Radio Wave Properties

What it shows:

The following is a sequence of experiments that can accompany a standard lecture on electromagnetic waves. The entire sequence is quite long and you may not want to do it all in one lecture.

1) The voltage variation along the length of a dipole transmitting antenna can be made evident. The intensity variation of a fluorescent light bulb, held near the antenna, shows the voltage to be maximum at the ends and minimum in the middle of the dipole.

(2) The radio waves that radiate from the transmitting antenna are detected by a hand-held… Read more about Radio Wave Properties

Fiber Optics

What it shows:

Light is transmitted by a bundle of optical fibers and/or a coiled length of plastic rod, regardless of the twists and turns in the path it must negotiate. Total internal reflection keeps the light confined.

How it works:

A HeNe laser is used as the source of light. The bundle of optical fibers consists of a very large (but unknown) number of individual glass fibers measuring 0.05 mm (0.002") in diameter. About 30 cm of the bundle is exposed at the end while the rest of the length is protected by a rubber sheath.… Read more about Fiber Optics

Tunneling Analog

What it shows:

In quantum mechanics, it is possible for a particle to tunnel through a potential barrier because its wave function has a small but finite value in the classically forbidden region. Here we use FTIR as an optical analog of this quantum mechanical phenomenon.

How it works:

A 45°-90° prism will deflect a beam of light by total internal reflection. When two such prisms are sandwiched back-to-back and pressed together, the air-glass interface can be made to vanish and the beam then propagates onward undisturbed. This… Read more about Tunneling Analog

Gravitational Field Surface

1m diameter rubber sheet acts as curved space for ball bearing masses.

What it shows:

In general relativity, gravity is replaced by a curved space geometry, where the curvature is determined by the presence and distribution of matter. Objects move in straight lines, or along geodesics, but because of the curvature of space, their paths will simulate the effect of gravitational attraction. This demo gives a two dimensional view of warped space.

How it works:

In this 2-D analog, a 1 meter diameter piece of dental dam forms a… Read more about Gravitational Field Surface

The Surface Treatment of Glass

What it shows:

The strength of a material in tension or compression will be affected by discontinuities in its surface structure. This can be demonstrated for glass using microscope slides, and the comparison of failure stress before and after the removal of surface scratches.

How it works:

The slide rests between two custom built test beds (figure 1), the upper bed supporting the load. We use slotted 1kg and 0.5kg masses placed carefully in their holder, and allowing a short time between additions. We find the breaking… Read more about The Surface Treatment of Glass

Limiting Reagent, Vinegar or Baking Soda?

Vinegar and two different amounts of baking soda in plastic soda bottles with balloons.

Two 500ml PETN soda bottles of the same make, split a bottle of vinegar between them.

11" balloons are pre-inflated with dry air, with care taken not to stretch the neck of the balloon. Into the balloons with a funnel go one, two teaspoons of baking soday. With 250 ml of vinegar, that's like six liters of gas potential if one carbon dioxide comes from one acid hydrogen ion.

Tap the baking soda powder down away from the neck of the balloon. Stretch the neck and place it over the top… Read more about Limiting Reagent, Vinegar or Baking Soda?

Pulley Board

Upright board or Blackboard Mechanics with pulley combinations.

pulley board

Special Bouncing Collisions

Same as previous except that mass ratio of balls is 1:3 (softball:basketball) leaving basketball dead and softball four times the height.

tennis and basketball