To investigate experimentally how the resistance of a metallic conductor at constant temperature depends on length and obtain sufficient values to plot a graph of resistance (y-axis) and length (x-axis).
The main variables in a science experiment are the independent variable, the dependent variable and the control variables.
The Independent Variable is what we change or control in the experiment.
The Dependent Variable is what we are testing and will be measured in the experiment.
The Control Variables are what we keep the same during the experiment to make sure it’s a fair test.
In this experiment the:
Remember - these variables are controlled (or kept the same) because to make it a fair test, only 1 variable can be changed, which in this case is the length of wire.
Resistance R =
As the length of wire increases, the resistance will increase.
Justification for the prediction
The greater the length of wire the greater the number of collisions between the free electrons and metal ions.
This will result in greater resistance.
|Water||Electric shock||Do not set up the experiment near taps, sinks etc.|
|Wire gets hot||Minor burns||Do not handle the wire. Switch off between readings.|
1m length of constantan wire, a metre rule, a low voltage power pack, a voltmeter, an ammeter, connecting leads, a switch, 2 crocodile clips, Sellotape.
The temperature of the wire must be kept constant.
Whenever a current flows through a conductor there is a heating effect.
Electrical energy is converted to heat energy.
To ensure the temperature of the wire does not increase, switch off between readings and keep the current as low as possible.
Read the ammeter and voltmeter accurately by reading the scale from directly above the pointer or use digital instruments.
|Length l in cm||Current I in A||Reading 1 (Voltage V)||Reading 2 (Voltage V)||Average (Voltage V)||Resistance R in Ω|