Light in straight lines
A ray is a straight line with an arrow: the path of light.
Three cards and a torch
A torch shines towards a wall. In between stand three cards, each with a small hole.
When will the torch light reach the wall?
What this lesson covers
The idea
Light travels along straight lines and is represented by rays, straight lines with arrows that show the path along which light travels.
Three cards and a torch
A torch shines towards a wall. In between stand three cards, each with a small hole.
When will the torch light reach the wall?
- When all three holes are in one straight line
- Whenever the first hole is in front of the torch
- Always: light bends around the cards
Line up the holes
Card 2 is out of line. Move it until the light reaches the wall. Then draw the ray that shows the path of the light.
Straight lines with arrows
Light travels along straight lines. It is shown by rays: straight lines with arrows that show the path along which light travels.
In the rest of this chapter, we draw rays to see what mirrors and lenses do to light.
- Part of a ray | What it shows
- The straight line | The path of the light
- The arrow | The way the light travels
Notes
Light travels along straight lines and is shown by rays: straight lines with arrows that show the path along which light travels.
Check yourself
Which drawing shows a ray of light correctly?
The light reached the wall only when the three holes were in one straight line. What does this show?
A ray goes from a lamp to a book. Which way does its arrow point?
- A wavy line with an arrow. Light travels along straight lines, so a ray is drawn straight.
- A straight line with an arrow — correct. Yes. The line shows the path, and the arrow shows the way light travels.
- A straight line with no arrow. Without an arrow, we cannot tell which way the light travels.
- The cards make the light. The light comes from the torch. The cards only block it or let it through.
- Light can bend around the cards. If it could, it would reach the wall even when card 2 was out of line.
- Light travels along straight lines — correct. Yes. Light cannot bend around a card to find the next hole.
- From the book towards the lamp. Light comes from the lamp, so the arrow points away from the lamp.
- From the lamp towards the book — correct. Yes. The arrow shows the way the light travels: from the lamp.
- Both ways at once. A ray has one arrow, pointing the way the light travels.