class 10 experiment science
Aim
To trace the path of the rays of light through a glass prism.
Theory
What is a prism?
A prism is defined as a polyhedron with a triangular base and three triangular lateral surfaces. It is used as an optical object to study the behaviour of white light when it is passed through it. The light bends at various angles like an angle of incidence, angle of reflection, angle of refraction, and angle of deviation.
What is angle of deviation?
The angle of deviation is defined as the angle between the incident ray and the emerging ray. It is defined for the triangular prism.
Materials Required
Following are the list of materials required for this experiment:
A white sheet
Soft board
Thumb pins
4-6 all pins
Prism
Pencil
Scale
Protractor
Drawing board
Experimental Setup
Procedure
1)Fix a white sheet on a drawing board using drawing pins.
2)Place the triangular prism resting on its triangular base. Using a pencil, draw the outline of the prism.
3)Draw NEN normal to the face of the prism AB. make an angle between 30° and 60°.
On the line PE, fix two pins at a distance of 5cm from each other and mark these as P and Q.
4)Look for the images of the pins at P and Q through the other face of the prism AC.
Fix two pins at R and S such that they appear as a straight line as that of the P and Q when it is viewed from AC face of the prism.
5)Remove the pins and the prism.
At point F, make the points R and S meet by extending them.
6)PQE is the incident ray which is extended till it meets face AC. SRF is the emergent ray which is extended backward to meet at point G.
7)Now mark the angle of incidence ∠i, angle of refraction ∠r and the angle of emergence ∠e and ∠D as shown in the experimental setup.
8)Repeat the experiment for more angles between 30° and 60°.
Observations
1) At surface AB, the light ray enters and bends towards the normal on refraction.
At surface AC, the light ray bends away from the normal as it travels from one medium (glass) to the other (air).
2)The angle of deviation is observed. Here, the emergent ray bends at an angle towards the direction of the incident ray
Conclusion
1)The incident ray bends towards the normal when it enters the prism and while leaving the prism it bends away from the normal.
2)With the increase in the angle of incidence, the angle of deviation decreases. After attaining the minimum value, it increases with an increase in the angle of incidence.
Precautions
For drawing the boundary of the prism, a sharp pencil should be used.
Soft board and pointed pins should be used.
The distance between the pins should be 5cm or more.
The pins should be fixed vertically and should be encircled when they are removed from the board.
The angle of incidence should be between 30° and 60°.
The arrows drawn for incident ray, reflected ray and emergent ray should be proper.
For viewing the col-linearity of all the four pins and images, the head should be slightly tilted on either side. While doing this it can appear as all are moving together.