What is LIGHT?

WHAT IS LIGHT?

Electromagnetic radiation waves

*Light waves are three dimensional.

*Light waves vibrate in all planes around a center line.

*The waves have high points called “crests.”

*Waves also have low points called “troughs.”

*The distance from one crest to the next crest is called a “wavelength.”

*The number of waves passing a given point in one second is called the “frequency.

NATURE OF LIGHT

Particle?

–        Newton

Wave?

–        Christian Huygens in Newton’s day

–        Thomas Young (1801)

•          Light can diffract - must be a wave

•          Transverse wave

PROPERTIES OF LIGHT

*Light travels in straight lines:

*Light travels VERY FAST – around 300,000 kilometres per second.

*At this speed it can go around the world 8 times in one second.

*Light travels much faster than sound. For example:

1)      Thunder and lightning start at the same time, but we will see the lightning first.

2)      2)  When a starting pistol is fired we see the smoke first and then hear the bang.

*We see things because they reflect light into our eyes.

LUMINOUS AND NON-LUMINOUS OBJECTS

A luminous object is one that produces light.

A non-luminous object is one that reflects light.

Properties of Light summary

1)      Light travels in straight lines

2)      Light travels much faster than sound

3)      We see things because they reflect light into our eyes

4)      Shadows are formed when light is blocked by an object