Concepts

Reflection,  plane mirrors, transmission

Overview

A candle appears to be underwater by superimposing the transmitted light from the beaker with the reflected light from a candle. A pane of glass between the candle and the beaker acts as both the transmission medium and the mirror.

This illusion is also known as Pepper's ghost.

Details

Equipment

• [1] Beaker
• [1] Container of water
• [1] Candle
• [1] BBQ lighter or book of matches
• [1] Black fabric
• [1] Desk lamp
• [1] Black metal plate
• [1] White background on a stand
• [1] 2-poled lab stand
• [2] 90-degree clamp
• [1] Pane of glass
• [2] Magnet
• [1] Camera
• [1] Fire extinguisher

Classroom Assembly

1. Attach the 90-degree clamps and magnets to the lab stand to make a holder for the pane of glass. Put the glass in.
2. Place the candle and beaker such that they overlap.
3. Use the metal plate to block the candle from the audience and block stray light sources.
4. Adjust the lighting as desired using the black cloth, white background, and the desk lamp.
5. Focus and zoom the camera on the beaker. Ideally, the field of view doesn't show any edges of the glass.

Important Notes

• Do not place the black fabric anywhere above the candle. The fabric can melt or catch fire.
• Fire is dangerous. Do not run this experiment near anything highly flammable. Be prepared to evacuate, if necessary.
  
• Remember you have a fire extinguisher if an uncontrolled fire starts. Refresh yourself with the fire extinguisher controls, if necessary.

Script

1. Turn off the room lights.
2. Activate the camera.
3. Light the candle.
4. Point out the candle "inside" the beaker.
5. Pour water into the beaker so that the candle appears submerged.
6. Blow out the candle and explain the actual arrangement of the objects in the demonstration. Explain the illusion is sometimes used in stage productions or carnival attractions.

Additional Resources