☰ Year plan · Science

Light, sight and night eyes

Week 6 · Axis 1, Unit 1 Living Systems, Concept 1.3 Light and Sight (A) · 3 lessons
1

Light and how we see

Discovery Education Science P4: Term 1, Unit 1, pp. 58–69
GoalExplain that light travels in straight lines and that we see things when light enters our eyes.
New words
light source · something that gives out its own light, such as the Sun or a lampstraight line · a line that does not bendreflect · when light bounces off an object
Explanation

Light is a kind of energy that travels from one place to another. Things that give out their own light are light sources: the Sun, a lamp, a torch, a Ramadan lantern with a bulb. Light travels in straight lines. We see a light source when its light goes straight into our eyes. Most things are not light sources, such as a book, a ball or the Moon. We see them because light from a source hits them, bounces off in all directions, and some of it enters our eyes. In a completely dark room, nothing can be seen, because there is no light to bounce and nothing to enter the eyes. Never look straight at the Sun, because its light is strong enough to hurt your eyes.

Light sourcesNot sources: we see them by reflected light
Worked examples
Omar switches on a torch in a dim room and points it at the wall. The beam goes straight from the torch to the wall. It does not bend round the corner.
Salma reads a book by a window. Light from the Sun goes through the window, hits the book, bounces off and enters her eyes. That is how she sees the page.
A lamp lights a teddy bear. Light goes from the lamp to the teddy, bounces, and goes into the eye. The arrows show the path of the light.
Class activity

Shadow shapes. In a dim room, a grown-up holds a torch pointing at a wall while you hold a toy between the torch and the wall. Look at the shadow. Move the toy nearer the wall, then nearer the torch. What happens to the shadow? Light travels in straight lines, so it cannot bend round the toy. Never shine the torch toward anyone’s eyes, and never look at the Sun.

Practice
1
Is a candle flame a light source? Is the Moon?
2
In the picture, follow the arrows. Which object gives out its own light?
3
Why can you not see anything in a completely dark room?
4
Why must we never look straight at the Sun?