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Nature and reflection of light
light. When light encounters a surface, it This ensures that the reflection is
predictably changes direction, following constrained to a two-dimensional
specific principles known as the laws of plane defined by the light ray and
reflection. These laws govern how light perpendicular to the surface at the
interacts with reflective surfaces, such point of incidence.
as mirrors (Figure 4.12) and determine
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the path of the reflected rays. They are Activity 4.4
essential for understanding the behaviour
of optical systems and have practical Aim: To investigate the laws of
applications in fields ranging from reflection
astronomy to everyday technologies
like periscopes, cameras, and fibre Materials: pins, soft board, plain paper,
optics. Activity 4.4 aids in experimental optical pins, mirror
exploration on laws governing reflection Procedure
of light. 1. Fix a plane paper on a soft board
using a pin, then draw a horizontal
Normal line
line across it.
Incident ray N Reflected ray 2. Align a mirror vertically on the line.
3. Place an optical pin in front of the
mirror so that you can see its image
in the mirror.
i 4. Line up the pin and its image and
r
place a second pin in front of the
R O Q mirror along the line of sight, as
shown in Figure 4.13.
Figure 4.12: Reflection of light from the
plane mirror Mirror
There are two laws of reflection that can
be stated as follows:
1. The angle of incidence is equal to
the angle of reflection. This means Line of sight Second pin
the angle at which the incoming light
ray strikes a surface (the angle of
incidence) is identical to the angle at
which it is reflected away (the angle
of reflection). Figure 4.13
2. The incident ray, the reflected ray,
and the normal to the reflective 5. Look at the image in the mirror from
surface all lie in the same plane. another direction and place two pins
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