Shadows

D. Crowley, 2008

Shadows

To know how shadows are formed

Light

• What is light?

• How does it travel, and at what speed?

• How can we see objects?

• Do all objects give out light?

• Discuss what you know about light with your partner…

Light

• Light carries energy and travels as a wave

• Light travels extremely quickly - 300,000 km/s (much faster than sound - think about fireworks / thunderstorms)

• Light waves travel in straight lines (it cannot bend around corners)

Shadows

• Why do shadows form?

• Light travels in straight lines (it cannot bend around corners)

• Shadows form because light cannot bend round behind an object

Luminous

• Some objects are known as luminous

• A luminous object gives out light (a light source), such as: -• Fires• Light bulbs• Stars (e.g. the Sun)

Luminous

• How does light travel from a luminous object to our eye?

Light travels in a straight line, directly to your eye

Non-luminous

• Most objects are non-luminous

• A non-luminous object does not give out light

• We see non-luminous objects by light from a luminous object hitting the non-luminous object and reflecting into our eye

Non-luminous

• How does light travel from a non-luminous object to our eye?

Light from the luminous object hits the non-luminous object, reflecting light into our eye

Terms

• Opaque - materials which do not allow light to pass through them (e.g. a brick wall)

• Transparent - materials which do allow light to pass through them (e.g. a glass window)

• Translucent - materials which only allow part of the light to pass through them (e.g. paper)

Casting Shadows

• Complete the casting shadows worksheet

Casting Shadows

• Shadow of full milk bottle is much bigger, as no light is passing through (opaque)

• Drinking class is transparent, allowing light through (so shadow is just an outline, unlike the full shadow of the opaque mug)

• Empty cola bottle has only an outline shadow, unlike the full shadow of the full cola bottle

• If the lamp is raised the shadows become smaller

• If the lamp is lowered the shadows become bigger