Right Or Left

RIGHT OR LEFT!

When you see your image in a plane mirror, is it exactly like you? Have you ever noticed that there is one interesting difference between you and your image in a mirror? Let us find out.
 

Activity 15.4

Stand in front of a plane mirror and look at your image. Raise your left hand. Which hand does your image  raise (Fig. 15.8)? Now touch your right ear. Which ear does your hand touch in your image? Observe carefully. You will find that in the mirror the ‘right’ appears ‘left’ and the ‘left’ appears ‘right’. Note that only sides are interchanged; the image does not appear upside down.Now write down your name on a piece of paper and hold it in front of a plane.

Can you now understand why the word ‘AMBULANCE’ is written as in Fig. 15.9 ? When the driver of a vehicle ahead of an ambulance looks in her/his rear view mirror, she/he can read ‘AMBULANCE’ written on it and give way to it. It is the duty of every one of us to allow an ambulance to pass without blocking its way.

Spherical Mirrors

You might have observed that in the side mirror of a scooter or a car the images of all the objects appear smaller than the objects themselves. Have you ever wondered why is it so?

PLAYING WITH SPHERICAL MIRRORS

Paheli and Boojho were waiting for their dinner. Boojho lifted a stainless steel plate and saw his image in it. Oh! This plate acts as a plane mirror. My image is erect and is of the same size. Paheli saw her image using the back of a steel spoon. “Boojho look here! I can also see my erect image though it is smaller in size. This spoon also acts as a mirror of some kind”, said Paheli.

You can also use a spoon or any curved shining surface to see your image

Activity 15.5

Take a stainless steel spoon. Bring the outer side of the spoon near your face and look into it. Do you see your image in it (Fig. 15.10)? Is this image different from what you see in a plane mirror? Is this image erect? Is the size of the image the same, smaller or larger

Now look at your image using the inner side of the spoon. This time you may find that your image is erect and larger in size. If you increase the distance of the spoon from your face, you may see your image inverted (Fig. 15.11). You can also compare the image of your pen or pencil instead of your face.

The curved shining surface of a spoon acts as a mirror. The most common example of a curved mirror is a spherical mirror.

Introduction to Concave and Convex Mirrors

If the reflecting surface of a spherical mirror is concave, it is called a concave mirror. If the reflecting surface is convex, then it is a convex mirror (Fig. 15.12).

Why are concave and convex mirror called spherical mirrors?

Take a rubber ball and cut a portion of it with a knife or a hack- saw blade [Fig. 15.13 (a)]. (Be careful. Ask an elder person to help you in cutting the ball). The inner surface of the cut ball is called concave and the outer surface is called convex (Fig. 15.13 (b)).

Fig. 15.13 A spherical mirror is a part of a sphere

The inner surface of a spoon acts like a concave mirror,while its outer surface acts lie a convex mirror.

Concave Mirror

We know that the image of an object formed by a plane mirror cannot be obtained on a screen.Let us investigate if it is also true for the image formed by a concave mirror.

Take a concave mirror. Hold it facing the Sun. Try to get the light reflected by the mirror on a sheet of paper. Adjust the distance of the paper until you get a sharp bright spot on it (Fig. 15.14). Hold the mirror and the sheet of paper steady for a few minutes. Does the paper start burning?

This bright spot is, in fact, the image of the Sun. Notice that this image is formed on a screen. An image formed on a screen is called a real image. Recollect that in Activity 15.2 the image formed by a plane mirror could not be obtained on a screen. Such an image is called a virtual image.

Now let us try to obtain on the screen the image of a candle flame formed by a concave mirror.

Activity 15.7

Fix a concave mirror on a stand (any arrangement to keep the mirror steady would do) and place it on a  table (Fig. 15.15). Paste a piece of white paper on a  cardboard sheet (say about 15 cm × 10 cm).

Fig. 15.15 Real images formed by a concave mirror

This will act as a screen. Keep a lighted candle on the table at a distance of about 50 cm from the mirror. Try to obtain the image of the flame on the screen. For this, move the screen till a sharp image of the flame is obtained. Make sure that, the screen does not obstruct the light from the candle falling on the mirror. Is this image real or virtual? Is it of the same size as the flame? Now move the candle towards the mirror and place it at different distances from it. In each case try to obtain the image on the screen. Record your observation in Table 15.1. Is it possible to obtain the image on the screen when the candle is too close to the mirro(Fig. 15.16)?

We see that the image formed by a concave mirror can be smaller or larger in size than the object. The image may also be real or virtual.

Concave mirrors are used for many purposes. You might have seen doctors using concave mirrors for examining eyes, ears, nose and throat. Concave mirrors are also  used  by  dentists to see an enlarged image of the teeth (Fig. 15.17). The reflectors of torches, headlights of cars and scooters are concave in shape (Fig. 15.18)

Convex Mirror

Boojho observed his image in the shiny surface of the bell on his new bicycle.He found that his image was erect and smaller in size.He wondered if the bell is also a kind of spherical mirror. Can you recognise the type  of the mirror?

Note that the reflecting surface of the bell is convex mirror?

Repeat Activity 15.7 now with a convex mirror in place of a concave  mirror (Fig. 15.19). Record your observations in a Table similar to Table 15.1.Could you get a real image at any distance of the object

Did you get an image larger in size than the object?

Can you now recognise the mirrors used as side mirrors in automobiles? These are convex mirrors. Convex mirrors can form images of objects spread over a large area. So, these help the drivers to see the traffic behind them (Fig. 15.20)