/s.
(iv) The speed of an electromagnetic wave depends on the nature of the medium.

#### 4. NATURE AND THEORIES OF LIGHT

• Light waves travel in straight lines.
• There are two theories about the nature of light, namely:

(i) Wave theory of light
(ii) Particle theory of light

(i)WAVE THEORY OF LIGHT

According to wave theory, light consists of electromagnetic waves which do not require a material medium (like solid, liquid or gas) for their propagation.

(ii)PARTICLE THEORY

According to particle theory, light is composed of particles which travel in a straight line at very high speed.

#### Lens Formula, Magnification and Power of Lens

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