Light

We can see any object because light is reflected by that object and it reaches our eyes. But in the dark room, no light is reflected by the object so we are unable to see objects in dark room. If there is light present outside the room, then we can see the objects outside the room.

Diffused reflection is the result of irregularities in the surface from which reflection is occurring. It does not mean failure of laws of reflection.

(a) Regular reflection

A polished surface is an example of a smooth surface. A polished wooden table has a smooth surface. Hence, reflections from the polished table will be regular.

(b) Diffused reflection

Chalk power spread on a surface is an example of an irregular surface. It is not smooth.

Therefore, diffused reflection will take place from chalk powder.

(c) Diffused reflection

Cardboard surface is also an example of an irregular surface. Hence, diffused reflection will take place from a cardboard surface.

(d) Regular reflection

Marble floor with water spread over it is an example of a regular surface. This is because water makes the marble surface smooth. Hence, regular reflection will take place from this surface.

(e) Regular reflection

Mirror has a smooth surface. Therefore, it will give a regular reflection.

(f) Diffused reflection

Although a piece of paper may look smooth, but it has many irregularities on its surface. Due to this reason, it will give a diffused reflection.

The Laws of reflection are:

1) The angle of reflection is always equal to the angle of incidence.

2) The incident ray, the reflected ray and the normal to the reflective surface at the point of incidence all lie in the same plane.

AIM: To show that the incident ray, the reflected ray and the normal at the point of incidence lie in the same plane.

Material Required: Plane mirror, a sheet of paper, torch, pencil, meter scale.
Procedure:
1. Place a plane mirror on the table.
2. Take a sheet of paper and make a small hole in its centre.
3. Make sure that the light in the room is not bright.
4. Hold the sheet normal to the table.
5. Take another sheet and place it on the table in contact with the vertical mirror.
6. Draw a normal line on the second sheet from the mirror.
7. Now, light a torch on the mirror through the small hole such that the ray of light falls on the normal at the bottom of the mirror.
Diagram:


Observation:
When the ray from this hole is incident on the mirror, it gets reflected in a certain direction.
You can easily observe the incident ray, reflected ray and the normal to the mirror at the point of incidence on the sheet placed on the table.
Result:

This shows that the incident ray, the reflected ray, and the normal to the surface at the point of incidence all lie in the same plane.

(a) A person 1 m in front of a plane mirror seems to be 2 m away from his image.

(b) If you touch your left ear with your right hand in front of a plane mirror, it will be seen in the mirror that your right ear is touched with your left hand.

(c) The size of the pupil becomes large when you see in dim light.

(d) Night birds have less cones than rods in their eyes.

The correct answer is (a) Always

The angle of reflection is equal to angle of incidence always.

The correct option is (b) virtual, behind the mirror and of the same size as the object.

Plane mirror always form virtual image and of the same size and at the same distance from the mirror.

Three rectangular mirror strips of dimensions 15cm x 4cm (length is 15 cm and breadth is 4 cm) are joined together to form a prism as shown. This prism is fixed into a circular cardboard tube. The circular cardboard tube should be slightly longer that the prism. This circular tube is now closed at one end with a cardboard disc. This disc has a hole in it through which we can see. At the other end of the circular tube, a plane glass plate is fixed. It is important that this glass plate touches the prism mirrors. On this glass plate, several small and broken pieces of coloured glass are placed. This end is now closed by a round glass plate allowing enough space for the coloured glass pieces to move.

The labelled sketch of the human eye is shown below:

Laser light is harmful for the human eyes, because its intensity is very high and it carries lot f energy. It can cause damage to the retina and lead to blindness. Hence, it is advisable not to look at a laser beam directly.

Eyes are the most sensitive human organs. We can take care of eyes by:

1) Visiting an eye specialist regularly.

2) Avoid reading in dim light and very bright light.

3) Avoid direct exposure of sunlight to the eye. Use goggles to cover your eyes when stepping into sun.

4) Clean your eyes with cold water quickly if dust particles or small insects enter your eye.

5) Maintain a distance of at least 25 cm between the book and your eyes while reading.

From the laws of reflection,

The angle of incidence (∠i) = angle of reflection (∠r) Here as given ∠i + ∠r = 90°

∴ ∠i + ∠i = 90°
2∠i = 90
∠i = 90/2

∠i= 45 °

Hence angle of incidence of a ray = 45°

Infinite images of the candle will be formed due to parallel mirrors.

The first law of reflection is used to obtain the path of reflected light.

It can be observed that the given ray of light will reflect from the second mirror at an angle 60°.

Bojhoo is not standing in front of the mirror because the length of the mirror is too short on his side therefore, he cannot see his image in the mirror.

But, he can see the points P and Q, because light rays from P and Q get reflected from the mirror and are see by Boojho. Thus, he can see the images of point P and point Q.

Again, point R is not in front of the mirror. If the light rays from R get reflected by the mirror, then boojho can see point R as well.

(a) Image of the object placed at A is formed behind the mirror. The image is shown as A'.

Now, it is the characteristic of the image formation of plane mirror that "the distance of the image from the mirror is equal to the distance of the object from the mirror".

∴ The distance of A from the mirror is equal to the distance of A' from the mirror.

(b) Yes, Paheli at B position will be able to see this image. This is because of the reflected rays from the mirror will reach Paheli's eyes.

(c) Yes. Boojho at C can see this image. Because the position of Boojho is just ahead of Paheli, and not far away.

(d) Image of the object at A will not move. It will remain at the same position when Paheli moves from B to C.