Page 162 - Physics_Form_2

Physics for Secondary Schools

8. Measure the image distance, v, from Procedure
the screen to the mirror and the object 1. Mount the concave mirror on a
distance, u, from the crosswire to the bench.
mirror
9. Change the object distance and 2. Fix an optical pin on a cork, then fix
measure the corresponding image it on a screen.
FOR ONLINE READING ONLY
distances. Obtain at least 5 sets of u 3. Move the pin (object) until an
and v. inverted (real) image appears in
10. Using the mirror equation, front of the mirror, as illustrated in
1 1 1 Figure 4.32.
= + :
f u v
(a) Calculate the focal length of the
mirror

(b) Determine the average focal Image
length of the mirror. Screen

Question

Why did you obtain different values Metre rule
of f for different sets of u and v? Object

This activity has shown that the unknown Figure 4.32
focal length of a concave mirror can be
determined by experimenting with an 4. Adjust the position of the object pin
illuminated object. Although measurement until there is no parallax between it
errors can affect the experiment, the method and its image.
can effectively estimate the focal length of a 5. Measure the distance between the
given concave mirror. mirror and the image formed at this
point.
Activity 4.12

Questions
Aim: To determine the focal What is the significance of the distance
length of a concave mirror between the mirror and its image?
using a non-parallax
method. From this activity, the position of the image

Materials: concave mirror, bench, pin is at the centre of curvature. The focal
optical pins, screen, metre length of the mirror can be obtained from;
rule, corks f = R
2 .

156
Student’s Book Form Two

Physics Form 2 Final.indd 156 25/10/2025 10:27