ELECTRICITY EXPERIMENTS

THE PHYSICS SUPERMARKET
  1. Electrostatics
  2. The Chemical Cell
  3. Electron Speed in Wires
  4. Series and Parallel Circuits
  5. Series and Parallel Circuits
  6. Resistance
  1. Resistance and Power Transfer
  2. Power Transfer in Electric Circuits
  3. The Electric Blanket
  4. Internal Resistance
  5. Maximum Power Transfer

1. Electrostatics

In this experiment students investigate the charging of objects by rubbing and then by induction using rods, cloths and an electroscope. They discover there are zero electrical effects inside a closed conducting object.

Polystyrene and ebonite rods, Plastic sheet and woollen cloth, Electroscope, Two conducting spheres on insulating stands, Aluminium foil tied to a nylon line, Hollow conducting metal sphere on insulating stand, Proof plane or small metal object on an insulating handle  Top

2. The Chemical Cell

In this experiment students investigate the transfer of charge when one metal displaces another from a solution. They then try setting up a cell but discover it doesn't work unless the accumulation of charge is overcome with a salt bridge. Current is defined. Students change the chemicals and set up cells which produce different reading on a voltmeter connected to them. The concept of EMF is introduced.

Copper, magnesium and lead strips, Solutions of copper sulfate, magnesium sulfate, sodium chloride and lead nitrate, Paper towel for salt bridge, 0-10 mA milliammeter, 0-12 V DC voltmeter   Top

3. Electron Speed in Wires

This is best done with the teacher leading the exercise. Students do a theoretical analysis of a piece of copper wire and determine the average drift velociy of the electrons through the wire is less than 1 mm per second.

No equipment required  Top

4. Series and Parallel Circuits

Students use two different light globes first connected in series and then in parallel. They measure values for current and potential diffence and discover the circuit laws. Why one globe is brighter in the series circuit and the other is brighter in the parallel circuit is explained.

2-12 V DC power supply, Two 6 V torch globes with different current ratings, Two globe holders, 0-1 A ammeter, 0-12 V voltmeter  Top

5. Resistance

In this experiment, students use a calorimeter heating coil, a ray box globe and a length of thin pencil lead. They measure the current in each for a range of potential differences. Graphs of potential difference versus current are drawn and compared. Resistance is defined and what the shape of each conductor's graph implies about its resistance is discussed. A large current is set up in the pencil lead which causes it to glow and then burn out. Why the lead glows in the centre and why the glowing becomes more concentrated and brighter is related to the shape of the lead after it has burned out.

2-12 V DC power supply, calorimeter, Light/ray box, thin pencil leads, small board with spring clips to hold the leads, Rheostat, 0-5 A ammeter, 0-12 V voltmeter  Top

6. Resistance and Power Transfer

In this experiment students learn to control the brightness of a globe using a rheostat. They connect the rheostat in series with different globes and discover that some can be controlled fully but others can have their brightness varied only a little. They then connect the rheostat in potentiometer mode and learn that it results in full control of the brightness of all the globes. Students measure current and potential difference values and explain why full or partial control was had over each globe.

0-12 V DC power supply, 6 V torch globe and holder, Light/ray box, 0-5 A ammeter, 0-12 V voltmeter, Rheostat  Top

7. Power Transfer in Electric Circuits

In this experiment students measure the time for water to boil in an electric jug. They calculate the size of the resistance of the jug's heating coil and check their calculation with a direct measurement. The concept of the kWh is introduced and students learn how to calculate the cost of operating an appliance.

Electric jug and stop watch, 1 L beaker, Multimeter   Top

8. The Electric Blanket

Students investigate the wiring of a three heat setting electric blanket. They learn how two identical wires can be connected in series to produce the low setting and be connected in parallel to produce the high setting. Old electric blankets with the controller dismantled are required.

Electric blanket with 3 heat settings, Multimeter  Top

9. Internal Resistance

In this experiment students discover that a cell behaves as if it has resistance inside it. They use new and old cells and determine the internal resistance and EMF of each.

1.5 V Dry cell, Rheostat, 0-5 A ammeter, 0-5 V voltmeter, connecting leads   Top

10.Maximum Power Transfer

In this exercise students calculate the power transfer when a cell with internal resistance is conneted to a load with a variable resistance. They discover that the maximum power transfer occurs in the load when its resistance is the same as the internal resistance of the cell.

No equipment needed  Top