Transparent, translucent and opaque

Three ways of letting us see

Some materials let us see right through them, some only blur the view, and some block it completely.

• Transparent materials let us see through them clearly: glass, water, air and cellophane paper.
• Translucent materials let us see through them, but not clearly: frosted glass, which has a hazy surface, and butter paper.
• Opaque materials do not let us see through them at all: wood, cardboard and metals.

Hide-and-seek

In the chapter, Ghulan hides behind a wall, Sheeta behind a big tree and Sara behind a frosted glass door, while Sheeta’s younger brother watches through the glass window of his house.

Where	Kind of material
A: Ghulan, behind a wall	Opaque
B: Sheeta, behind a tree	Opaque
C: Sara, behind frosted glass	Translucent
D: the brother, at a glass window	Transparent

Ghulan and Sheeta chose opaque things so that they could not be seen at all; Sara’s frosted glass hid her only partly, since her shape showed as a blur. If the brother’s window were wooden and closed, he could not see them, because wood is opaque.

Classifying everyday objects

Object	Kind
Glass tumbler	Transparent
Window glass	Transparent
Butter paper	Translucent
Frosted glass	Translucent
Eraser	Opaque
Wooden board	Opaque

Can water change?

Clear water is transparent: we can see a coin at the bottom of a glass of water. Stir in a little milk or mud and the water turns cloudy and translucent; with a lot of mud or ink it becomes opaque.

Try it yourself

Collect a glass sheet, a clear plastic bag, cellophane, butter paper, tissue paper, cloth, cardboard and a steel plate. Hold each one between your eyes and a lamp or a window, and sort them into the three groups. You will find that the same material can change group with its thickness: one layer of tissue paper lets you see shapes, while a thick pad of it hides them completely. (Extra: a drop of oil on plain paper turns that spot translucent, which is why oily food leaves see-through patches on paper bags.)

Why we see through some things (Extra)

We see an object when light from it reaches our eyes. A transparent material lets almost all of that light pass straight through, so the picture stays sharp. A translucent material lets light through but scatters it in many directions, so the picture becomes a blur. An opaque material stops the light, so we cannot see what is behind it.

Using each kind

• Transparent: windows that let light and the view in, spectacles, and glass or plastic jars in shops and kitchens, so that we can see the contents and how much is left.
• Translucent: frosted glass in bathroom windows and doors, which lets light in but keeps privacy, and butter paper for tracing.
• Opaque: walls, doors, curtains and boxes, which block the view and keep things private.

To read about other properties, see properties of materials. For the textbook’s questions, see the Chapter 6 NCERT solutions; for the whole chapter, see the Chapter 6 notes.