Lasers: around the world in 0.1344 seconds, CBS talk 2015

Introduction
Public summary: 

What's the fastest way to send messages around the world? Find out in this talk!

Lasers: around the world in 0.1344 seconds, CBS talk 2015
Useful information
Kit List: 

Radio controlled car
Radio controlled helicopter
Paper aeroplane
Envelope

Red, green and blue class II laser pointers
Smoke machine

Blow up globe
Maglite torch

Tank of milky water
Plastic bottle with a hole in it, filled with milky water
Bucket

Red, green and blue lamps from CHaOS colour mixing experiment

Cardboard disk coloured with the colours of the rainbow on a piece of string
Piece of white cardboard

Rainbow coloured bunting
Single coloured bunting

Several different coloured tennis balls

Microwave
Ruler
Several large chocolate bars
Large plate

Explanation
Explanation: 

(D_ indicates a demonstration)

It’s your best friend’s birthday! Yay! But unfortunately he lives on the other side of the world and you have forgotten to send him his birthday card! Oh no! What’s the quickest way we can transport this birthday card to the other side of the world?
Run? Usain Bolt top speed, 30 mph, would take 35 days! (D1, Run across room)
Racing car? F1 car top speed, 2500 mph, would take 4 days. (D2, Drive RC car across bench)
Helicopter? Top speed, 300 mph, would take 3.5 days. (D3, Fly RC helicopter across room)
Aeroplane? Top speed, 2000 mph, would take 12 hours. (D4, Throw paper aeroplane across room)
Or we could send him an email or speak to him on Skype which would get the message to him almost immediately! But how fast can we send information to the other side of the world and back and how do we send this information so fast?
Using light!
Just like when we use Morse code we can encode a message into a series of on and off flashes of light (D5, Laser beam in smoke machine, flash it on and off).
But what’s the biggest problem in using light to send information around the world? Light travels in straight lines (D5, Laser beam in smoke machine, hold it on) but the earth is a sphere. (D6, Shine torch on sphere, light doesn't go through!). So how can we bend light around the earth? One way to change the direction of light is by using reflection. Just like when we look into a mirror. But it’s not just mirrors that can reflect light. In fact, when light travels through water into air it can be completely reflected back. The surface of the water acts like a mirror (D7, Shine laser into tank of milky water at a shallow angle, see total internal reflection of light at surface of water).
What’s great about this type of reflection is that it applies to any situation where you have water in air, for example for a stream of water (D8, Shine laser into stream of water coming out of a plastic bottle into a bucket, light visible in bucket).
Great thing is that it doesn't just work for water, it works whenever you are travelling at a large angle from something more dense into something less dense. For example through a plastic rod into the air (D9, Shine laser through straight plastic rod and bent plastic rod).
So this is how we can send our Morse code in light around the earth (D9, Shine laser through bent plastic rod while flashing it on and on). We call these optic fibres. Now you may already have these optic fibres in your home, if you have one of these optic fibre lamps (D10, Optic fibre lamp).
Now you can see from this lamp that all sorts of different colours of light can be sent through an optic fibre, so how do we decide which colour of light is best? And where do we get the light from? Where does light come from? The sun, light bulb, laser. Most common source of indoor lighting is a light bulb, so can we use a light bulb to send information down our optic fibre?
Problem with light bulb is that it is made up of several different colours of light. We know this because the light from a light bulb looks white, and when we combine the light from a red, green and blue lamp (three primary colours of light) we get white light (D11, Shine light from red, green and blue lamps onto wall). You can also see this effect when you spin a cardboard disk of the colours of the rainbow very fast (D12, Spin cardboard disk with colours of rainbow on a piece of string very fast).
We can also see that white light is made up of the colours of the rainbow by splitting the colours up using a prism (D13, Shine Maglite light through prism onto white cardboard).
The problem is that it not just prisms that separate out the light into its different colours, this also happens in the optic fibre. So one flash of light gets separated as it travels down the fibre and it takes much longer to receive the message, it delays the message (D14, Bunting, starting with all flags overlapping, while walking from one side of the room to the other, separate out the flags until they are fully separated). Another problem is that the different colours of light are emitted at random directions from the light bulb so it is difficult to get many into the optic fibre (D15, Throw different coloured balls into the air at random, very few will go into the optic fibre).
So how can we overcome this problem? Use a single colour of light. How do we generate a single colour of light? Using a laser. Great thing about laser is that it is a single colour, so it doesn't separate as it travels through the fibre, so the message is not delayed (D14, Bunting, with a single flag walk from one side of the room to the other). Also the light is not emitted at random but in a particular direction so it is easy to get most of the light into the optic fibre (D15, Throw one colour of ball into the air in a particular direction, all will go into the optic fibre).
Great, so now we clearly have light going into the fibre, but how fast can we send a message around the world and back? In order to work this out we need to calculate the speed of light.
Light is part of the electromagnetic spectrum, waves going from gamma rays to radio waves (have slide with radiation symbol, medical x-ray image, visible light, a microwave, a radio alongside waves of increasing wavelength), they all travel at the same speed, so if we find the speed of one, we find the speed of all.
When a microwave is switched on microwaves are generated inside and they form a pattern like this (have slide with animation of standing waves in a microwave). Where there are peaks in the wave, they cook food faster, and where there aren't, the food is cooked slower. This is why microwaves have a spinning bottom, to spread out the heat. But if we remove the spinning plate and put in a large chocolate bar, we should see the chocolate bar melts faster where there are peaks in the wave and slower where there aren't (D16, put chocolate bars on a large plate in microwave for a few seconds, measure the distance between melted patches with a ruler). This tells us the distance between the peaks in the wave. Using this and the frequency written on the back of the microwave (slide with picture of back of microwave) you can calculate the speed of light using this formula, speed of light = frequency x wavelength.
Therefore, speed of light is 3e8 ms-1 and that’s how we can get around the world and back in 0.1344 seconds!

Risk Assessment
Date risk assesment last checked: 
Thu, 12/02/2015
Risk assesment checked by: 
jphr2
Date risk assesment double checked: 
Fri, 13/02/2015
Risk assesment double-checked by: 
Miffles
Risk Assessment: 

D1, Me jogging from one side of room to other
Description:
Me jogging from one side of room to other while carrying a paper envelope.
Risks:
1) Trip hazards
2) Sports injury
Action to be taken to minimise risks:
1) Ensure there are no trip hazards before starting demonstration
2) Jog at a slow pace to avoid a sports injury
Action to be taken in the event of an accident:
1) Call first aider

D2, RC car
Description:
Me driving a remote controlled car across the lecture room bench.
Risks:
1) Electrical hazard
2) Fire hazard
Action to be taken to minimise risks:
1) Ensure car is tested for electrical safety
2) Ensure car is not damaged before starting demonstration
Action to be taken in the event of an accident:
1) Call first aider
2) In the event of a fire, set of fire alarm

D3, RC helicopter
Description:
Me flying a remote controlled helicopter from one side of the room to the other.
Risks:
1) Losing control of the helicopter and hitting audience member or demonstrator
2) Electrical hazard
3) Fire hazard
Action to be taken to minimise risks:
1) Use helicopter with flimsy parts which cannot cause serious injury
2) Ensure I have had training in flying the helicopter
3) Ensure helicopter is tested for electrical safety
4) Ensure helicopter is not damaged before starting demonstration
Action to be taken in the event of an accident:
1) Call first aider
2) In case of fire, set off fire alarm

D4, Paper aeroplane
Description:
Me throwing a paper aeroplane across the room.
Risks:
1) Sharp point of aeroplane going into an audience members or demonstrators eye.
Action to be taken to minimise risks:
1) Ensure aeroplane is not thrown at audience members and that the demonstrator the aeroplane is thrown at is paying attention
Action to be taken in the event of an accident:
1) Call first aider

D5, Laser beam in smoke machine
Description:
Me shining a laser beam at wall through smoke generated by smoke machine
Risks:
1) Eye injury from laser beam
2) Electrical hazard from smoke machine
3) Fire hazard from smoke machine
4) Allergic reaction to smoke
Action to be taken to minimise risks:
1) Use a class ii laser. Ensure that it is never pointed directly at audience members or demonstrators eyes.
2) Ensure smoke machine is tested for electrical safety.
3) Ensure smoke machine is not damaged before starting demonstration.
4) Ensure no audience members or demonstrators are allergic to the smoke before the demonstration.
Action to be taken in the event of an accident:
1) Call first aider
2) In case of fire, set off fire alarm

D6, Torch on globe
Description:
Me shining a torch at inflatable globe
Risks:
1) Electrical hazard
Action to be taken to minimise risks:
1) Ensure torch is not damaged before demonstration
Action to be taken in the event of an accident:
1) Call first aider

D7, Laser in water tank
Description:
Me shining a laser beam into the side of an open tank of milky water
Risks:
1) Eye injury from laser beam
2) Slip hazard from water spillage
3) Crush hazard from falling tank
4) Allergic reaction to milk
5) Electrical hazard from water spillage onto other electrical equipment
Action to be taken to minimise risks:
1) Use class ii laser. Ensure laser beam is not pointed directly at audience members or demonstrators.
2) Ensure water tank is located on a solid bench in a location which minimises the likely hood of spillages.
3) Check whether any audience members are allergic to milk. If so, warn them that the tank contains milk and ensure they do not approach the tank.
4) Ensure the tank is not located near any electrical equipment.
Action to be taken in the event of an accident:
1) Call first aider
2) Wipe up any spills. Turn off electrical equipment near spills.

D8, Laser water stream
Description:
Me shining a laser beam into a stream of water coming out of a plastic bottle into a bucket
Risks:
1) Eye injury from laser beam
2) Slip hazard from water spillage
3) Electrical hazard from water spillage onto other electrical equipment
4) Crush injury from falling bottle
Action to be taken to minimise risks:
1) Use class ii laser. Ensure laser beam is not pointed directly at audience members or demonstrators.
2) Ensure water stream does not spill outside bucket.
3) Ensure water tank is located on a solid bench in a location which minimises the likely hood of spillages.
Action to be taken in the event of an accident:
1) Call first aider
2) Wipe up any spills. Turn off electrical equipment near spills.

D9, Laser rod
Description:
Me shining a laser beam through straight and bent plastic rods
Risks:
1) Eye injury from laser beam
Action to be taken to minimise risks:
1) Use class ii laser. Ensure laser beam is not pointed directly at audience members or demonstrators.
Action to be taken in the event of an accident:
1) Call first aider

D10, Optic fibre lamp
Description:
Optic fibre lamp
Risks:
1) Electrical hazard
Action to be taken to minimise risks:
1) Ensure optic fibre lamp is tested for electrical safety.
2) Ensure optic fibre lamp is not damaged before demonstration.
Action to be taken in the event of an accident:
1) Call a first aider

D11, Coloured lamps
Description:
Shine light from a red, green and blue desk lamp onto a wall.
Risks:
1) Electrical hazard
2) Burn hazard
3) Fire hazard
Action to be taken to minimise risks:
1) Ensure lamps are tested for electrical safety
2) Ensure the lamps are not touched while they are hot
3) Ensure there are no flammable materials near the lamps
Action to be taken in the event of an accident:
1) Call first aider
2) In case of fire, set off fire alarm

D12, Spinning cardboard disk
Description:
Me spinning a cardboard disk attached to the centre of a piece of string
Risks:
1) Strangulation from string
Action to be taken to minimise risks:
1) Ensure children are never left unattended with the string
Action to be taken in the event of an accident:
1) Call first aider

D13, light through prism
Description:
Me shining a torch through a glass prism onto a white piece of cardboard
Risks:
1) Injuries from smashed glass
2) Electrical hazard from torch
Action to be taken to minimise risks:
1) Ensure prism is placed in a location which minimises risk of smashing
2) Ensure torch is checked for damage before demonstration
Action to be taken in the event of an accident:
1) Call first aider
2) Clean up smashed glass

D14, Bunting
Description:
Me walking across room with bunting.
Risks:
1) Trip hazard
2) Strangulation hazard
Action to be taken to minimise risks
1) Ensure there are no trip hazards before starting demonstration
2) Use bunting which breaks before causing injury. Ensure children are never left unattended with the bunting.
Action to be taken in the event of an accident:
1) Call first aider

D15, Tennis balls,
Description:
Me throwing balls around the room and into a large cardboard tube
Risks:
1) Injury from airborne balls
2) Trip hazard from balls
Action to be taken to minimise risks:
1) Ensure balls are not thrown violently at audience members or demonstrators.
2) Ensure balls are picked up directly after ball demonstration.
Action to be taken in the event of an accident:
1) Call first aider

D16, Microwave
Description:
Me placing chocolate bars into a microwave for a few seconds, taking them out and measuring the distance between melted spots with a ruler
Risks:
1) Electrical hazard
2) Radiation hazard
3) Allergic reaction to chocolate
4) Eye injury from ruler
Action to be taken to minimise risks:
1) Ensure microwave is tested for electrical safety
2) Ensure microwave is not damaged before demonstration
3) Check whether any audience members are allergic to chocolate. If so, warn them and ensure they do not approach the demonstration.
4) Do not put ruler near eyes
Action to be taken in the event of an accident:
1) Call first aider

This experiment contains mains electrical parts, see separate risk assessment.
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