Trace the outline PQRS of the glass block on a sheet of paper, as shown in the diagram. Remove the block Mark a position 0 very close to P. Draw the normal NOG From point G, measure and mark out Points B\(_{1}\) B\(_{2}\) B\(_{3}\) B\(_{4}\) and B\(_{5}\) along with line GR at distances 1, 2, 3, 4 and 5cm respectively from G. Replace the glass block on the outline PORS Erect a pin at 0 and another at B\(_{1}\). Now fx a pin at T\(_{1}\) such that the pins at T\(_{1}\) and B\(_{1}\) are in line with the pin at O when viewed through the side SR of the glass block. Remove the glass block. Join the line OB\(_{1}\) and B\(_{1}\)T\(_{1}\). Measure and record the angles x and y. Evaluate sin x and y. Repeat the experiment with the pin at B\(_{1}\) fixed at B\(_{2}\), B\(_{3}\), B\(_{4}\) and B\(_{5}\) respectively while the pin at O remains unaltered. In each case, measure and record the values of x, y, sin x, and cos y. Tabulate your readings. Plot a graph of sin x on the vertical axis and cos y on the horizontal.axis, starting both axes from the origin (0,0). Calculate the slope, s of the graph. Evaluate K= \(\frac{1}{s}\). State two precautions taken to ensure accurate results. [Attach your tracings to your answer booklet]
(b)i. State Snell’s law of refraction and explain why reaction Occurs at the boundary between two media.
ii. Differentiate refraction from diffraction.
iii. State two conditions necessary for total internal reflection to occur in a medium.
Explanation
Table of values/observation
| S/N | X°(degree) | y° (degree) | Sin x | Cos y |
| 1 | 10.00 | 74.00 | 0.1736 | 0.2756 |
| 2 | 20.00 | 61.50 | 0.3420 | 0.4772 |
| 3 | 27.50 | 47.00 | 0.4617 | 0.6820 |
| 4 | 34.00 | 33.5 | 0.5592 | 0.8339 |
| 5 | 40.00 | 26.00 | 0.6428 | 0.8988 |
| 6 | 44.00 | 14.00 | 0.6947 | 0.9703 |
Slope (s) = \(\frac{\bigtriangleup {\text {sin x}}}{\bigtriangleup {\text {cos y}}} = \frac{0.69-0.03}{0.97-0.1}\)
= \(\frac{0.66}{0.87}\) = 0.7586 = 0.76
K = \(\frac{1}{S} = \frac{1}{0.7586}\) = 1.318 \(\approx\) 1.32
Precautions:
- I ensured that the optical pins were vertical
- l ensured reasonable spacing of pins.
- I used a sharp pencil.
- l avoided parallax error in reading the protractor.
(b)i. \(\frac{\text {sin i}}{\text {sin r}}\) = constant for a given pair of media where
i = angle sin r of incidence and
r = angle of retraction.
(ii) Retraction is the bending of rays at the interface of two media while diffraction is the spreading out of rays of light around the edges of obstacles or aperture.
(iii)(1) Light must travel from a dense medium to a less dense medium.
(2) The angle of incidence in the dense medium must be greater than the critical angle.