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ShadowsToday’s learning objective is to:

• Analyse how shadows occur and what affects their size.

Starter:

• BACK OF BOOK: List the variables which you think will affect how big a shadow is.

19 April 2023

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Key words• Shadow

• Umbra

• Penumbra

• Luminous

• Non-luminous

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Investigating shadowsUse the practicals to identify the nature of how light travels and what causes shadows. You will need to write a conclusion of what you found.

Extension: Can you draw a diagram of what is happening to form the shadow?

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• A shadow is a dark area or shape produced by a body coming between rays of light and a surface

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Investigating shadows

Umbra – dark shadow

Penumbra – pale shadow

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Investigating shadows• Cut out a shape from a

piece of card and hold it between the lamp and your exercise book.

• Look closely at the shadow• What happens to the size

of the shadow if you move the card closer to or further from the lamp?

• Is the shadow all the same colour?

• Sketch a diagram of the shadow.

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Today’s…

Today’s learning objectives were to:

• Explain how we see luminous and non-luminous objects.

• Explain why shadows occur and what affects their size.

Self-assess your understanding of these learning

objectives.

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Have you ever wondered?

• How have ideas about light changed?

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Speed of light

• As soon as you turn on a lamp you can see the light.

• Galileo Galilei (1564-1642) was an Italian scientist who tried to measure the speed of light but it is too quick.

• Olaus Roemer (1644-1726) was a Dutch astronomer. He observed moons orbiting Jupiter and was able to calculate the speed of light as 241,000km/s.

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Speed of light

• Armand Fizeau (1819-1896) and Leon Foucault (1819-1868) measured the speed of light reflected from a mirror 8km away as 313,000km/s.

• Foucault improved the experiment and measured the speed of light as 298,000km/s

• Modern experiments measure the speed of light as 299,792km/s

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Speed of light

Complete one of the following worksheets:

• 8Ka(1) Travelling light (SUPPORT)

• 8Ka(6) Bonfire night (SUPPORT)

• 8Ka(7) Speeding light (CORE)

• 8Ka(5) Jupiter’s clock (HIGHER)

Extension

• 8Ka(4) Lighthouses

• 8Ka(8) More light measurements

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Answers to worksheets8Ka(7)1, 2

3 a 4 kilometresb 24 secondsc rays drawn correctly with arrows in correct direction

4 4 years5 8.5 × 5 = 42.5 minutes6 8.5 + 4.25 = 12.75 or 13 minutes to the nearest minute7 between 8 and 9 minutes, on average, the Moon is the same distance

from the Sun as the Earth is

Sun

Earth

Moon

Luminous source

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Answers to worksheets8Ka(5)1 Telescopes are more powerful today.2 a Total distance = 4 km, time = 4/300 000 = 0.000 013 3 seconds (or 1.33 × 10–5

seconds).b 0.000 026 7 seconds (2.66 × 10–5 seconds), or double the answer to part a, if that was incorrectc The difference between the two times is far too small to be measured by any instruments that Galileo could have had.

3 a Light has a shorter distance to travel from Jupiter to E1, and further to travel to E2.b The additional positions should be above and below the Sun.

4 His calculation depended on knowing an accurate value for the radius of the Earth’s orbit. This value was not known accurately at that time.

5 a 16 minutesb time = 16 × 60 = 960 secondsdistance = 2 × 149 600 000 km, = 299 200 000 km = 299 200 000 000 m (or 299 × 109 m)speed = 299.2 × 109/960 = 3.12 × 108 m/sc The 8 minutes may not be exact, or the radius of the Earth’s orbit may be an approximation.

6 a position approximately 30º from the one shown (360º/11.86)

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Answers to worksheets8Ka(8)1 a The time was the difference in the eclipse times for Jupiter’s moons. The distance

was the diameter of the Earth’s orbit.b We have a much more accurate value for the diameter of the Earth’s orbit, and we also have more accurate ways of measuring time.

2 It showed that light took time to travel.3 the speed of the Earth in its orbit, and the tiny angle through which the positions of

stars appeared to move4 a the speed the wheel was spinning, the width of the teeth and gaps on the wheel,

and the distance between his wheel and the mirror that reflected the light backb To make the time interval longer, and so a little easier to measure accurately. A very good answer will point out that a certain error is a smaller proportion if the value itself is larger.

5 the speed his mirror was spinning, the angle of the reflected light, the exact distance the light had travelled

6 They could have written to other scientists or to scientific societies, or they could have written papers or books for publication. Do not accept answers involving emails, etc.!