Two loudspeakers, separated about 1.7 meters emit the same tone of frequency 500 Hz and produce a pattern of constructive and destructive interference.
How it works:
At this frequency, the successive positions of constructive interference (maximum intensities of sound) occur approximately every two meters at a distance of 10 meters (which is roughly the middle of the lecture hall). The separation of maxima would be about 2.3 meters at 440 Hz. One way to make the interference pattern evident to the students is to...
Determine the capacitance of the human body as follows. Charge a person of unkown capacitance to 1000 volts. The person is subsequently connected (in parallel) to an external capacitor of known capacitance. The voltage measured across the capacitor combination allows one to determine the unknown capacitance of the person (typically between 180 — 200 pF).
How it works:
A 1000 volt power supply (output is in the microamp range) is used to put charge on a person. We assume that the amount of charge transferred to the...
What it shows: A mechanical analogy of a wave front consisting of two wheels linked by an axle. It simulates refraction by rolling across a boundary between two surfaces having different rolling friction and thus altered propagation velocities.
Certain materials (sugar in this experiment) are optically active because the molecules themselves have a twist in them. When linearly polarized light passes through an optically active material, its direction of polarization is rotated. The angle of rotation depends on the thickness of the material and the wavelength of the light.
The very first determination of a half-life for a radioactive decay was made by Rutherford. 1 In a study of the properties of thorium emanation, he found that the intensity of the radiations fell off with time in a geometric progression. That historically important result is reproduced in this demonstration experiment. The gas thoron, or thorium emanation, is an isotope of radon (86Rn220) which decays by α emission and has a half life of 55.6 seconds. 2 Using an emanation electroscope, we observe the...
A superconducting material in the presence of a magnetic field excludes that field from its interior. This is shown by levitating a magnet above a high temperature superconductor.
How it works:
We have a 25mm disc of ceramic yttrium barium copper oxide YBa2Cu3O7 that becomes superconducting above liquid nitrogen temperatures (Tc = 90K). Using a cubic neodymium magnet 4mm of side, two effects can be shown. Firstly, the Meissner effect itself, by placing the magnet on the...
A volunteer puts her hands in oil and water in large beakers on thermostated hot plates, at about 60°C. The water beaker hand is removed almost instantly. The oil beaker hand can remain indefinitely.
The heat capacity of oil is about half that of water. Oil is thought of as hotter because it can be heated to higher temperatures than boiling water, but at the same temperature, water moves more heat into your hand than oil does.