18 / 09 Monday Kaupapa: Describe and explain the absorption of radiations in different surfaces

Do you remember? What are the seven electromagnetic radiations? What are the seven colours in the visible light? Which colour has the highest amount of energy? Why?

White

Remember: “ROYGBIV”

When a radiation hits a surface, three things can happen: Reflection (e.g. a mirror) Refraction (e.g. a window) Absorption (e.g. a wall)

When a radiation hits a surface or an object, three things can happen: __________ – the radiation bounces off (e.g. a mirror) __________ – the radiation travels through (e.g. a glass window) __________ – the radiation gets absorbed and warms up the surface (e.g. a wall)

Absorption

Pop Quiz: Why are they wearing white?

Demo: Heat Lamp

How do we “see” things? Luminous Object Non-luminous Object 13

Seeing Colours When visible light hits an opaque object, some colours are ________ and some are ________. The reflected colour is seen as the colour of the object.

Example: When a white light (containing all seven colours) reaches the object, only green colour is reflected and other colours are absorbed.

Why does the chick look yellow?

Why does the apple look red?

What about white? What about black?

Why do Bedouins wear black in the desert?

Absorption of light in White and Black A black surface ________ ALL colours, which is why it heats up fast when light is shone. A white surface ________ ALL colours, which is why it heats up much slower than a black surface.

Practical – Absorption of Light in Different Colours A metal can wrapped up with coloured paper

What have we learnt today? Why do many people wear white or light coloured cloths on a very sunny day?