○ Wire to suspend
○ Two stands with clamps
○ Two identical magnets
○ Weighing scales
○ Variable power supply ○ Ruler
○ Set up the apparatus as shown in the diagrams. ○ With no current flowing, tare the balance.
○ Adjust the voltage of the supply so that the current I as measured by the ammeter is 0.50A. Read and record the mass m displayed on the balance.
○ Increase the voltage such that the current increases by 0.50A and repeat this, increasing the current by 0.50A each time up to 6.00A.
○ Repeat the experiment twice more and find and record the mean m for each I.
○ Measure and record the length L of the magnets (i.e. the length of the wire in the magnetic field).
Graphs and calculations
○ Calculate the force F by converting each m into kilograms and multiplying by 9.81 and then tabulate this.
○ Plot a graph of F against I and draw a line of best fit. The magnetic field strength B will be the gradient divided by L.
○ F= BIL ⇒ B = F/IL = G/L where G is the gradient.
○ High currents will flow so do not touch the wire because it will get warm and could cause burns.
Improvements and notes:
○ A variable resistor can be added in series with the wire to make it easier to get the desired currents.
○ Scales with a very high resolution should be used because the forces are generally very small.