Applied science Sem I UNIT 2

 UNIT 2: Optics

Electromagnetic wave nature of light

Light is a transverse electromagnetic wave. This means that light is a wave that is made up of electric and magnetic fields.

These fields are perpendicular to each other and to the direction of the wave's propagation

 

 

 

1. State law of reflection and Snell’s law of  refraction with diagram.

law of reflection: the incident ray, the reflected ray, and the normal to the surface of the mirror all lie in the same plane.
The angle of reflection is equal to the angle of incidence. 

Snell’s law:
1. The incident ray, the refracted ray, and the normal at the point of intersection, all lie in the same plane.
2. The ratio of the sine of the angle of incidence (i) to the sine of the angle of refraction (r) is equal to the refractive index of the medium, which is a constant.
sin i/sin r = μ

 

 

 

 

2. What is unpolarised light and plane polarised light?

Unpolarized light: Light in which vibrations of electric field are in all possible directions, which are perpendicular to the direction of propagation.

Polarized light : the light in which vibrations of electric field vectors are confined to one plane, and other vibrations are blocked.  

 

 

 

3. State law of Malus.

When a polarized light passes through another polarizer (analyser), making angle theta (θ) with the first polarizer, then the intensity of light becomes  I = I₀  cos²θ

**[ For any numerical related, write the above formula 

To get at least 1 mark]**

 

 

 

 

4. Explain refraction of light from denser to rarer medium. Hence explain total internal reflection.

Refraction: The phenomena of bending of a light ray when it travels from optically rarer medium optically denser medium , or vise-versa, is called refraction of light.

When a ray of light passedfrom a denser medium to a rare medium it bends away from the normal in the a rare medium.

Snell’s law for this case may be written as

sin θ2 = (μ1/μ2) sin θ1

Where θ1 is the angle of incidence of light ray in the denser medium and θ2 is the angle of

refraction in the rarer medium. Also μ1> μ2

 

• If θ1< θc, the ray refracts into the rarer medium.

• If θ1= θc, the light grazes the interface of rarer to denser medium

• If θ1> θc ,the ray is reflected back to the denser medium.

The phenomenon in which light is totally internally reflected from a denser to rarer medium boundary is called total internal reflection.

 

 

 

5. Define

(i) Plane of vibration:  The plane in which vibration of polarised light takes place is called plane of vibration.

(ii) plane of polarisation: The perpendicular plane to the plane of vibration in which there are no vibration is called plane of polarisation.