Page 147 - Physics_Form_2

Nature and reflection of light

Reflected
rays
Incident rays
Incident rays

FOR ONLINE READING ONLY
Principal axis Principal axis F C
C P P

Reflected rays Principal
f focus (F) f

Figure 4.21: Geometry of curved mirrors

The pole acts as the centre of the mirror, u is the distance from the object to the
with the principal focus (F) positioned pole. Magnification m is the ratio of the
halfway between the pole and the centre image height h to the object height h ,
i
0
of curvature (C). In concave mirrors, and it can also be expressed as the ratio of
the focal point is where all parallel the image distance to the object distance.
rays of light come together; in contrast, We perceive an image because light from
for convex mirrors, the focal point appears the object reflects off a mirror and travels
as a location from which light rays spread to our eyes, similar to how we see the
out. The radius of curvature (R) refers to object itself.
the radius of the sphere from which the
mirror originates, and the focal length (f) Relationship between focal length and

is half that radius, indicating the distance radius of curvature
from the mirror to the focal point. Figure Consider the reflection of light ray I from
4.21 shows the geometry of curved a concave mirror at point M. CM is a line
mirrors. normal to the mirror surface and passes
through the centre of curvature, and MF

A virtual image is formed when light rays is the reflected ray, which passes through
appear to originate but cannot be focused the focal point. Performing Activity 4.7
onto a screen, while a real image is created develops knowledge on practical solving
where actual light rays intersect and can for radius of curvature of curved mirrors.
be projected onto a screen. The image ∠i = ∠r (as we know that the angles of
distance v is the distance from the image incidence and reflection are equal)
point to the pole, and the object distance ∴ In ΔCMF, MF = CF

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Physics Form 2 Final.indd 141 25/10/2025 10:27