PHYSICS [2 Mark Question Answer]

Luminous
The bodies which have the light of their own e.g. sun stars, bulb, candle, oil lamp, torch, a lantern.
Non-Luminous
The bodies-which do not have their own Light. e.g. moon, chair, table. When light falls on them, they become visible.

Eclipses are examples of the formation of shadows in nature.
There are two kinds of eclipses:

1. Lunar eclipse (the eclipse of the moon), and
2. Solar eclipse (the eclipse of the sun).
   A lunar eclipse is due to the formation of the shadow of the earth on the moon and solar eclipse is due to the formation of the shadow of the moon on earth.

At noon the sun is directly overhead. So, the sun rays fall vertically on the body. Hence the shadow is very short. In the morning and evenings, the sun rays fall in an inclined position. So, the shadows are long.

We do not see the shadow of a bird flying high up in the air because in their shadow, the umbra is absent and the penumbra is too large and too faint that it is not visible as the distance of screen (i.e. earth) is very large from the object (i.e. bird).

If the size of the source of light is bigger than the size of the opaque object, the size of the umbra is very small. If the screen is moved away from the object, the umbra vanishes and only the penumbra remains.

EF is Penumbra CD is umbra.

A’B’ – umbra
Umbra alone is obtained on the screen when the opaque object is illuminated by a point source of light.

Formation of umbra alone.

When light falls on an opaque object, light is obstructed and a dark patch on a screen kept behind is called a shadow. This is because light propagates in straight line. If the distance between the object and screen is less, the shadow will be (umbra) dark and smaller.
If the distance is increased shadow will be dim and larger.

If the hole is bigger than a pinhole, again a blurred image is seen. The reason is that a bigger hole is equivalent to a large number of pinholes. Each pinhole produces one image. These images overlap each other resulting in a blurred image.

If another pin hole is made near the first pin hole, two images are formed on the screen, one due to each of the two pin holes. If the holes are very close, the two images tend to overlap each other. As a result, a blurred image will be seen.

Image obtained in a pinhole camera is inverted.
The reason is that the light travels in a straight-line path. Hence light from the upper point of the candle passes through the pinhole and strikes the tracing paper in the lower point. Similarly, light from the lower point of the candle passes through the pinhole and strikes the tracing paper at the upper point.

Factors affecting the size of the image :
The size of the image depends on the following two factors:

1. The distance of screen (i.e. tracing paper) from the pinhole, and
2. The distance of the object (i.e. candle) in front of the pinhole.

We can see the light of the bulb in the arrangement (a).
This is so because in arrangement ‘a’ the rod is straight and light travels in a straight-line path.
Whereas in arrangement ‘b’ the rod is bent. So the light cannot pass through it.

No, a transparent medium cannot form an image. All the light that passes through a transparent medium completely passes through the substance. For the formation of the image, it is just that the light rays get reflected through the surface.

A solar eclipse occurs when the moon comes in between the Sun and the Earth and casts its shadow on the earth. In such a case, the moon being smaller in size casts its shadow only on a limited region on the earth.