Physics
WAEC 2003
Using the diagram above as a guide, carry out the following instructions:
- Fix. the drawing paper provided on the drawing board
- Place the mirror vertically with its longer side resting on the drawing paper. Trace the outline AB of the mirror. Remove the mirror.
- Draw a normal PQ to meet the outline at the middle Q.
- Draw a straight line through A to meet the outline of the mirror at the right angle.
- Trace the incident ray, Q with pins P\(_{1}\) and P\(_{2}\) so that it meets the perpendicular line through A at C such that CA=X= 1.0m.
- Replace the mirror on its outline. Locate the images of P\(_{1}\)P\(_{2}\) through the mirror using two other pins P\(_{3}\) and P\(_{4}\) so that P\(_{3}\) and P\(_{4}\) and the images of P\(_{1}\) and P\(_{2}\) are in a straight line.
- Remove the mirror and pins P\(_{3}\) and P\(_{4}\).
Draw a straight line through the pin points to meet AB at Q and CA produced at D.
- Measure and record angle ACQ as è\(_{1}\), and angle ADCQ as è\(_{2}\). Also, record the value of x. Evaluate è = (è\(_{1}\) + è\(_{2}\)), x\(^{-1}\) and tan è.
- Repeat the procedure for four other values of x = 2.0, 3.0, 4.0 and 5.0cm. Tabulate your readings.
- Plot a graph of tan è on the vertical axis against x on the horizontal axis.
- Determine the slope, s, of the graph. Evaluate k = 2s
- State two precautions taken to ensure accurate results. Attach your traces to your answer booklet.
(b)i. Distinguish between regular and diffused reflections.
ii. An object is situated 25cm in front of a plane mirror. Determine the distance of the image from the object. What is the size of the image relative to the object?
Explanation
Table of values / observations
| S/N |
\(\theta_{1}^{o}\) |
\(\theta_{2}^{o}\) |
x(cm) |
x\(^{-1}\)(cm\(^{-1}\)) |
\(\theta\)=½(\(\theta_{1}\) + \(\theta_{2}\)) |
tan\(\theta\) |
| 1 |
83.0 |
81.0 |
1.0 |
1.00 |
82.0 |
7.115 |
| 2 |
76.0 |
74.0 |
2.0 |
0.50 |
75.0 |
3.732 |
| 3 |
69.0 |
70.0 |
3.0 |
0.33 |
69.5 |
2.675 |
| 4 |
62.0 |
63.0 |
4.0 |
0.25 |
62.5 |
1.921 |
| 5 |
57.0 |
58.0 |
5.0 |
0.20 |
57.5 |
1.570 |
Slope (s) = \(\frac{\bigtriangleup {tan \theta}}{\bigtriangleup {x}^{-1}} = \frac{7.2-1.2}{1-0.14} = \frac{6}{0.86}\) = 6.977 \(\approx\) 6.98
K = 25 = 2x 6.977 = 13.954, \(\approx\) 14
Precautions: i
- The optical pins must be straight and not bent. i.e pins are vertical
- Avoid error due to parallax
- Ensure reasonable spacing of pins
- Ensure that the object pins and the image pins are in a straight line.
- Ensure the Use of a sharp-pointed pencil so as to obtain neat traces and accurate angular measurement.
(b)i. Regular reflection occurs on a smooth surface giving rise to uniform (same) turning back of light rays when they fall on a surface. Diffused reflection occurs on a rough surface giving rise to a non-uniform (different) turning back to light rays when they fall on a surface.
ii.
Distance of the image from the object = 25-(-25)
= 25 + 25 =50cm
The size of the image is the same as the object.
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