5A10.10 Rods, Fur and Silk

Charge different material rods with felt, silk, plastic etc. and observe with electroscope.

Setup Requirements: Minimal. Black or grey rods are negative when rubbed with fur. Clear rods are positive when rubbed with clear plastic.

Electroscopes can be erratic due to bent pointer and improper balance causing the pointer to stay in vertical position. Suggested activities:

1. Charge up black or gray rods using fur or wool. The rod will be negatively charged. Rub the rod across the disk on top of green electroscope. Remove rod from disk. The needle (pointer) should move away from vertical position. Put the wool or fur on top of the disk. It should discharge the electroscope since they are positive.

2. Charge electroscope as above. Rub clear or milky plastic rod with clear plastic. It will be positive. Bring near negatively charged needle. The needle should be attracted toward the clear rod.

3. For induction use the Braun design that has a cylinder as pointer rather than a needle. Charge up the black or gray rod. Place close to but not touching disk. Touch disk with other hand. Count to 10. Remove hands from vicinity of scope. Cylinder should move away from vertical. If not tap side of electroscope. The cylinder should be positive. Place negatively charged rod near cylinder. It should be attracted.

Equations: None

Safety Issues: None

5A20.10 Rod on Pivot Attracted to Charged Rod

A metal rod on a pivot is attracted to a charged rod. Rod can be positively or negatively charged. Charges in metal rod are separated by electrical force due to charged rod. This produces a net attraction. 

Setup Requirements: Minimal. A medium size (meter stick) and large size (piece of lumber) version are also available.

Equations: None

Safety Issues: None

5A20.15 Electric Force Between Plates

A device is availble to demonstrate the force between charged objects. One metal plate is connected to ground. Another plate connected to a spring is suspended several centimeters above grounded plate. This plate is connected to sphere of Van de Graaff. The plates will acquire opposite charges. The one on spring will move down until it touches other plate and charge is neutalized. The spring will then pull the plates apart.

Setup Requirements: Assembled as needed. At least 1 day notice needed to assemble and test.

Equations: Coulomb's Law and F=qE

Safety Issues: High voltage on Van de Graaff.

Note: The low voltage VDG shown in picture is erratic. Some days it works, some days it does not work. It is no longer sold by company we bought it from. The green VDG voltage is so high there is little difference in time to charge up.

Use the Van de Graaff to illustrate the difference between conductors and insulators. Put aluminun foil on base of one of the devices with red or yellow threads. Put the other one on top of the Van de Graaff and note how long it takes to charge up and threads to stick out. Repeat with the one with foil.

Setup Requirements: Minimal

Equations: None

Safety Issues: High Voltage on VDG

5A40.20 Can attracted to charged rod

An aluminum can is attracted to a charged rod.

Setup Requirements: Minimal

Equations: None

Safety Issues: None

5A50.10 Wimshurst Machine

Produce sparks using a Wimshurst generator. Large and small versions available. Read note about direction to spin. Device seems to demonstrate symmetry breaking.

Setup Requirements: Some adjustment needed.

Equations: None

Safety Issues: High Voltage

5A50.30 Van de Graaff Generator

Show sparks from a Van de Graaff generator to a nearby grounded ball. Demonstrate like charges repel. Put pieces of plastic on top before turning on.

Setup Requirements: Use new green base version instead of one in photograph.

Equations: None

Safety Issues: High Voltage Shock. A stick is available to turn off if you want to avoid shock.