Light Travels in a Straight Line

Light Travels in a Straight Line

apter 5 Ch

왖 Beams of sunlight travel in straight lines.

Have you ever seen beams of sunlight streaming down through the clouds? A light beam is made up of many light rays. A thin line of light energy is called a light ray. Light beams and light rays always travel in straight lines. This explains why shadows form behind objects. Shadows form when an object blocks a light beam. NEL

왖 Why is there a shadow here?

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Observe How Light Travels Skills Focus: observing, measuring, inferring 1. On four index cards, draw lines from corner to corner to make an X. Make a hole at the centre of the X with a hole punch.

For a review on measuring length, see the Skills Handbook, page 228.

2. Stand the index cards up on a table using small lumps of modelling clay. Place the cards about 10 cm apart and try to make sure the holes are in a straight line. 3. Put a flashlight 10 cm from the first card. Turn on the flashlight. If needed, put the flashlight on a book to make sure the light goes through the holes.

4. Ask your teacher to darken your classroom. Can you see the light coming through the last hole? If not, adjust your cards. What does the light beam look like? Spray a fine mist of water along the light beam to make it show up better.

5. Move one card out of line. Can you still see the light shining through the last card? Explain what you see to a partner.

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NEL

Offer opinions about what you have read. Do you think sundials have any advantages over modern clocks? Compare your opinion with a partner.

Before clocks were invented, people used shadows to tell the time. Sundials are made of an arm that casts a shadow on a base. Times are labelled around the base. As Earth spins, the Sun appears to travel across the sky. The shadow made by the arm of the sundial moves as the position of the Sun in the sky changes.

noon afternoon

morning arm

base

1. In what type of path does light travel? 2. Why do you see shadows? 3. Why are there no shadows on faces when we take a picture using a camera flash?

NEL

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