What is Refraction?The phenomenon in which

there is a change in the speed of light as it travels from one medium to another and consequent bending of a ray of light incident obliquely at the surface of separation of the 2 media is known as refraction of light.If you observe a pencil in a glass of water, it will appear to be bent or displaced due to the effect of refraction.

Effect of Refraction

Snell’s Law

• Snell’s law states that for a given pair of media and for light of a given wavelength, ratio of the sine of the angle of incidence and the sine of the angle of refraction is a constant. This constant is called the refractive index of the second medium with respect to the first.

Where is the refractive index of the second medium with respect to the first.i is the angle of incidence and r is the angle of refraction.

r

in

sin

sin21

21n

What is Lateral Shift?When a ray of light from a

medium is incident on another medium with different optical density, the ray bends due to refraction. The perpendicular distance between the emergent ray and the incident ray is called the lateral shift. The angle which the incident ray makes with the normal is called angle of incidence denoted by 'i' and the angle made by the refracted ray with the normal is called the angle of refraction denoted by 'r'.

In the figure,ABCD is a glass slab.IO is the incident ray and O'E is the

emergent ray. O‘X is the lateral shift

Lateral Shift

Lateral shift is given by the formula:-

)sin(seccos

)sin(rirt

r

ritLs

Where t is the thickness of the glass slab, i is the angle of incidence and r is the angle of refraction

Factors affecting Lateral Shift

Lateral shift depends upon:-

Thickness of the slab

Refractive index of the material of the glass slab.

Angle of incidence

Wavelength of incident light

Experiment to determine Lateral Shift

• Aim: To find the lateral shift at different angles and to verify Snell’s Law.

• Apparatus: Glass slab and pins

• Procedure:-

o Outline the glass slab on a sheet of paper and draw a normal to 1 side of the slab.

o Place 2 pins one behind the other and view the pins from the other side. Mark the points where the pins seem to coincide, join them and extend the line.

o Measure the angle of incidence, angle of refraction and calculate the lateral shift by using the formula.

o Verify Snell’s law by substituting the values in the formula.

o Repeat the experiment with different angles of incidence.

Result

SL No. Angle of incidence ‘i’

Angle of refraction ‘r’

Lateral Shift (m)

Refractive index ‘n’

Trial No 1 45 25 2.2 x 10-2 1.67

Trial No 2 60 33 3.24 x 10-2 1.59

Trial No 3 85 39 5.55 x 10-2 1.58