
Using the above diagram as a guide, carry out the following experiment:
- place the equilateral triangular glass prism on the drawing paper. Trace the outline ABC of the prism.
- remove the prism. Draw a line NO such that it makes an angle i = 25ΒΊ with the normal at point O on side AB
- fix two pins R\(_{1}\) and R\(_{2}\) vertically on line N0. Replace the prism on its outline;
- place the reflecting surface of the plane mirror in contact with the face AC of the prism;
- looking through the face BC of the prism, fix two other pins at R\(_{3}\) and R\(_{4}\) such that the pins appear to be in a straight line with the images of the pins at R\(_{1}\) and R\(_{2}\);
- remove the prism, the mirror, and the pins. Draw a line to join points R\(_{4}\) and R\(_{3}\)
- produce line R\(_{4}\)R\(_{3}\) to meet line NO produced at T;
- measure and record the angle \(\theta\) at T and e at D;
- repeat the procedure for four other values of i = 30Β°, 35Β°, 40Β°, and 45Β°. In each case, measure and record the corresponding values of \(\theta\) and e. Tabulate your readings;
- plot a graph of e on the vertical axis and \(\theta\) on the horizontal axis;
- evaluate k = s\(^{-1}\)
- state two precautions taken to ensure accurate results. [Attach your traces to your answer booklet]
(b)i. State four characteristics of the image of an object formed by a plane mirror.
ii. State two Conditions necessary for total internal reflection to occur in a medium.
Explanation
Table of values (observation)
| S/N | iΒ° | \(\theta\)Β° | eΒΊ |
| 1 | 25 | 62 | 28 |
| 2 | 30 | 54 | 32 |
| 3 | 35 | 45 | 35 |
| 4 | 40 | 40 | 37 |
| 5 | 45 | 30 | 41 |
Slope (s) = \(\frac{\bigtriangleup {e}}{\bigtriangleup {\theta}}\) = \(\frac{49 - 20}{83 - 10} = \frac{29}{73}\) = 0.397
Intercept (c) = 53
Evaluation: K\(_{1}\) = S\(^{-1}\) = 0.397\(^{-1}\) = 2.519
Precautions;
- l ensured neat traces/sharp pencil (shown)
- I ensured mirror is firmly attached to prism
- I ensured pins are reasonably spaced (about 4 cm)
- l avoided parallax error in reading protractor.
(b)i. Characteristics of images formed by a plane mirror
- Same size as object
- Same distance from mirror as object
- Virtual
- Erect
- Laterally inverted.
ii. For total internal reflection of light to occur:
(a)Light must be travelling from a more dense to a less dense medium
(b)Angle of incidence in the denser medium must be greater than the critical angle