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The magnetic force on a current-carrying conductor
Background
A current-carrying wire or coil can exert a force on a permanent magnet. This is called the motor
effect. The wire could also exert a force on another nearby current-carrying wire or coil.
If the current-carrying wire is placed in a magnetic fi eld (whose lines of force are at right angles to
the wire) then it will experience a force at right angles to both the current direction and the
magnetic fi eld lines.
Source:
https://www.bbc.co.uk/bitesize/guides/zmm39j6/revision/4
Research questions: How does the current affect the magnetic force on a current-carrying
wire?
Equipment
•
Sensitive mass balance
•
Thick copper wire
•
Connecting wires
•
DC power supply
•
Magnets and yoke
Diagram
Method
1.
Place the magnets carefully on either wide of the yoke.
2.
Ensure they are facing each other’s opposite pole.
3.
Zero the balance to ignore the weight of the equipment.
4.
Connect the copper wire to the power pack.
5.
Measure the width of the magnets which will be equivalent to the length of the wire
undergoing the force in the fi eld.
6.
Increase the current to 1.0 A and measure the mass.
7.
Repeat by making the current go in the opposite direction by swapping the terminals. Ignore
the negative sign. This will allow us to obtain an average and an uncertainty.
8.
Obtain at least 5 pairs of values.
Data table
Analysis
The report includes suffi cient relevant quantitative and qualitative raw data that could support a
detailed and valid conclusion to the research question:
complete the data table
Appropriate and suffi cient data processing is carried out with the accuracy required to enable a
conclusion to the research question to be drawn that is fully consistent with the experimental
data:
c
alculate the average mass, force, range and uncertainty.
The report shows evidence of full and appropriate considerations of the impact of measurement
uncertainty on the analysis:
add the uncertainty values to the data table and equipment,
justifying your choice.
The processed data is correctly interpreted so that a completely valid and detailed conclusion to
the research question can be deduced:
d
raw a graph of current against average force,
including error bars.
Calculate the gradient and determine what this is.
Evaluation
A detailed conclusion is described and justifi ed which is entirely relevant to the research question
and fully supported by the data presented.
Write a conclusion, in the form of: as x increases, y
… Explain what mathematical relationship there is between the two variables, ideally in a
linear way. Link this to the gradient. Include max/min lines of best fi t for gradient, x/y
intercepts where appropriate.
A conclusion is correctly described and justifi ed through relevant comparison to the accepted
scientifi c context.
Compare this with the theoretical relationship. What were you expecting to
fi nd? Links these to gradient and x/y intercepts.
Strengths and weaknesses of the investigation, such as limitations and sources of error, are
discussed and provide evidence of a clear understanding of the methodological issues involved in
establishing the conclusion.
What went well, what went less well. Can this be quantifi ed?
The student has discussed realistic and relevant suggestions for the improvement and extension
of the investigation.
What would your next steps be?
Current / A
Mass 1 / g
Mass 2 / g
Average
mass / g
Average
force / N
Range of
force / N
Uncertainty
of force / N
0
1.0
2.0
3.0
4.0
5.0
