Investigate the relationship between the size of the electric current passing through a length of wire and its heating effect?

Answer 1

The relationship between size of current in a wire and its heating effect is very simple :- Heating is proportional to the square of the current. The actual heating depends also on the resistance of the wire. W=I2R ( I is current in Amps, R is resistance in Ohms , W is heat output in Watts. ) (Note: The Watt is strictly unit of power. That is to say the rate that energy is transfered or used at. The Joule is a unit of energy equivalent to roughly the amount of mechanical work done when a 1kg mass is lifted 9.8cm. The Watt is the number of Joules expended per second.) For AC current this relationship gives an instantaneous value for the power. To get the average power you need to use the RMS value. (Peak value divided by the square root of two.) The above relationship holds true for all cases, but the wires resistance will change with temperature. In practice this means the equation must be applied for the wire in thermal equilibrium with it's environment. IE when the rate of heat output equals the rate of energy input. That is, it's working temperature. The way a material changes resistance with temperature can be quite complex and depends on the material, but for metals the resistance increases linearly with temperature. How much is given by the temperature coefficient of electrical resistance for the particular metal. This gives the amount that the resistance changes proportional to the change in temperature as a fraction of the original resistance.

Answer

It's work, not heat, that's proportional to the square of the current passing through a resistance. The amount of heat depends on the temperature difference between the resistance and the surrounding atmosphere.

Answer 2

yes the experiment is to prove Joules law. :)