SRAMIREZ@9-2004 1

ELECTRICITY AND MAGNETISM Introduction The lecture demonstrations listed in this section also include a short description and outline of how the demonstration experiment works. This is for the benefit of the lecturer (who is going to use it in the classroom) and the student (who will see it demonstrated in class). [To the lecturer: All of the equipment used in these demonstrations is stored in Heldenfels Hall. Some of the equipment is rather delicate and not easily transported to other buildings (our only mode of transport is a cart pushed by hand). When requesting a demonstration, be sure to mention the reference number and name listed in this section (example MEC-1 Friction). Requests for demonstrations to be set up in a different building from Heldenfels will require at least 3 class-days notice. The logistics of setting up demonstrations in different buildings gets difficult without advance notice. Practice with the apparatus prior to use in the classroom is always encouraged.] Contents EM-01 Electrostatic Charge by Friction EM-02 Van De Graff Generator EM-03 Faraday’s Law Demo EM-04 Charge on a Capacitor EM-05 RC Decay Circuit EM-06 Magnetic Field Sources EM-07 Effect of Current on a Compass Needle EM-08 Magnetic Force on Metal Rings EM-09 Magnetic Force on a Current Through a Wire EM-10 Magnetic Force on a Current in a Coil EM-11 Induced EMF in a Coil EM-12 Jumping Ring Apparatus EM-13 Eddy Current Pendula EM-14 Inductance (AC vs DC) EM-15 Magneto-Electric Generator EM-16 Demonstration Motor EM-17 Demonstration Generator

SRAMIREZ@9-2004 2

EM-1 ELECTROSTATIC CHARGE BY FRICTION Equipment: Electroscope PVC tube and cats fur Glass rod and silk cloth Pith balls Comments: Rub the PVC tube with the cats fur and then “slide” the edge of the tube across the top plate of the electroscope, thus putting a negative charge on the plate. Charge the glass rod by rubbing it with the silk cloth and bring the rod (now with a positive charge) close to the plate of the electroscope. Note that the indicating needle of the electroscope will show less of a charge on it. The pith balls may also be used to show the charge on the rod or tube.

SRAMIREZ@9-2004 3

EM-2 VAN DE GRAAFF GENERATOR Equipment: Van de Graaff generator (VDG) Meter stick with pith balls on it Pith balls on stand Whirl on a stand Threads on a stand Comments: CAUTION – The generator can produce high voltages (up to 500 Kv). The sphere (mounted on the same base as the VDG) may be used to ground the charge on the VDG when it is turned off. This will make the VDG safer to touch. To show the charge on the VDG, tape the whirl or the threads apparatus to the top of the VDG. The pith balls may also be brought close to the top of the VDG.

SRAMIREZ@9-2004 4

EM-3 FARADAY’S LAW DEMO

Equipment: Electroscope (Project-o-scope) PVC tube and animal fur Conducting cup on stand Proof plane Comments: Rub the PVC tube with the animal fur and touch the end of the tube to the inside of the metal cup. Take the proof plane and touch the inside of the metal cup Now, with the proof plane, touch the top disk of the electroscope. Do this a few times to verify that there is no charge inside the cup to be transferred to the electroscope. Now, with the proof plane, touch the outside of the cup and then touch the top disk of the electroscope. Do this a few times. What happens to the needle of the electroscope? Does it show a charge present?

SRAMIREZ@9-2004 5

EM-4 CHARGE ON A CAPACITOR Equipment: Electroscope (project-o-scope) Large parallel plate capacitor Overhead projector High Voltage generator and AC adapter Co-axial leads Comments: Place the electroscope on the overhead projector and attach the capacitor to the electroscope. Charge up the capacitor with the HV generator (about 3000 volts) by touching the leads to the sides of the plates. Move the plates of the capacitor closer together and apart and observe the reading on the electroscope. (A dielectric is available)

SRAMIREZ@9-2004 6

EM-5 RC DECAY CIRCUIT Equipment: Overhead projector RC decay apparatus 60 volt HP power supply See-thru meter Leads Comments: Place the RC apparatus on the overhead and connect the power supply to the input jacks (about 20 volts). Make sure the DPDT switch is to the left (toward the input jacks). Now move the switch to the right and watch the meter show the decay of the capacitor through the resistor. The meter should be placed on top of the apparatus so that the needle can be seen on the overhead.

SRAMIREZ@9-2004 7

EM-6 MAGNETIC FIELD SOURCES Equipment: Overhead projector Field sources (assortment) Iron filings 0-8 amp power supply and leads Comments: Place the field sources on the overhead projector. Sprinkle iron filings on top of these sources to display the magnetic fields. Some of the sources may require the power supply to be connected to them.

SRAMIREZ@9-2004 8

EM-7 EFFECT OF CURRENT ON A COMPASS NEEDLE Connect the long wire to the power supply and adjust current to about 8 amps. Hold the wire over the magnetic needle and show how the field of the current in the wire affects the needle. Now loop the wire with a few turns and bring the loop near one end of the magnetic needle. Rotate the loop and bring it close to the same end of the needle. What happens? [Equipment: Compass needle on a holder High current power supply and leads]

SRAMIREZ@9-2004 9

EM-8 MAGNETIC FORCE ON METAL RING (LENZ’S LAW) Equipment: 2 metal rings on a lucite rod attached to a rod and base Bar magnet Comments: One ring is split and the other is solid. Oscillate the bar magnet in and out of the rings to try to cause them to swing.

SRAMIREZ@9-2004 10

EM – 9 MAGNETIC FORCE ON A CURRENT THROUGH A WIRE Equipment: Deflected bar apparatus 0-6 amp power supply and leads Comments: Connect the power supply to the jacks on the deflected bar apparatus. Increase the current to MAX of 6 amps. Note the “bar” deflects (because of the magnetic field of the horse-shoe magnet).

SRAMIREZ@9-2004 11

EM – 10 MAGNETIC FORCE ON A CURRENT IN A COIL Equipment: Coil on mount Bar magnet 0-12 volt power supply and leads Comments: Connect the coil to the battery pack ( 3 volts). Use the bar magnet to cause the coil to swing back and forward. Show the force on the coil due to the magnetic field of the magnet.

SRAMIREZ@9-2004 12

EM-11 INDUCED EMF IN A COIL Faraday’s Experiment of Induction

Equipment: Galvanometer 2 Large coils Bar magnet Battery pack or 6 volt power supply and leads Steel bar (for coupling)

Using a current source- Connect the coil A to the galvanometer and coil B to the battery pack as shown (but leave one lead disconnected to the battery pack). The steel bar should be inserted inside the two coils. “Touch” but do not connect the loose end of the battery pack lead to the terminal of coil B. Note the response of the galvanometer needle. Remove the lead and also note the response on the galvanometer. Any different from the first response? Using a magnet- Separate coil B from coil A. Bring one of the pole ends of a magnet close to the opening of coil A. Quickly insert the magnet into the coil. What is the response on the galv? Quickly remove the magnet. What happens now? Try the other end of the magnet. Try the other opening of the coil. Do we get the same results? Now “slowly” insert the magnet into the coil.

SRAMIREZ@9-2004 13

EM-12 JUMPING RING APPARATUS Equipment: Small jumping ring apparatus 2 rings – one solid and one with a slit in it Coil of wire with a light attached to it Comments: Use the push button on the jumping ring to make the rings jump up in the air or to make the bulb light up.

SRAMIREZ@9-2004 14

EM – 13 EDDY CURRENT PENDULA Equipment: Eddy current apparatus and set of discs 0-6 amp power supply and leads Comments: Attach the discs to the swinging arm of apparatus and set the power supply to MAX of 6 Amps. The disc with the slots should have the least eddy currents induced and the one made of solid copper will have the most eddy currents.

SRAMIREZ@9-2004 15

EM – 14 INDUCTANCE – AC vs DC Equipment: 2 large coils (wired in parallel) Light bulb on base Iron rods wrapped in yellow tape AC/DC voltage output circuit box and leads Comments: Connect the circuit box (DC output) in series with the large coils and light bulb. Insert the iron rod bundle into the center of the coils and note that there is no change in the brightness of the bulb. Now reconnect the circuit to the AC output of the circuit box and again insert the iron rods into the coils. What happens now?

SRAMIREZ@9-2004 16

EM – 15 MAGNETO-ELECTRIC GENERATOR Equipment: “Crank generator” Comments: The crank generator consists of permanent magnets with an armature that rotates as the handle is turned. The turning of the handle on the generator produces current through the neon bulb. The generator should be operated at a slow speed (or the handle will break).

SRAMIREZ@9-2004 17

EM – 16 DEMONSTRATION MOTOR Equipment: Large motor apparatus 3 amp power supply and leads Comments: Connect the power supply [red (black) terminals of motor to the red (black) jacks of the power supply]. Slowly increase the output voltage (MAX 3 AMPS) of the power supply until the motor coils rotate. One may have to pre-set the alignment of the coils of the motor in order for it to rotate.

SRAMIREZ@9-2004 18

EM – 17 DEMONSTRATION GENERATOR Equipment: Large generator apparatus Galvanometer and leads Comments: Connect the generator to the galvanometer. Rotate the spindle of the generator to show that it generates a current as shown on the galvanometer.

SRAMIREZ@9-2004 19