10. Barrier Penetration

This demonstration uses the microwave apparatus of experiment 2 in the 8D lab. The microwaves produced by a Gunn diode are picked up by a receiver and indicated on a meter visible to the class. When one of the 45 degree prisms is inserted into the beam, the meter reading drops to near zero - the microwaves have been totally internally reflected at right angles. You can demonstrate that this is the case by moving the receiver around to the right-angle position to pick them up. Now the receiver is returned to the original position, and a second prism is brought close to the first as shown above. When the gap is about one centimeter or less, the signal begins to increase - the microwaves have tunneled across the gap into the second prism. When the gap distance is reduced to zero, the signal reaches its full value. As the gap distance is increased, the signal drops off exponentially.

Remember, even electromagnetic microwaves are photons! This is a demonstration of particles penetrating a barrier.