Reflection - Physics | IBPS PO Prelims & Mains Preparation - Bank Exams PDF Download

Reflection

• The phenomenon due to which a beam of light, travelling through a certain medium, on striking some surface, bounce off from it in some other direction is called reflection of light.

Laws of reflection:

1. The incident ray, the reflection ray and the normal at the point of incident lie in the same plane.
2. Angle of incidence is always equal to angle of reflection.
3. When the two mirrors are placed at certain angle to each other then number of images formed will be,
                   n = (360 / Ø)-1 
4. The least size of the mirror required is half the height of the observer

Characteristics of image

• If the image is erect and of the same size as the object and it appears to be formed behind the mirror, the reflecting surface is plane.
• If the image is erect and formed behind the mirror but diminished in size for all positions of the mirror, the mirror must be convex.
• If the image is erect, formed behind the mirror and enlarged, then the mirror is concave.

Reflection in a concave & convex mirror

Reflection

Reflection of light on a concave mirror
Reflection of light on a convex mirror

Uses of concave mirrors

• Concave mirrors are commonly used in torches, search-lights and vehicles headlights to get powerful parallel beams of light.
• They are often used as shaving mirrors to see a larger image of the face.
• The dentists use concave mirrors to see large images of the teeth of patients.
• Large concave mirrors are used to concentrate sunlight to produce heat in solar furnaces.

Images by convex mirrors

 Refraction at a Plane Surface 

• When a ray of light passes from one medium to other it suffers a change in direction at the boundary of separation of two media.
• This phenomenon is called refraction.
• When a ray of light travels from one medium to another the wavelength and velocity of light change but the frequency does not change.

Refraction 

Refraction by Spherical Lenses

Refraction by Converging LensRefraction by Diverging Lens

 Image Formation by convex Lenses

Optical Instruments Physics

• Telescopes and microscopes are the aids to increase the apparent size of objects by increasing visual angle.
• Very distant objects (such as sun and moon), although very big in size appear very small because they subtend very small visual angle at the eye.
• To see them bigger, we cannot decrease their distance.
• But if with the help of proper lenses, a small image of the distant object be formed close to the eye then its image will subtend a large visual angle at the eye and the object will appear large. Telescope is based on this principle.
• Very small objects subtend small visual angle due to their smallness.
• We can increase the visual angle by bringing these objects closer to the eye, but we cannot do so beyond a certain limit (25cm) because then the objects will not be seen distinct.
• If with the help of proper lenses, a large image of small object is formed, then this image will subtend a large visual angle at the eye and the object will appear large. Microscope is based on this principle.