Light – Reflection and Refraction

Notes

1. Light

Light is a form of energy that enables us to see objects.

Properties

Travels in a straight line.

Needs no material medium.

Speed in vacuum = 3 × 10⁸ m/s

2. Reflection of Light

Definition

The bouncing back of light into the same medium after striking a surface.

Laws of Reflection

Angle of incidence = Angle of reflection

∠i = ∠r

Incident ray, reflected ray and normal lie in one plane.

3. Spherical Mirrors

Types:

(A) Concave Mirror

Reflecting surface bends inward.

Converging mirror.

Uses:

Shaving mirror

Dentist's mirror

Headlights

Solar furnace

(B) Convex Mirror

Reflecting surface bends outward.

Diverging mirror.

Uses:

Rear-view mirrors

Security mirrors

4. Terms Related to Mirrors

Pole (P)

Centre of Curvature (C)

Radius of Curvature (R)

Principal Axis

Principal Focus (F)

Focal Length (f)

Relation

R = 2f

5. Ray Diagrams for Concave Mirror

Object at Infinity

Image:

At Focus (F)

Real

Inverted

Highly diminished

Beyond C

Image:

Between C and F

Real

Inverted

Smaller

At C

Image:

At C

Same size

Real

Inverted

Between C and F

Image:

Beyond C

Enlarged

Real

Inverted

At F

Image:

At Infinity

Between F and P

Image:

Behind mirror

Virtual

Erect

Enlarged

6. Convex Mirror Images

Always forms image:

Behind mirror

Between P and F

Virtual

Erect

Diminished

7. Sign Convention (New Cartesian)

Left side = Negative

Right side = Positive

Above Principal Axis = Positive

Below Principal Axis = Negative

Mirror Formula

f

1

​

=

v

1

​

+

u

1

​

Magnification

m=

h

o

​

h

i

​

​

=−

u

v

​

Where

hi = Image height

ho = Object height

u = Object distance

v = Image distance

8. Refraction

Definition:

Change in direction of light when it passes from one medium to another.

Cause:

Change in speed of light.

Laws of Refraction (Snell's Law)

Incident ray, refracted ray and normal lie in one plane.

sinr

sini

​

=Constant

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