Light, Shadows, and Reflection

Luminous objects –

Objects that emit light of its own.

Example – Sun,stars,torch etc.

Transparent, Opaque and translucent objects-

Transparent object-

• which allow light to pass through them and
• we can clearly see through them.

Example- Window glasses.

Translucent objects-

Objects through which we can see, but not very clearly.
Example- Paper sheet with oily patches.

Opaque object –

Objects through which we cannot see.
Example- cardboard, wood.

Shadows –

• The dark patch formed by objects on the ground or any screen.
• The ground, wall of the room, a building, or other such surfaces act as a screen for the
  the shadow you observe in your daily life.

A Pinhole camera –

Use the point of a sharp pencil to punch a hole in one of the shorter ends of the box. Use a knife to cut a square in the opposite end of the box, directly across from the hole. Use scissors to cut a square of wax paper Place the wax paper directly over the square you cut in the box. Tape the edges of the wax paper to the box. Cover your head and pinhole camera with a blanket. Be sure that the end with the wax paper is facing you and the end with the pinhole is facing the lamp. Hold your pinhole camera at arm’s length from your face and aim it at the lamp. Keep it steady until you see an upside-down image of the lamp.

Reflection –

Bouncing back of light on striking any smooth and shiny surface.

Properties of light-

•Light travels in a straight line.
•Light gets reflect from a mirror.

Mirror-

Shiny or smooth object through which light bounces back.

Exercise

1. Rearrange the boxes given below to make a sentence that helps us understand opaque objects.

2. Classify the objects or materials given below as opaque, transparent or translucent and luminous or non-luminous: Air, water, a piece of rock, a sheet of aluminum, a mirror, a wooden board, a sheet of polythene, a CD, smoke, a sheet of plane glass, fog, a piece of red hot iron, an umbrella, a lighted fluorescent tube, a wall, a sheet of carbon paper, the flame of a gas burner, a sheet of cardboard, a lighted torch, a sheet of cellophane, a wire mesh, kerosene stove, sun, firefly, the moon.

Answer :

Opaque-  a piece of rocks, a sheet of aluminum, A CD, smoke,Iron, an umbrella, a wall.

Transparent- Air, water, a sheet of plane glass,

Translucent- A sheet of polythene, Fog, a sheet of cellophane

Luminous- A lightened fluorescent tube, the flame of a gas burner, a lighted torch, Firefly, Stove, sun, moon

Non-luminous- A mirror, a piece of rock, a wire mesh, iron, a wall

3. Can you think of creating a shape that would give a circular shadow if held in one way and a rectangular shadow if held in another way?

Answer :
Yes, we can think of creating a shape that would give a circular shadow if held in one way and a rectangular shadow.
Example-circular dice, cylinder.

4. In a completely dark room, if you hold up a mirror in front of you, will you see a reflection of yourself in the mirror?

Answer :
No, in a dark room, we will not see a reflection of ours. As in the dark room, the light will not fall on the mirror, and the phenomenon of reflection will not take place.