Important Study Notes on Reflection of Light

Study Notes on Reflection of Light

LIGHT

• Light is a form of energy, which is propagated as electromagnetic wave.
• It is the radiation which make our eyes able to ‘see the object. Its speed is 3 x 108 m/s. It is the form of energy. It is a transverse wave.
• It takes 8 min 19s to reach on the earth from the sun and the light reflected from moon takes 28s to reach earth.
• When light falls on the surface of an object it can either be

1. Absorbed – If an object absorbs all the light falling on it , then it will appear perfectly black for example a blackboard
2. Transmitted – An object is said to transmit light if it allows light to pass through itself and such objects are transparent.
3. Reflected – If an object sends back light rays falling on its surface then it is said to have reflected the light

Reflection of Light

• When a ray of light falls on a boundary separating two media comes back into the same media, then this phenomenon is called reflection of light.

Reflection from Plane Mirror

• If an object moves towards a plane mirror with speed v, relative to the object the moves towards it with a speed 2v.
• To see his full image in a plane mirror, a person required a mirror of at least half of his height.

Spherical Mirror

Spherical mirror are of two types

1. Concave mirror
2. Convex mirror

• Image formed by a convex mirror is always virtual, erect and diminished.
• Image formed by a concave mirror is generally real and inverted.

Uses of Concave Mirror

• As a shaving mirror
• As a reflector for the head lights of a vehicle, search light
• In ophthalmoscope to examine eye, ear, nose by doctors.
• In solar cookers.

Uses of Convex Mirror

• As a rear view mirror in vehicle because it provides the maximum rear field of view and image formed is always erect.
• In sodium reflector lamp.

Laws of Reflection of light

1. The angle of incidence is equal to the angle of reflection, and
2. The incident ray, the reflected ray and the normal to the mirror at the point of incidence all lie in the same plane.

NOTE: These laws of reflection are applicable to all types of reflecting surfaces including spherical surfaces

Refraction of Light

• The bending of the ray of light passing from one medium to other medium is called refraction. When a ray of light enters from one medium to other medium, its frequency and phase do not change, but wavelength and velocity change. Due to refraction form Earth’s atmosphere, the stars appear to twinkle.

Critical Angle

• The angle of incidence in a denser medium for which the angle of refraction in rarer medium becomes 90°, is called the critical angle.

Total Internal Reflection

• Sparkling of diamond, mirage and looming, shinning of air bubble in water and optical Fibre are examples of total internal reflection.