Waves reflecting from two surfaces can interfere constructively and destructively. In this case it is light waves that are being reflected at glass/air and air/glass interfaces. The interference produces a concentric ring pattern of rainbow colors in white light, or dark and light rings in monochromatic light.
As a simulation of atmospheric refraction, this demonstration shows the gradual and continuous bending of light due to a gradient in the optical density of the medium. In this case the variable refracting medium is a tank of sugar water with a vertical gradient in the concentration of sugar and a HeNe laser provides the light beam. It can be used as a model of mirage formation (except that the direction of increasing refractive index is in the opposite direction) or even as a representation of the refraction of seismic waves through the Earth's...
The full spectrum of colors (including white) in a television picture is produced by the additive mixing of only three colors: red, green, and blue.
How it works:
In a color television tube, three separate electron beams are focused so as to strike the appropriate phosphor dot on the screen. By looking at the television screen under considerable magnification, one can clearly see that there are only three phosphors which are stimulated by the electron beam(s). The apparatus is diagrammed below.
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...
When a magnetic field is applied perpendicular to a conductor carrying current, a potential difference is observed between points on opposite sides of the conductor. This happens because the magnetic field deflects the moving electrons (Lorentz force) to the edge of the conductor and the altered charge distribution generates a transverse electric field.
How it works:
The conductor is a small bar (11mm × 2mm × 2mm) of germanium (p-type?). Current (18 mA) is made to flow down the length of the bar by a 3 volt potential...
A rectangular block of copper (measuring 6"×6"×2"), offers VERY little resistance to eddy currents generated by dragging a magnet across its surface. Thus the Lorentz force between the eddy currents and magnetic field is quite strong and you can feel a sizable drag force. Dropping a magnet onto the surface likewise produces a sizable Lorentz force, as evidenced by the damped motion of the magnet's fall. The effects are quite dramatic at liquid nitrogen temperature.
It's impossible to magnetically levitate an object with static magnetic fields. However, it's posible to levitate a magnet with another hand-held magnet by taking advantage of eddy currents.
How it works:
A rectangular block of copper (6"×6"×2") is stacked on top of another one (6"×6"×1"). They are separated by 1" plastic spacers. A rectangular bar magnet (2"×2"×½") is placed in the space between them. When a second magnet is lowered from above, the two magnets attact each other. However, rather than "jumping up"...