Reflection of light : Light is wave and also a visible form of energy which is radiated outward from a source.
We are able to see object because of the light they produce reflects back to us or light that fall on them from other sources also reflects back to us
We have luminous and non luminous objects
luminous objects are those ones that produce their own light, examples are sun, stars, fireflies, glow worms, lamps, candle, electric light bulbs and many others
Non luminous objects (opaque): These are objects that do not produce their own light they are only seen when light from other sources fall on them and the reflection of light occur back into our eyes
Reflection of light by plane mirror
Reflection of light is a situation whereby light bounce back when it hits polished, smooth or shiny objects such as mirror, glass, water and metals.
The angle at which reflection of light occurs is the same angle at which the light hit the object
The light rays that hit the object is called incident rays while the one that reflected is called the reflected rays
We are able to see pictures of ourselves behind the mirror when we look through the mirror because of the reflection of light from our face.
Properties of image formed by plane mirror
- The size of the image is the same as the object
- The image is upright
- It is lateral inverted
- The is image is virtual, this mean that the image is not real and therefore it cannot be seen on the screen
The numbers of image formed inclined plane mirror
1.Two plane mirror that is inclined at 90oC produce three image of one object
- Two plane mirror parallel to each other produce infinite image of one object
The number of image formed by a plane mirror is given mathematically as
Where N= number of the image, and θ the angle at which the plane mirrors are inclined
Types of reflection of light
There are Two types of reflection of light
(I) regular reflection of light
(ii) scattered or diffused reflection of light
Regular reflection of light
Regular reflection of light occurs as incident ray hit a smooth object and parallel beam of light is reflected in one direction
Scattered or diffused reflection of light
Here the reflection of light is not parallel but a scattered or diffused one, this is because the incident ray hit a rough surface such as paper table and many others, and therefore, rays are reflected in different direction
Laws of reflection of light
1. The incident ray, reflected ray and the normal at the point of incidence all lies in the same plane
2. The angle of incidence is equal to angle of reflection
Application of reflection of light in a plane mirror
One of the applications of reflection of light is in construction of periscope. Two mirrors are used in construction of periscope that enables us to see over walls other obstacles. Periscopes also used in tank, to see out above the armour plating
In a simple periscope two parallel plane mirrors are fixed facing each other and inclined at angle 450 to the line joining them.
If a ray AO as shown above strike mirror m1 450 at A, is reflected downwards long AB and strike mirror m2 at 450 at B.
The ray is then reflected along BE. Hence the object hidden from view by the obstacle is thus brought to the eyes of the observer by the reflection of two mirrors.
Note that the periscope will not function properly if the mirrors are not adjusted so that the rays from the object meet both mirrors at 45o to the normal
Reflection of light by curved mirror
A curved surface can be produced by cutting out a part of spherical shell. If a light is reflected from the outside of this surface, a convex or a diverging mirror is produced If a light is reflected from the inside surface we have a concave or converging mirror.
Due to the curved nature of these mirrors they produce image in a way different from that of the plane mirrors
Concave mirrors are used in torches and car headlamp, in reflecting telescope and also as a shaving mirrors
Convex mirrors are often used as a driving mirrors and to see round corner in a supermarket
Curved mirror technology
1. The pole of the mirror: The pole of the mirror is the midpoint of the mirror
2. The centre of curvature: The centre of curvature is the centre of the sphere of which the mirror is apart
3. The principal axis: The principal axis is the line between pole and centre of curvature.
4. Radius of curvature: It is a distance between the centre of curvature and the pole
5. Principal focus: The principal focus of a concave mirror is the point where ray that are parallel and close to principal axis converge after reflection
6. Principal focus of convex mirror: It can be describe as a point where a ray parallel and close to principal axis diverge after reflection
Nature of image formed by concave mirror
The image formed by concave mirror depends on the position of objects in the front of mirror
1. When object is placed farther away from the mirror the image formed is real and smaller than the object and inverted
2. When the object is placed close to the mirror, the image size gets bigger, real and inverted
3. When object is placed at the centre of curvature of the mirror the image size become the same as the object, inverted and real.
4. When object is placed between the centre of curvature and principal focus, the image become larger than the object, real and inverted
5. when object is placed at the principal focus the image become virtual and can no longer form in screen
6. When object is placed between the principal focus and the pole, the image become larger erect and virtual
Nature of image formed by convex mirror
The image formed by convex mirror is always erect, smaller than the object and virtual.