Light and Shadow
FoundationLight comes from the sun and lamps; block it and shadows form, and sunlight hides seven colours.
- The sun, lamps and flames are all light sources.
- Light is used for lighting, reading and traffic signals.
- Opaque objects block light; shadows form on the side away from the light.
文體小知識：探究記敘一邊玩一邊學：手影遊戲裏藏著光和影子的科學道理。
§Text Passage
1Our world is full of light. Light comes from light sources: in the daytime the brightest source is the sun; at night we switch on lamps and torches, and candle flames glow too. With light we can see things; in a pitch-dark room we can see nothing at all.
2Light has many uses in life: lamps light up our homes so we can read and write at night; traffic lights use coloured light to direct traffic; doctors use a torch light to check our bodies. Reading needs enough light so the eyes do not tire, so a desk lamp is a good study friend.
3When light meets an opaque object, it is blocked, and where light cannot reach behind the object a shadow forms. Stand in the sun and a dark shadow follows you; at night put your hands between a lamp and the wall and hand shadows appear. A shadow always falls on the side away from the light.
4Sunlight looks white, but it hides light of many colours. After rain, drops of water in the sky spread sunlight into red, orange, yellow, green, blue, indigo and violet — a rainbow. Soap bubbles and the back of a CD also show colourful light.
5Light gives us brightness, but use it with care: never stare at the sun or strong light, or the eyes may be hurt; switch off the lamp after shadow games to save energy. Knowing light and shadows, play hand-shadow games at night and watch tree shadows by day — science is all around!
1Summary 重點摘要
Light comes from the sun and lamps; block it and shadows form, and sunlight hides seven colours.
2Vocabulary cards Vocabulary
The energy that lets us see; it comes from light sources.
Something that shines by itself, like the sun and a lamp.
The brightest light in the daytime, the main source of light and heat for the earth.
A hand lamp for walking at night and blackouts.
Making a place bright with light.
The dark shape made when light is blocked by an opaque object.
Not letting light pass, so it makes a shadow.
The band of seven colours made when sunlight is spread by water drops.
Something that glows when burning; a man-made source — beware of fires.
A game of making shadow shapes with hands between a lamp and the wall.
3Step by step Steps
- Step 1: Find the sources of lightWhere does light come from? In the daytime the sun shines over the land; at night lamps, street lights and torches glow; during a blackout a candle flame can light the room. Things that shine by themselves are called light sources. Mirrors and the moon look bright, but they only reflect light from elsewhere, so they are not sources. Search your home and classroom for more light sources.
- Step 2: Uses of light in our lifeThe greatest use of light is lighting: lamps make streets, classrooms and homes bright, so we can read and write at night. Traffic lights use red, yellow and green light to guide cars and people; doctors shine a small torch to check our throats; phone screens glow so we can see the pictures. Reading needs enough light; dim light tires the eyes, so turn on the desk lamp when studying.
- Step 3: Light and opaque objects make shadowsHow do shadows form? Light travels in straight lines; an opaque object blocks it, and where light cannot reach behind the object a dark shadow appears. Stand in the sun and the shadow follows; at noon when the sun is overhead the shadow is short; in the evening when the sun is low the shadow is long. Put your hands between a lamp and the wall and hand shadows appear at once — shadows always fall away from the light.
- Step 4: Changing the size of a shadowIn hand-shadow games you discover the secret: move your hands nearer the lamp and the shadow on the wall grows at once; move them farther from the lamp, closer to the wall, and the shadow shrinks. The size of a shadow depends on the distance between the object and the light. Change the angle of the lamp and the shadow turns too. That is why tree shadows differ in length as the sun moves — light is the prop of the shadow magician.
- Step 5: A rainbow hides in sunlightSunlight looks pure white, but it contains light of different colours. After rain, tiny water drops in the air spread the light into red, orange, yellow, green, blue, indigo and violet, hanging in the sky — a rainbow. Want a try? Stand with your back to the sun and spray a fine mist of water; you may see a small rainbow. Soap bubbles and the back of a CD also shine with seven colours.
- Step 6: Use light safely and treasure brightnessLight brings brightness but must be used with care: never look straight at the sun or a strong torch, for strong light hurts the eyes; switch off lamps after shadow games to save energy; light candles only with an adult, far from paper and curtains, to prevent fires. For night reading choose a soft, bright desk lamp. Now that you know light and shadows, go and try a shadow experiment!
5Worked example Example
Example: At night Mei and her brother play hand-shadow games. The brother's eagle shadow is small. How can Mei make the shadow twice as big, and why?
- Observe first: the shadow falls away from the lamp, and its size depends on the distance between the hands and the light.
- Move the hands nearer the lamp: the light spreads at a wider angle, and the shadow on the wall grows at once.
- To make the shadow smaller, move the hands farther from the lamp and nearer to the wall.
- Change the fingers too — spread the five fingers wide, and the eagle's wings grow broader.
- Answer: To make the shadow bigger, move the hands nearer the lamp, because the closer the hands are to the light, the more light they block and the bigger the shadow on the wall. Move the hands towards the wall and away from the lamp, and the shadow becomes smaller. Changing the distance controls the size.
6Common mistakes Mistakes
7Quick check Quick check
Q1What is the brightest light source in the daytime?
Q2How do shadows form?
Q3How can we make a hand shadow bigger?
Q4What are the seven colours of the rainbow?
Q5Why do we need enough light for reading?
8Recap Recap
- The sun, lamps and flames are all light sources.
- Light is used for lighting, reading and traffic signals.
- Opaque objects block light; shadows form on the side away from the light.
- Near the light the shadow grows; far from it the shadow shrinks.
- Sunlight holds seven colours; raindrops turn it into a rainbow.