Must Read: Light Wave

Light! Everybody knows what light means, but there are things about light that seem unknown to us. Light is a visible ray radiated from a source. The source may be sun, moon, star, torchlight, lamp etc.

However, the sources of light are known as luminous sources. Luminous source is a source of light that radiates light either naturally or artificially. Examples of luminous sources are sun, moon, stars, torchlight, candle, electric bulb etc.

Shadow was brought about due to the rectilinear propagation of light. Shadow is a region that light rays
do not reach due to the obstruction by an opaque object. Shadow consists of umbra and penumbra. Umbra is a region with the total darkness while, penumbra is the region with partial light rays. 

Light propagation rectilinear also causes a phenomenon known as eclipse. Eclipse occurs when the sun, the moon and the earth are collinear. When the moon is between the earth and the sun, solar eclipse ( eclipse of the sun ) is occurred. When the earth is between the sun and the moon, lunar eclipse ( eclipse of the moon ) takes place. Annular eclipse is formed when the moon's shadow is cast onto the earth's surface. Note, lunar eclipse occurs during the night while, solar eclipse occurs during the day.

Do you know the first camera on earth and when it was invented? The first camera is the pin hole camera, it was invented in 1550. It consists of a box at one end with a pin hole at the other end. When an object is placed in front of the pin hole, its image is inverted and seen on the screen. The closer the object to the pin hole, the larger and blurrier the image. While, the farther the object from the pin hole, the smaller and sharper the image. Note, the size of the image increases as the hole increases.

Let us consider what we call reflection on a plane surface. When a light ray travels and strikes a plane surface it can be absorbed, transmitted or reflected. Reflections are further classified into irregular reflections and regular reflections. Regular reflections are reflections that occur on a smooth surface, while irregular reflections are reflections  that occur on a rough surface. There are two laws of reflection which explain some terminologies about the incident ray and the reflected ray.

• First Law Of Reflection: This law states that the incident ray, the reflected ray and the normal all lie on the same common plane.
• Second Law Of Reflection: This law states that the angle of incidence is equal to the angle of reflection, provided the reflection on a smooth surface.

Types Of Images

There are two types of images - the real image and the virtual image

• Real images are images that light can pass through it. If a screen is placed at the position of the image, it can be seen.

• Virtual Images are images that light cannot pass through it but can be seen by the eye. Dear, the image formed on a plane mirror is a typical example of a virtual image.

The image characteristics of the image form on a plane mirror are as follows;

1. It has the same size as its object.
2. It is upright and erect.
3. It is a virtual image.
4. It is laterally inverted.

We all know that plane mirror is always used as a looking glass, especially during and after dressing. However, there are still some other uses of  plane mirror. Plane mirror is used in constructing sextant ( an instrument used in measuring the angle of elevation of the sun ). It is also used in constructing kaleidoscope ( common playing toy ) by inclining two plane mirror at 60^ to each other. Plane mirror is used essentially by the warrior because, it is used in constructing periscope ( instrument used in viewing  behind an obstacle at 45^ ).

A kaleidoscope

A sextant

There are still some mirrors classified as curve mirrors, they are the concave mirror and the convex mirror. In a concave mirror, ray of light converge while, in convex mirror rays of light diverge. Concave mirror with a large focal length is used as a shaving mirror. Convex mirror is used as a driving  mirror because it forms an erect image and gives a wide field of view. Parabolic concave mirror is used as a reflector of headlamps and for searchlight. Torchlight  uses concave reflecting surface to beam light.

RIGHT: Convex mirror; LEFT: Concave mirror