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 Refractive Index n= Speed in Medium Speed in Vacuum ​

9. Lenses Convex Lens Converging lens

Uses:

Camera Microscope Magnifying glass Human eye correction (Hypermetropia) Concave Lens Diverging lens

Uses:

Spectacles for Myopia Door viewers Important Lens Terms Optical Centre (O) Principal Focus (F) Principal Axis Focal Length (f) Convex Lens Image Formation