Compare day and night in terms of the spinning of the Earth. Use models to demonstrate and explain the seasons.
The Sun is the closest star to the Earth. The temperature at the centre of the Sun is approximately 14 million °C. Reactions in the Sun change nuclear energy into light and heat energy that falls onto the Earth.
Light
The light energy we get from the Sun is useful as it is changed into other forms of energy. For example, plants convert energy from the Sun into chemical energy during photosynthesis.
A luminous object transforms and emits its own light, such as stars, a light bulb or a candle. An object is luminous only when it is transforming and giving out light. For example, when a light bulb is turned off it is non-luminous.
Non-luminous objects reflect light from other sources. You can read the words on this page because light from another source is reflecting off the book and entering your eyes.
Learn more about bouncing light and how we see objects in Physical World 19.2
Materials can be described in three ways in relation to light:
1. Transparent: allows light to pass through with no shadows formed. For example, a clear window.
2. Translucent: allows only some light to go through (not all) and forms a shadow that is very light. For example, a stained-glass window.
3. Opaque: allows no light to pass through and forms a shadow. For example, a table, chair or a human.
How does light travel?
1. Set up the investigation in Fig. 23.1.3. Predict what will happen when the student moves card B to the left.
2. Carry out the investigation. What happens? Why does this happen?
z Fig. 23.1.3 401 401 A Transparent z Translucent
Fig. 23.1.2 Materials in relation to light
B C Opaque A z B
Fig. 23.1.1 The Sun
C
23.1
Key Words Luminous
Non-luminous Transparent Translucent Opaque Shadow Season
