PHYSICS [1 Mark Question Answer]

A medium that allows the passage of light through it easily is called a transparent medium.
Examples: glass, air, water, etc.

Luminous object.

The bodies that shine on its own or which themselves emit their own light are called the luminous bodies.

Moon is not a luminous body, it is a non-luminous body. It has no light of its own.

Electric bulb, torch, an oil lamp, fluorescent tube, candle.

Sun, stars, jugnu, firefly.

When the length of the pinhole camera is increased. C is the screen is moved away from the pinhole, the size of the image also increases.

If the object is moved towards the pinhole the size of the image increases.
The size of the image / The size of object = Distance of screen from pinhole / Distance of object from pinhole

An object becomes visible to us when the light after striking the object reaches our eyes. Light itself is not visible, but the light makes objects visible to us.

The simple applications of rectilinear propagation of light are pinhole camera, the formation of shadows, and elipses.

Take three cardboards A, B, and C each about 25 cm square. Take a pin and make a small hole in each cardboard at the same height. Suspend the cardboard pieces by separate threads vertically from support such that each hole is at the same height, as shown. Pass a string through the holes and pull it taut. This makes the three holes in a straight line. Now take out the string.
Place a lighted candle near one of the cardboards (say A). Look at the candle flame from the other side of the cardboard C. The candle flame is clearly seen.
Now slightly displace one of the cardboards (say B) so that the holes no longer remain in a straight line. Again look at the candle flame from the other side of the cardboard C. You do not see the candle flame. The reason is that light travels in a straight line and now the holes in the cardboards A, B, and C are not in a straight line.
Conclusion:Light travels in a straight line path called the rectilinear propagation of light.

Light travels in a straight-line path. This is called the rectilinear propagation of light.

A substance through which light passes is called a transparent substance.
Examples: glass, air, water, etc.

A substance through which we cannot see light is called an opaque medium.
Examples: Wood, metals, butter paper, and black paper, etc.

Light is a form of Energy i. e. The external physical cause that affects our eye to produce the sensation of vision.

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.

Whenlightfallsonanopaqueobject, light is obstructed and a dark patch on a screen kept behind is called the shadow. This is because light propagates in a 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.
Conditions Required for a shadow to form are:

1. There should be a source of light.
2. An opaque object.
3. A screen.
4. The opaque object is placed between the source of light and the screen.

Moon, jugnu.

Water, glass.

The measurement of the brightness of the light is called luminous intensity.
One lumen is considered to 1 / 1256 th of candle power.

Electric bulb, torch, an oil lamp, fluorescent tube, candle.

Sun, stars, jugnu, firefly.

To see the Solar Eclipse Safely:
Take a cardboard or X-Ray film and make a small hole in it. Place it in front of a wall. Through the hole, the image of the Sun will be formed on the wall. This image we can see with an eye. We are not looking at the Sun directly, so there will be no harm to the eyes.

Light is a form of Energy i.e. The external physical cause that affects our eye to produce the sensation of vision.

Jugnu, firefly.

To measure the brightness of light in comparison with the brightness of a candle. The unit of candle power is used.

Glass, water, air, etc.

Jugnu and firefly.

Any burning thing emit light. The intensity of the light may not be the same. A flame of a gas stove emits light.

When the light falls on an object, it scatters even if the sunlight does not enter a room. due to scattered light., the object becomes visible.

1. An electric bulb
2. Candle
3. An oil lamp
4. A torch