Light

Some basic information on light Light is the fastest thing in the universe. It moves at… 300 000 000 m/s Other speeds in m/s: Sound: 343 m/s Car on highway: 28 m/s You running: 7.5 m/s

Light versus sound Explain why you see lightning before you hear thunder during a thunderstorm.

Light versus sound Why do you see a firework explode before you hear the explosion?

What is a lightyear? This is a unit of distance. It tells us how far light can travel in one year. This is very useful for measuring extremely long distances because light travels VERY fast and a year is a LONG time! 1 lightyear = 9 460 000 000 000 000 m

Light Light is a form of energy, meaning that it has the ability to do work. Light travels in waves, which propagate in a straight line.

Anatomy of a wave

Definitions: Crest: The top parts of a wave. Trough: The low points of a wave. Amplitude: The height of a wave from its rest position. In light, this is its brightness.

Definitions Wavelength: The distance between any two adjacent crests (or troughs). In light, this affects its colour.

Definitions Frequency: This the number of crests (or troughs) that pass by in 1 second. It is measured in “cycles per second”, or Hertz (Hz). If you see 100 crests in 25 seconds, what’s the frequency? ___ 500 crests in 2.5 seconds, what’s the frequency:

For light waves, the wavelengths are small These wavelengths are so small that they’re usually measured in nanometers (1 nm = 0.000000001 m) The colours we can see are: Red 700 nm Orange 600 nm Yellow 580 nm Green 540 nm Blue 470 nm Indigo 450 nm Violet 425 nm

Electromagnetic spectrum

Some non-visible radiation Longer wavelength Shorter wavelength Radio Micro- Infrared Visible UV X-rays Gamma waves waves rays light rays rays

Different wavelengths: The shorter the wavelength, the more energy the wave carries. But it can’t travel far. The longer the wavelength, the less energy the wave carries. But it can travel further.

Electromagnetic waves Electromagnetic waves (light, X-rays, microwaves, etc) do not need a medium (material) to travel through. Other waves do need a medium: Water waves require water as a medium. Sound waved require air as a medium.

Greenhouse Effect

White Light White light is made up of all the colours. We can separate it into its colours by using a prism:

White light We don’t see objects… we see light reflecting off objects. Different objects reflect specific wavelengths of light. All other wavelengths of light are absorbed.

White and Black White objects reflect all wavelengths of light. Black objects absorb all wavelengths of light

Should you wear white or black?

Fill in your table (TRANSPARENT) What happens when light strikes a transparent material? Examples of materials:

Fill in your table (TRANSLUCENT) What happens when light strikes a translucent material? Examples of materials:

Fill in your table (OPAQUE) What happens when light strikes an opaque material? Examples of materials:

Drawing Cloud Yellow traffic light White car Black tire Clear glass window

Angle of Incidence and Reflection The normal is an imaginary line that is perpendicular to the surface. The angle of incidence is the angle the ray of light makes with the normal. It is the same as the angle of reflection.

When light reflects off an object (such as a mirror), it bounces back at the exact same angle that it hit.

Refraction When light passes through a different medium, it can be bent. This is called refraction. The angle of incidence is smaller the same as the angle of refraction.

Refraction

Different mediums change the angle of light.

What happens when you put light through a convex lens?

What happens when you put light through a convex lens?

What happens when you put light through a convex lens?

What happens when you put light through a concave lens?

What happens when you put light through a concave lens?

What happens when you put light through a concave lens?

Your eye works the same way

How your eyes work

How your eyes work

Review Question What is the focal point of a lens?

How your eyes work

How your eyes work

Myopia (focal point before retina)

Myopia (focal point before retina)

Hyperopia (focal point after retina)

Hyperopia (focal point after retina)