Reflection Of Light

REFLECTION OF  LIGHT

One way to change the direction of light is to let it fall on a shiny surface. For example, a shining stainless steel plate or a shining steel spoon can change the direction of light. The surface of water can also act like a mirror and change the path of light. Have you ever seen the reflection of trees or buildings in water (Fig. 15.3)

Any polished or a shiny surface can act as a mirror. What happens when light falls on a mirror?

You have learnt in Class VI that a mirror changes the direction of light that falls on it. This change of direction by a mirror is called reflection of light.

Reflection Of Light

REFLECTION OF  LIGHT

One way to change the direction of light is to let it fall on a shiny surface. For example, a shining stainless steel plate or a shining steel spoon can change the direction of light. The surface of water can also act like a mirror and change the path of light. Have you ever seen the reflection of trees or buildings in water (Fig. 15.3)

Any polished or a shiny surface can act as a mirror. What happens when light falls on a mirror?

You have learnt in Class VI that a mirror changes the direction of light that falls on it. This change of direction by a mirror is called reflection of light.

Reflection Of Light From A Mirror

Can you recall the activity in which you got the light of a torch reflected from a mirror? Let us perform a similar activity.

Activity 15.1

Take a torch. Cover its glass with a chart paper which has three narrow slits as shown in Fig. 15.5. Spread a sheet of 

chart paper on a smooth wooden board. Fix a plane mirror strip vertically on the chart paper (Fig. 15.5). Now direct the beam of light on the mirror from the torch with slits. Place the torch in such a way that its light is seen along the chart paper on the board. Now adjust its position so that the light from the torch strikes the plane mirror at an angle (Fig. 15.5).

Does the mirror change the direction of light that falls on it? Now move the torch slightly to either side. Do you find any change in the direction of reflected light?

Look into the mirror along the direction of the reflected light. Do you see the slits in the mirror? This is the image of the slits.

This activity shows how light gets reflected from a plane mirror.

Let us play around with the images formed in mirrors and know a little more about them 

Image Of Candle In A Plane Mirror

Activity 15.2

Place a lighted candle in front of a plane mirror. Try to see the flame of the candle in the mirror. It appears as if a similar candle is placed behind the mirror. The candle, which appears behind the mirror, is the image of the candle formed by the mirror (Fig. 15.6). The candle itself is the object.

Now move the candle to different positions in front of the mirror. Observe the image in each case.

Was the image upright in each case? Did the flame appear on top of the candle as in the object? Such an image is called erect. An image formed by a plane mirror is erect and of the same size as the object.

Now place a vertical screen behind the mirror. Try to obtain the image of the candle on this screen. Can you get the image on the screen? Now place the screen in front of the mirror. Can you get the image on the screen now? You will find that the image of the candle cannot be obtained on the screen in either case.

Locating Image In A Plane Mirror

What about the distance of the image from mirror? Let us perform another activity

Activity 15.3

Take a chess board. If a chess board is not available, draw on a chart paper 64 (8×8) squares of equal size. Draw a thick line in the middle of the paper. Fix a plane mirror vertically on this line. Place any small object, such as a pencil sharpner, at the boundary of the third square counting from the mirror (Fig. 15.7). Note the position of the image. Now shift the object to the boundary of the fourth square. Again note the position of the image.Did you find any relation between the distance of the image from the mirror and that of the object in front of it?

You will find  that  the  image is at the same distance behind the mirror as the object is in front of it. Now verify this by placing the object anywhere on the chart paper.