RP10: Magnetic force on a wire Flashcards
State the safety precautions that should be taken when working with wires carrying high currents.
Wires carrying high currents will get very hot, so you must avoid touching the wire throughout the experiment. The power supply should be turned off when not required, in order to reduce the heating effect.
What rule can be used to determine the force on a current carrying wire in a magnetic field?
Fleming’s left hand rule
Explain how to apply Fleming’s left hand rule.
First finger: direction of magnetic field
Second finger: direction of conventional current flow
Thumb: direction of the force on the wire
What direction do magnetic field lines point in?
Magnetic field lines point from North pole of the magnet to the South pole.
In what direction does conventional current flow?
Conventional current flow is from the positive terminal of the source to the negative terminal.
In this experiment, in what direction is the force on the wire due to the magnetic field?
The force on the wire is upwards, but since the wire is clamped in place, a downwards force will be exerted onto the mass balance.
What device can be added to the circuit to allow the current to be varied?
A rheostat can be added in series into the circuit.
How is the reading from the mass balance converted into a force value?
Force = mass x g
State the equation used to calculate the force on a current carrying wire in a magnetic field.
F = BIL
Describe the graph that should be drawn when plotting the mean mass reading against current.
The graph should be a straight line passing through the origin, since the mass and current should be directly proportional to each other.
How can the magnetic flux density be obtained from a graph of mean mass against current?
The gradient of the graph is m/l and so
B = gradient x (g/L)
where the mass is in kg
What length measurements should be used for calculations?
The length of the magnets (in metres) should be used since this will equal the length of wire that experiences the magnetic field.
What is ignored when considering the length of wire that is experiencing the magnetic field?
The edge effects of the magnets are ignored since in these regions, field strength is low as well as being non uniform. Since it is non-uniform, it would be very difficult to quantify.
What unit is used for magnetic flux density?
Tesla (T)
What type of power source must be used in this experiment?
A direct-current source must be used so that the current, and therefore the force exerted, is constant and in one direction.
