# Glass and light

```Friday, 15 September
2023
B2 Lesson 3
Learn the terminology behind different
types of glass and their relationship to
light. Study concave and convex lenses.
How can I classify materials
depending on how much light the
let through?
Transparent
• If a material is transparent it will let light
into a room and the light rays will not be
scattered.
Translucent
• Translucent materials normally have irregular
surfaces and the light rays are scattered as
they pass through. That is why you don’t see a
clear image.
Opaque
• Opaque materials do not let light to pass
through. All light rays are absorbed.
page 198
Complete activity 9 from the
booklet
Refraction
The speed of light depends on the material through
which the light is travelling.
When light enters a different material (e.g. from air
into glass), the speed of light changes.
This causes the light to bend or refract.
air
glass
The speed of light is affected by the density of the material
through which it is travelling.
When light enters a more dense material, its speed
decreases and this is why refraction occurs.
Concave lenses
Diverging or concave lenses refract the parallel rays
of light so that they spread apart from one another.
Refraction in a glass block
Lenses
Lenses work by refracting light at a glass-air
boundary.
Although refraction occurs at the
boundary, we will treat all lenses as bending the
rays at the lens axis.
Convex Lens
Convex or converging lens make rays of light come together,
or converge.
Page 203
Complete activities 10 -11
```