Page 170 - Physics_Form_2

Physics for Secondary Schools

3. In a straight line, slowly move away from the bucket to a point where the coin is
just outside your line of view. That is, the coin is not visible. Mark this point as
M.
4. Pour gently clear water into the bucket and try to view the coin while standing at
point M.
5. Continue adding more water until the coin can be seen when viewed from point
FOR ONLINE READING ONLY
M as in Figure 5.1.

Water

Coin appears
here

Coin Coin

Empty container Container with water
Figure 5.1
Questions
(a) Explain why the coin can be seen when the water is added, but not before?
(b) Why does the coin become visible from point M after filling the bucket with water?
(c) Does the coin appear raised? Explain.
(d) Suggest other materials that can be used to demonstrate the refraction of light,
besides water used in this activity.

The coin appears raised due to the change of direction of rays of light at the boundary
between water and air, as shown in Figure 5.1.

Angle of incidence and angle of normal line. The ray of light in the first
refraction medium is called the incident ray and
When light passes from a medium such as the ray of light in the second medium
air to another medium such as glass, which is called the refracted ray. The angle
is optically denser than the first medium, between the incident ray and the normal
its velocity decreases. Conversely, when line is known as the angle of incidence
light passes from an optically denser and is denoted by the letter i. On the other
medium such as glass to a medium that hand, the angle between the refracted ray
is optically less dense like air, its velocity and the normal line is called the angle
of refraction, denoted by r. Figure 5.2,
increases. The line that is perpendicular shows the normal line, the incident ray,
to the boundary between the two media the refracted ray, the angle of incidence
through which light travels is called the
(i) and the angle of refraction (r).

164
Student’s Book Form Two

Physics Form 2 Final.indd 164 25/10/2025 10:27