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Two Way Mirror

Introduction
See things appear and vanish through the two way mirror
Useful information
Kit List: 

- mirror table-top (make sure that the tops of the lights are covered)
- mirror perspex sheet
- pins to hold the two bits together
- dark room
(doesn't currently exist)

Explanation
Explanation: 

*** OVERVIEW ***

We have a sheet of perspex, with variable lights on each side that can appear as a mirror or as a glass window, depending on the lighting.

Possible activities:
- Demonstrating when you can see through the mirror and when you can't.
- Demonstrating how sometimes you can only see one way through the mirror.

Other things to talk about:
- Uses of two way mirrors and where we see them in real life - talk about looking through windows at night with the lights on inside.

Tips for demonstrating:
- Don't let children go under the table. Smaller children seem to be tempted to do this, presumably to check what is really on the other side.
- When you talk, remember to speak up because your voice has to carry through the sheet of perspex.

*** KIT LIST ***

- mirror table-top (make sure that the tops of the lights are covered)
- mirror perspex sheet
- pins to hold the two bits together
- dark room

*** OVERVIEW ***

We have a sheet of perspex, with variable lights on each side that can appear as a mirror or as a glass window, depending on the lighting.

Possible activities:
- Demonstrating when you can see through the mirror and when you can't.
- Demonstrating how sometimes you can only see one way through the mirror.

Other things to talk about:
- Uses of two way mirrors and where we see them in real life - talk about looking through windows at night with the lights on inside.

Tips for demonstrating:
- Don't let children go under the table. Smaller children seem to be tempted to do this, presumably to check what is really on the other side.
- When you talk, remember to speak up because your voice has to carry through the sheet of perspex.

*** SETTING UP ***

When setting up ensure that that no light can get from one side to the other without going through the perspex, so tape the plastic walls of the inner dark room to the perspex.

Make sure that no external light gets into each side, i.e. that the "curtains" in the entrance to each side of the perspex block out all the light.

Ensure that the light from each lamp projects only away from the perspex, not upwards or towards the perspex; in the past this has been achieved by covering half the lamp with a cardboard cover wrapped in black tap.

*** BASIC PROCEDURE AND EXPLANATION ***

- Start off with everything dark - and try to get half a group in each end.

- Try to get them to start lighting up one end at a time. Let them have a play - some kids find it fascinating.

- When they a getting bored ask what is happening. Basically 10-20% of the light is reflected and the rest goes through, so if the other side is really dark all you can see is the reflection, and if the other side is bright you will hardly see the reflection.

- The perspex lacks reciprocity: it appears as a mirror to one side but as a window to the other, so you can be seen by the other side but you cannot see them.

- A lot of children fail to realise this. The way to do this is to get them to wave while asking things like "What can you see?" and "But what can you see?", and directing your voice to one side or the other. Then clarify by saying e.g. "So John can see you, but you can't see him".

*** OTHER THINGS TO TALK ABOUT ***

- Try to make the connection with seeing through windows at night vs day (e.g. you have to shade the glass with your hand to see from the light side to the dark side).

- Ask them if they've ever walked down a street at night and seen people in their houses who have forgotten to draw the curtains. Ask if they think the people could see them.

Risk Assessment
Date risk assesment last checked: 
Tue, 08/01/2013
Risk assesment checked by: 
Ophelia
Date risk assesment double checked: 
Sun, 20/01/2013
Risk assesment double-checked by: 
Richard H
Risk Assessment: 
DESCRIPTION Two visitors sit on each side of a safety screen in the dark. Use the dimmer lights to see each other.
RISKS
  • 1. Heavy screen, could fall
  • 2. Hot lights, could burn
  • 3. Electrical hazard
  • ACTION TO BE TAKEN TO MINIMISE RISKS
  • 1. Screen is made to be heavy enough to be sturdy. Ensure catches are secure and that the screen won't fall over.
  • 2. Experiment is designed so the lights are in a plastic enclosure so it shouldn't get too hot. They are a long way away from the users so it is difficult to touch them anyway.
  • 3. All electrics are at 12V. Ensure that power supply has been PAT tested within the last two years.
  • ACTION TO BE TAKEN IN THE EVENT OF AN ACCIDENT
  • Call first aider, and if it is a burn, run under cold water as soon as possible for 10 mins
  • This experiment contains mains electrical parts, see separate risk assessment.
    This experiment is sometimes run in a darkroom, see separate risk assessment.
    Images