Starter quiz
- Which of the following types of magnet is the magnetic field of an electromagnet most similar to?
- bar magnet ✓
- ring magnet
- disc magnet
- horseshoe magnet
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- 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
- soft iron ✓
- soft wood
- hard iron
- steel
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- Which of the following have a magnetic field around them?
- a wire that is not carrying a current
- a wire that is carrying a current ✓
- a positively charged plastic rod
- a negatively charged plastic rod
-
- How many newtons are equal to a force of 1 mN?
- 0.0001 N
- 0.001 N ✓
- 0.01 N
- 1000 N
- 1 000 000 N
-
- 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.
- The weight of a 100 g mass is approximately 1 N. ✓
- The weight of a 1 kg mass is approximately 1 N.
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- Two variables, and , are directly proportional. Which of the following statements are correct?
- If halves, then also halves. ✓
- If increases by 5, then also increases by 5.
- The point (0, 0) lies on the graph of against . ✓
- A graph of against is at an angle of 45° to the –axis.
- A graph of against is a straight line with a positive gradient. ✓
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Exit quiz
- 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
- field lines that are closer together ✓
- field lines with more arrowheads drawn on them
- field lines with fewer arrowheads drawn on them
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- Which of the following increase the strength of the magnetic field around a coil of wire with a fixed diameter?
- adding a steel core ✓
- adding a soft iron core ✓
- increasing the number of turns in the coil ✓
- spreading the turns of the coil further apart
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- 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.
- directly proportional to the current in its coil. ✓
- inversely proportional to the current in its coil.
-
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?- The electromagnet is exerting a downwards force on the bar magnet. ✓
- The electromagnet is exerting an upwards force on the bar magnet.
- The electromagnet and bar magnet have like poles facing each other. ✓
- The electromagnet and bar magnet have unlike poles facing each other.
-
- 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?
- error bars ✓
- accuracy bars
- precision bars
- confidence bars
- uncertainty bars
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How many of these graphs show a directly proportional relationship?- none of them
- 1 ✓
- 2
- 3
- 4
-
Worksheet
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Presentation
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Video
Lesson Details
Key learning points
- A soft iron core increases the strength of an electromagnet because it becomes magnetised when it is turned on.
- The more tightly wound the coil of wire is in an electromagnet, the stronger its magnetic field.
- The greater the current through the coil of an electromagnet, the stronger its magnetic field.
- The strength of an electromagnet is directly proportional to the current through it.
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.
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.
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