Light Energy Chapter 5.4

Introduction to Light

Electromagnetic Spectrum Energy released from the sun is called electromagnetic radiation Most of the waves in the electromagnetic spectrum is invisible to us The waves are all different types of light, the only difference is their wavelength and frequency

Visible spectrum This spectrum is made up of different colours ROY G BIV Each colour has waves of slightly different lengths Red light has the longest wavelength and the lowest frequency Violet has the shortest wavelength and the highest frequency

Why does the ball look yellow? When sunlight hits the surface of the ball, it absorbs the all the energy from all parts of the spectrum EXCEPT YELLOW. Our eyes see only these REFLECTED colours and our brain recognises the ball as being yellow.

What happens to light energy? When light hits a surface, it may be: Reflected from the surface: that can be thought of as the light waves bouncing off the object it is hitting. White objects reflect ALL parts of the visible spectrum absorbing none. Absorbed into the substance: all the light energy that hits the object is taken in and changed into other forms of energy. Black objects absorb all parts of the visible spectrum reflecting none. Transmitted through the substance: Transparent or translucent objects will all light energy to pass through them

Luminous objects Objects that give out their own light We get to see luminous objects because their light enters our eyes directly Examples include: the sun, stars, glow-worms and fire-flies

Non-luminous objects Objects that do not give out their own light We get to see non-luminous objects because light is reflected from them and into our eyes Examples include: the moon, planets, trees and animals

Transparent objects Almost all light is transmitted through the substance A clear image can be seen through the substance Eg: glass, shallow water

Translucent objects Some light may be reflected, and light that passes through is scattered An image seen through the substance is fuzzy Eg: plastic bags, frosted glass, tissue paper

Opaque objects Light is either reflected from or absorbed into the substance No light is transmitted No image can be seen through the substance Eg: brick, wood, football, tree