Lecture Demos

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DC Series and Parallel light bulbs

DC Series and Parallel light bulbs

Four light bulbs with clips can be wired in series or parallel circuits using two metal rods attached to a 6V battery.

PIRA Code(s): 
5F20.50
Set up time: 
5 minutes
Physics and Science Concepts: 
Parallel and series circuits
Operation: 
First, attach the metal rods to the battery by unscrewing the black caps and place the rods around the screws. Then replace the caps. Next, clip one light bulb on the metal rods to show a circuit with a single light bulb. To show series circuits, clip two bulbs together and place the end of each clip on opposite rods. To show parallel circuits, clip each bulb separately to the rods. The bulbs in series will glow less brightly than the bulbs in parallel.
Safety: 
The ends of the rods pose an eye hazard.

Voltaic Cell

 Voltaic Cell

A voltaic cell is made with copper and zinc electrodes in a sulfuric acid solution.

PIRA Code(s): 
5E40.20
Set up time: 
1 minute
Physics and Science Concepts: 
Electromotive Force and Current
Operation: 
Pour sulfuric acid into the glass container. Wait 5 minutes for the reaction to take place between the dissimilar metals. Place the voltmeter on the overhead and display the voltage generated in the cell.
Safety: 
Be careful around acid. Gloves and goggles should be worn when handling acid.

Series and Parallel Leyden Jars

Series and Parallel  Leyden Jars

Leyden jars are charged by an electrostatic generator connected to the inner electrode while the outer plate is grounded. The inner and outer surfaces of the jar store equal but opposite charges.

PIRA Code(s): 
5C30.40
Set up time: 
5 minutes
Physics and Science Concepts: 
Electricity and Magnetism, Capacitance
Operation: 
Jars can be charged with either the Wimshurst generator (5A50.10) or Van de Graaf generator (5A50.30). Charge Leyden jars in parallel and discharge, charge in parallel again and connect in series before discharging. The intensity of the sparks as well as their duration is much greater for the series connection.
Safety: 
Do not touch the charged capacitor. Make sure the jar is discharged before storing or touching.

Parallel Plate Capacitors

Parallel Plate Capacitors

Two parallel plate capacitors are charged and hooked up to an electroscope. When you change the distance between the plates, the electroscope pointer will move because the potential difference between the two plates changes.

PIRA Code(s): 
5C10.20
Set up time: 
none
Physics and Science Concepts: 
Capacitance
Operation: 
Charge the plates using the Van de Graaff. Disconnect wire going from top of sphere to fixed plate at plate end. Change the spacing of a charged parallel plate capacitor while it is attached to an electroscope. Observe changes in electroscope pointer.
Safety: 
Electroscope can be obtained from demo 5A22.22. The Van de Graaff can be obtained from demo 5A50.30.

Charged Ovoid

 Charged Ovoid

A tear-drop shaped conductor demonstrates that c harges tend to accumulate at sharply curved points. In order to maintain uniform electric potential over a whole conductor, the surface charge density must be greater at sharply curved points.

PIRA Code(s): 
5B30.20
Set up time: 
5 minutes
Physics and Science Concepts: 
Electrostatics, Surface Charge Density
Operation: 
Use the Van der Graaf or Wimshurst generator to charge the ovoid. Touch a proof plane to the pointed end of the ovoid and another to the spherical end. Place the proof planes on the electroscope plate. The deflection will be greater from the proof plane that touched the pointed end.
Safety: 
Electroscope can be obtained from demonstration number 5A22.22.

Van de Graaff Generator

Van de Graaff Generator

The Van de Graaff generator has the ability to produce extremely high voltages when the belt picks up negative charges via friction and transfers them to the sphere. The excess charge accumulates on the outside surface of the sphere.

PIRA Code(s): 
5A50.30
Set up time: 
10 minutes
Physics and Science Concepts: 
Static Electricity, Friction
Operation: 
Plug in the generator. Turn on the rocker switch and adjust speed using potentiometer on the base of the Van de Graaff. Other suggested uses include combining this with other electrostatic demonstrations found under a 5A50 heading. Also, throwing packing peanuts or taping strips of paper to the Van de Graaff are popular demonstrations.
Safety: 
The rod works best on dry days with the blue wig. Care should be taken when operating. Do not approach the generator while it is running. Use the grounding rod to discharge.

Wimshurst Generator

Wimshurst Generator

This is a Wimshurst static electricity generator which can be used to produce large charges for other experiments or may be used directly to view "mini" lightning bolts of +/- 10 cm. Works best in the winter time and on dry days.

PIRA Code(s): 
5A50.10
Set up time: 
2 minutes
Physics and Science Concepts: 
Electrostatics
Operation: 
Place the four (two large, two small) balls on the poles in the front about 1 inch apart. Turn the crank.
Safety: 
Do not touch any metal portions of the generator

Electroscope

Electroscope

The electroscope is used to show electrostatic charge. When a charged rod is brought near the plate, the needle deflects. If you scrape the plate with the rod, it becomes charged and the needle remains deflected. The deflection decreases when you bring an object of opposite charge near the plate.

PIRA Code(s): 
5A22.22
Set up time: 
3 minutes
Physics and Science Concepts: 
Electrostatics
Operation: 
First, show the electroscope in resting stage. Then, charge a rod or other material by rubbing the object in a cloth. Place this near the plate of the electroscope and observe the deflection of the needle. To keep the needle deflected, scrape the plate with the charged object. A decrease in deflection occurs when an oppositely charged object is placed near the plate.
Safety: 
None

Pith Balls

 Pith Balls

A charged PVC or acrylic rod is used to charge the pith balls. The two will repel each other.

PIRA Code(s): 
5A20.20
Set up time: 
1 minute
Physics and Science Concepts: 
Electrostatics, Coulomb’s Law
Operation: 
Charge the rod by rubbing it the through the cloth provide or on your shirt. Hold the rod near a pith ball. The two balls will repel each other. The PVC gives a positive charge and the acrylic rod gives negative charge.
Safety: 
None

Constant Volume Bulb

Constant Volume Bulb

This experiment uses a constant volume thermometer to measure the pressure change with temperature. The Constant Volume Thermometer consists of a sealed steel sphere filled with helium. The pressure of the thermometer is measured first at room temperature, then in boiling water, ice water if desired and finally in liquid nitrogen.

PIRA Code(s): 
4E30.10
Set up time: 
5 minutes
Physics and Science Concepts: 
Gas Laws, Thermodynamics
Operation: 
Fill sphere with water and submerge in buckets of water or liquid nitrogen at different temperatures. Dewar of liquid nitrogen and bucket can be obtained in the physics machine shop.
Safety: 
Always wear protective clothing when handling liquid nitrogen.