Determine and record the approximate focal length \(f_o\) of the concave mirror provided.
Arrange the ray box, the mirror, and the screen as shown in the diagram above.
Adjust the ray box to a distance b = 20.0cm from the mirror.
Adjust the position of the screen until a sharp image of the cross wire of the ray box is formed on it.
Measure and record the distance, a, of the screen from the mirror. Evaluate \(\frac{a}{a}\) =1.
Repeat the procedure for four other values of b = 25.0, 30.0, 35.0, and 40.0cm. Tabulate your readings.
Plot a graph of l on the vertical axis against a on the horizontal axis.
Determine the slope,.s, of the graph. Evaluate S\(^{-1}\).
State two precautions taken to ensure accurate results.
(b)i. An object is placed at a distance of 10cm in front of a concave mirror of focal length of 15cm. Determine the characteristics of the image formed.
ii. Briefly describe how you obtained \(f_o\) in (a)i) above.
Verified Correct Answer: .
Physical Principles & Numerical Solution
1. \(f_o\) = 15cm
5. a = 60.0cm, b = 20.0cm
Hence, L = \(\frac{a}{b} = \frac{60}{20}\) = 3
6. Tables of values/observation
S/N
b(cm)
a(cm)
L=\(\frac{a}{b}\)
1
20.0
60.00
3.00
2
25.0
37.00
1.50
3
30.0
30.00
1.00
4
35.0
26.00
0.75
5
40.0
24.00
0.6
7.
8. Slope (s) = \(\frac{\bigtriangleup {L }}{\bigtriangleup {a}} = \frac{3-0.25}{60-18.6cm}\)
= \(\frac{2.75}{41.4}\) = 0.066425cm\(^{-1}\)
S\(^{-1}\) = \(\frac{1}{s} = \frac{1}{0.066425(cm)^{-1}}\)
= 15.05 = 15
N.B: S\(^{-1}\) = \(f_o\) = 15cm
Precautions taken to ensure accurate results are as follows:
Parallax error in reading meter rule avoided
Readings repeated must De shown on the table
Collinear alignment of apparatus ensured
(b)i. u = 10cm, f = +15cm, V= ?
\(\frac{1}{v} + \frac{1}{u} = \frac{1}{f }\)
\(\frac{1}{v} + \frac{1}{10} = \frac{1}{15}\)
\(\frac{1}{v} = \frac{1}{15} - \frac{1}{10} = \frac{2-3}{30} =\frac{1}{30}\)
= The characteristics of the image formed are:
- it is virtual
- it is enlarged or magnified i.e twice or two times as big as the object (m = 2)
Source: Myschool Past Questions Archive (Record #60080)