tag:techtv.mit.edu,:Array/185183380 2008-07-11 16:51:41 -0400 MIT Department of Physics Technical Services Group <p>An cathode ray tube (CRT) television is connected to a video camera. When a strong magnet is brought close to the television screen, the image becomes warped and discolored.</p><p>While many new televisions use flat screen technology, older CRTs produced images by firing electron guns (one red, one green, one blue) through the television body onto the back of the screen. When a magnet is brought close to the screen, it deflects the paths of the electron beams and distorts the picture. A strong enough magnetic field can even create a hole in the electron beams, causing a black spot on the picture. </p><p>This TV has been subject to many magnet encounters, which has permanently damaged the picture. </p> 96 tag:techtv.mit.edu,:Array/185127660 2008-07-08 10:38:56 -0400 MIT Department of Physics Technical Services Group <p>Two large coils of wire ("Helmoholz coils") are connected to 125V DC power, and produce a uniform magnetic field between the coils. A separate coil is suspended with this field. Switching the polarity of the DC current in the inner coil causes it to rotate in opposite directions.</p><p>This principle is used by devices called <a href="http://en.wikipedia.org/wiki/Galvanometer">galvanometers</a> to measure electric current. </p> 47 tag:techtv.mit.edu,:Array/185097980 2008-06-26 13:51:08 -0400 MIT Department of Physics Technical Services Group <p>Two flexible wires are suspended vertically. The wires are conected in series or parallel to a 12V storage battery. When the wires are connected in series and power is applied they will repel each other; when they are connected in parallel they weill attract one another.</p><p>This effect is due to the magnetic fields created by the charge flowing through the wires. When the wires are in parallel, the currents in each are going in the same direction and thus attract. In series the currents are going in opposite directions and repel. </p> 50 tag:techtv.mit.edu,:Array/185072760 2008-06-25 16:28:50 -0400 MIT Department of Physics Technical Services Group A magnet with a very strong magnetic field is held in place on an aluminum disk. The disk is attached to a motor powered by variable AC current. When the disk rotates, the magnet will levitate above it due to <a href="http://en.wikipedia.org/wiki/Eddy_currents">eddy currents</a> generated in the disk. With the disk spinning, these eddy currents form to oppose the magnetic field of the magnet, making it levitate. When the motor is turned off, the magnet falls back to the disk. 48 tag:techtv.mit.edu,:Array/185053760 2008-06-26 16:47:33 -0400 MIT Department of Physics Technical Services Group <p>A long length of wire is suspended horizontally between the poles of a magnetron magnet. When a large current from a 12V storage battery is passed through the wire, the wire jumps out of the magnetic field. When the direction of the current is switched, the wire jumps the opposite direction.</p><p>The magnetron magnet in this demonstration was originally used in MIT's groundbreaking research developing radar during and after World War II. Microwave emitting <a href="http://en.wikipedia.org/wiki/Cavity_magnetron">cavity magnetrons</a> need strong magnetic fields, which were often created by powerful permanent magnets like the one used in this demo. </p> 37