You have been provided with a rectangular glass prism, optical pins, and other necessary apparatus. Using the above diagram as a guide, carry out the following instructions:
Fix the drawing paper provided to the drawing board
Place the glass prism on the drawing paper and trace the outline, ABCD of the prism
Remove the prism, mark a point O on AB such that AO is about one-quarter of AB
Draw a normal through point O. Also draw an incident ray to make an angle i = 25 with the normal at O. Fix two pins at \(P_1\) and \(P_2\) On the incident ray.
Replace the prism. Fix two other pins at \(P_3\) and \(P_4\) such that the pins appear to be in a straight line with the images of the pins at \(P_1\) and \(P_2\) when viewed through the block along DC
remove the prism. Join points Pa and P4 and produce it to meet DC at 1. Also, draw a line to join Ol (
With O as center and using any Concinient radius, draw a circle to Cut the incident ray and the refracted ray at E and H respectively. Maintain this radius throughout the experiment
Draw the perpendiculars EF and GH. Measure and record d= EF and I= GH.
Repeat the procedure for four other values of i = 35^\circ, 45, 55^\circ, and 65^\circ respectively. In each case measure and record d and I
Plot a graph of d on the vertical axis against I on the horizontal axis
Determine the slope of the graph
State two precautions taken to ensure accurate results. [Attach your traces to your answer booklet)
(b)i. State Snell's law.
ii. Calculate the critical angle for a water-air interface. [refractive index of water = \(\frac{4}{3}\)]
Verified Correct Answer: .
Physical Principles & Numerical Solution
Table of values (Observation)
S/N
iº
d(cm)
i (cm)
1
25^\circ
0.85
0.55
2
35^\circ
1.15
0.75
3
45^\circ
1.50
0.95
4
55^\circ
1.65
1.10
5
65^\circ
1.85
1.20
Slope of the graph = \(\frac{y}{x} = \frac{\bigtriangleup {d}}{\bigtriangleup {L}} = \frac{1.4}{0.9}\) = 1.56
Precautions:
I ensured that pins were vertical.
l ensured that pins were reasonably spaced (at least 1 cm apart) and pinpoints were seen on traces.
I ensured neat traces (sharp pencils)
I noted and corrected zero errors on the metre rule.
l avoided parallax using metre rule/protractor
(b) Snell's law states that for a given pair of media, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is always a constant. Or The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant for the media concerned. Or
\(\frac{\text {sin i}}{\text {sin r}}\) = a constant for a given pair of media where
i = angle of incidence and
r = angle of refractions.
ii. \(\frac{1}{\text { sin C}}\) = \(_{a}\)\(n_w\)
Where C = critical angle, and
\(_{a}\)\(n_w\) = refractive index of water.
i.e. sin C = \(\frac{3}{4}\) = 0.75
C = sin\(^{-1}\), 0.75 = 48.6^\circ
Source: Myschool Past Questions Archive (Record #60068)