Introduction to Light

Let there be light!

Last lesson we learned that heat can travel in three ways- conduction, convection and radiation.
Radiation was the form that did not require a medium or matter to make it from on place to another
Radiation was an electromagnetic wave
Light is an example of electromagnetic radiation

What is a wave?

A wave is periodic motion
-ocean waves are examples
-sound waves are another example

A wave will have
SPEED: how fast it is going
FREQUENCY: how often the highs and the lows will occur
WAVELENGTH: how long it is before it repeats itself

The higher the frequency, the shorter the wavelength






The lower the frequency, the longer the wavelength

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Multiple Choice

Loud sounds will have

• higher amplitude

• lower amplitude

• faster speeds

• lower speeds

Labelling

Label the parts of the wave

Drag labels to their correct position on the image

trough

crest

amplitude

wavelength

Poll

Which is faster, the speed of a sound wave or the speed of a light wave?

• SOUND

• LIGHT

Poll

The speed of which wave is constant (doesn't change)

• Light

• Sound

Poll

Which waves need a medium (matter) in order to go from one place to another?

• Sound Waves

• Light Waves

Light and its many wavelengths

When light is passed through a perspex prism ( or a diamond!) it splits into its many wavelengths, giving us the colours of a rainbow

The wavelengths are very small in size, typically in the hundreds of NANOmetres (10^-9=0.000000001)

What colour you end up seeing, depends upon the ANGLE at which the light enters the object and leaves.

​The higher the "refractive index", the better the light splitting.
When light enters a glass or perspex boundary, it bends or refracts.
When it bounces off a surface, it reflects.

What waves can do

Reflect: bounce off a boundary
Refract: bend when entering a new medium
Diffract: spread out once they enter a very narrow opening
Absorbed: can be prevented from travelling further by certain materials
Transmitted: can be passed through materials

Light can also be scattered

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The Wave Equation

Multiple Choice

The wave equation is given by $$v=f\times\lambda$$ . If the frequency is 4Hz and the wavelength is 12m. Determine the speed

• 48m/s

• 3m/s

• 16m/s

• 8m/s

Multiple Choice

If the wave equation is given by $$v=f\times\lambda$$ , determine the frequency if th speed is 10m/s and the wavelength is 5cm

• 200 Hz
• 50 Hz
• 2 Hz

• 20 Hz

Reorder

Reorder the following waves in increasing frequency

• radio waves

• microwaves

• visible

• ultraviolet

• X-ray

1

2

3

4

5

• 1
• 2
• 3
• 4
• 5

Match

Match the definitions to the words

• reflection

• refraction

• diffraction

• absorption

• transmission

waves bouncing off a boundary

waves bending as they pass through different mediums

waves spreading out after passing through a narrow opening

waves being taken in by a material

waves passing through a material without being absorbed

• waves bouncing off a boundary

• waves bending as they pass through different mediums

• waves spreading out after passing through a narrow opening

• waves being taken in by a material

• waves passing through a material without being absorbed

Poll

Select all that apply to what you learned today-

I learned that

• light is made up of waves

• sound is made up of waves, but they are different to light waves

• when white light refracts, it splits into different colours

• all waves have frequency and a wavelength