Refraction of light

REFRACTION

There is a change in the direction and speed of a ray of light when it passes from medium to another medium of different density.  This change in the direction of the light of the light ray which is due to difference in the speed of light in different media is called refraction.

When a ray of light travels from optically less dense medium (air) to an optically dense medium (water, glass), it bends towards the normal.

A ray passing from glass or water to air is bent away from the normal

When a wave, e.g light wave is refracted,

1. Its direction of travel changes
2. Its velocity changes.
3. Its wavelength changes
4. Its frequency remains the same.

REFRACTION THROUGH RECTANGULAR PRISM

LAWS OF REFRACTION

1.          The incident and refracted ray are in opposite sides of the normal at the point of incidence, all the three are in the same plane.

2.         The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant for a given pair of media.

The second law is known as Snell’s law

EFFECTS OF REFRACTION

The phenomenon of refraction is responsible for the following

1 The bottom of a clear river or pond appears shallower than it really is

2 A rod or spoon appears bent or broken when it is partially immersed in water or any liquid

3 Letters in print seem to be nearer when we place a thick block of glass over them.     

General Revision

1. The magnitude of the resultant of two mutually perpendicular forces F₁ and F₂ is 13N. If the magnitude of F₁ is 5N what is the magnitude of F₂? (a)16.0N  (b) 12.0N

2. Two 10N forces are inclined at an angle of 30⁰ to each other the magnitude of the resultant force is?

Reading Assignment: New School Physics Pages 290 – 292 

WEEKEND ASSIGNMENT

1 The direction of a light ray changes as it passes from one medium to another. This     phenomenon is called A diffraction B reflection C dispersion D refraction

2   The velocities of light in air and glass are 3.0 x10⁸ m/s and 1.8 x10⁸ m/s respectively. Calculate     the sine of the angle of incidence that will produce an angle of refraction of 30⁰ for a ray of     light incident on glass A. 1.2             B.  1.0   C . 0.8   D.  0.6

3   A transparent rectangular block 5.0 cm thick is placed on a black dot. The dot when viewed      from above is seen 3.0 cm from the top of the block. Calculate the refractive index of the     material of the block A.  2/5             B.  3/5 C. 3/2   D. 5/3 E.  5/2

4   When a ray of sunlight passes obliquely through a rectangular glass block

     A.  it emerges without displacement parallel to the incident ray

     B. it gets dispersed into seven visible colours without any deviation at all

     C. it deviates without dispersion

     D. it gets laterally displaced and the emergent ray is parallel to the incident ray

5   The absolute refractive indexes of glass and water are 3/2 and 4/3 respectively. The       refractive at the interface when a ray travels from water to glass is A ½ B 8/9 C 9/8 D17/12

THEORY

1 A ray of light passes from air  through a rectangular block of glass with parallel side 4.5 cm apart at an angle of incidence of 52⁰,find

(a) The lateral displacement of the ray (b) The angle of refraction (Refractive index of glass=1.5)

2  Radio wave travels on air at 3.0X10⁸m/s. if the waves enter water of refractive index of 4/3 , calculate the speed of the radio waves in water.