New
New
Year 11
Edexcel
Foundation

Strength of an electromagnet

I can accurately measure the strength of an electromagnet to analyse how different factors affect it.

New
New
Year 11
Edexcel
Foundation

Strength of an electromagnet

I can accurately measure the strength of an electromagnet to analyse how different factors affect it.

Lesson details

Key learning points

  1. A soft iron core increases the strength of an electromagnet because it becomes magnetised when it is turned on.
  2. The more tightly wound the coil of wire is in an electromagnet, the stronger its magnetic field.
  3. The greater the current through the coil of an electromagnet, the stronger its magnetic field.
  4. The strength of an electromagnet is directly proportional to the current through it.

Keywords

  • Coil of an electromagnet - An insulated wire wound into the shape of a spring.

  • Turn of wire - A single loop of wire in a coil.

  • Soft iron - Very pure iron that cannot be made into a permanent magnet.

  • Directly proportional to - Describes the relationship between two variables, in which doubling the value of one variable doubles the value of the other.

  • Error bars - These show the accuracy of each measurement on a graph.

Common misconception

Digital ammeters are always accurate to the smallest amount they display.

Show pupils a copy of the specifications of the ammeters they are using that show how accurate they really are.

This investigation is a more accurate method for measuring force than the method of counting paper clips an electromagnet can pick up. A useful exercise for some classes is to compare the two methods.
Teacher tip

Equipment

For each group, or for a demonstration: a digital balance, boiling tube, clamp and stand, lab pack, ammeter, connecting wires, single core insulated wire, two crocodile clips and a bar magnet.

Content guidance

  • Risk assessment required - equipment

Supervision

Adult supervision required

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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6 Questions

Q1.
Which of the following types of magnet is the magnetic field of an electromagnet most similar to?
Correct answer: bar magnet
ring magnet
disc magnet
horseshoe magnet
Q2.
A pupil wants to make a strong electromagnet that loses its magnetism completely when switched off. Which of these is a suitable core material? (Note: soft/hard here means magnetically soft/hard.)
copper
Correct answer: soft iron
soft wood
hard iron
steel
Q3.
Which of the following have a magnetic field around them?
a wire that is not carrying a current
Correct answer: a wire that is carrying a current
a positively charged plastic rod
a negatively charged plastic rod
Q4.
How many newtons are equal to a force of 1 mN?
0.0001 N
Correct answer: 0.001 N
0.01 N
1000 N
1 000 000 N
Q5.
Which of the following statements is correct? (Note: assume the objects are on Earth.)
The mass of a 100 g weight is approximately 1 N.
The mass of a 1 kg weight is approximately 1 N.
Correct answer: The weight of a 100 g mass is approximately 1 N.
The weight of a 1 kg mass is approximately 1 N.
Q6.
Two variables, $$a$$ and $$b$$, are directly proportional. Which of the following statements are correct?
Correct answer: If $$a$$ halves, then $$b$$ also halves.
If $$a$$ increases by 5, then $$b$$ also increases by 5.
Correct answer: The point (0, 0) lies on the graph of $$a$$ against $$b$$.
A graph of $$a$$ against $$b$$ is at an angle of 45° to the $$x$$–axis.
Correct answer: A graph of $$a$$ against $$b$$ is a straight line with a positive gradient.

6 Questions

Q1.
When field lines are drawn to represent a magnetic field, which of the following represents a region in which the field is stronger?
field lines that cross
field lines that are farther apart
Correct answer: field lines that are closer together
field lines with more arrowheads drawn on them
field lines with fewer arrowheads drawn on them
Q2.
Which of the following increase the strength of the magnetic field around a coil of wire with a fixed diameter?
Correct answer: adding a steel core
Correct answer: adding a soft iron core
Correct answer: increasing the number of turns in the coil
spreading the turns of the coil further apart
Q3.
If all other variables are kept constant, the strength of an electromagnet is always …
double the current in its coil.
equal to the current in its coil.
independent of the current in its coil.
Correct answer: directly proportional to the current in its coil.
inversely proportional to the current in its coil.
Q4.
An electromagnet’s strength can be investigated using the apparatus shown. When the electromagnet is switched on, there is a positive mass reading on the balance. Which of the following are correct?
An image in a quiz
Correct answer: The electromagnet is exerting a downwards force on the bar magnet.
The electromagnet is exerting an upwards force on the bar magnet.
Correct answer: The electromagnet and bar magnet have like poles facing each other.
The electromagnet and bar magnet have unlike poles facing each other.
Q5.
On a graph of experimental results, lines can be drawn through each point to show the accuracy of the two measurements used to plot it. What is the name of these lines?
Correct answer: error bars
accuracy bars
precision bars
confidence bars
uncertainty bars
Q6.
How many of these graphs show a directly proportional relationship?
An image in a quiz
none of them
Correct answer: 1
2
3
4

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