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Unit 9: Magnetism and electromagnets

Investigating electromagnets — HIA International - Grade 7 Revision Notes & Topical Questions

5 min read 8 parts Lesson 5 of 5 3 quizzes

📚 HIA International - Grade 7 Hub / Topical Revision
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Lesson summary

Investigating electromagnets — HIA INTERNATIONAL notes: Identify the factors that affect the strength of an electromagnet and plan fair tests of them.Number of turns — the more turns in the coil, the stronger the electromagnet.Core material — iron and some steels in the core make…

  • Needed to make one
  • Demagnetised
  • Strong electromagnets
  • Independent variable
  • Control variables
  • Line graph

Section 1 of 8Factors that affect strength

Number of turns
  • Number of turns the more turns in the coil, the stronger the electromagnet.
Core material
  • Core material iron and some steels in the core make the strongest electromagnets.
Current
  • Current the greater the current in the coil, the stronger the electromagnet.
Needed to make one
  • Needed to make one a coil of wire, a magnetic core inside the coil and an electric current.
Factor
Factor another word for a variable that will affect something.

Section 2 of 8Ways to increase strength

Ways to increase strength
Increase the number of turns on the coil, keeping the current and core the same.
Use more cells to increase the current, keeping the turns and core the same.
Change the core to soft iron in place of steel, keeping the turns and current the same.
Soft iron
Soft iron iron that is easily magnetised and easily demagnetised.
Demagnetised
Demagnetised having lost its magnetism.
A non-magnetic core such as rubber, wood or aluminium gives a weak electromagnet.

Section 3 of 8Measuring strength

Method
  • Method count how many magnetic objects, such as paper clips, the electromagnet can lift and hold.
Reason
  • Reason strength is measured by the force the electromagnet exerts on a magnetic material.
Strong electromagnets
  • Strong electromagnets scrap-metal cranes need stronger ones than a toaster, and very strong ones use a lot of electricity.

Section 4 of 8Investigating the number of turns

1
Make an electromagnet with an iron nail and five turns of wire, using the cells or power supply setting advised.
2
Switch on and count how many paper clips it holds.
3
Switch off and add five more turns.
4
Switch on again and count the paper clips.
5
Repeat until no more turns fit on the core.
6
Repeat the whole investigation and a third time if any results differ.
Independent variable
  • Independent variable number of turns.
Dependent variable
  • Dependent variable number of paper clips held.
Control variables
  • Control variables current, core and size of paper clips.

Section 5 of 8Investigating the core material

Investigating the core material
Wrap the maximum number of turns around an iron nail and record the paper clips held.
Repeat with other cores of about the same diameter, so the coil need not be unwound.
Repeat each measurement and calculate averages.

Section 6 of 8Recording and displaying results

Table
  • Table record the results and calculate the average for each setting.
Line graph
  • Line graph use for number of turns or current, because they are continuous numbers.
Bar chart
  • Bar chart use for core material, because the materials are separate categories.
Safety
  • Safety keep the electromagnet on for the shortest time, and switch off and tell the teacher if the wire becomes hot.

Section 7 of 8Key terms

TermMeaning
FactorA variable that will affect something.
Soft ironIron that is easily magnetised and easily demagnetised.
DemagnetisedHaving lost its magnetism.
Number of turnsHow many times the wire is wound around the core.
CurrentThe flow of electric charge through the coil.
CoreThe magnetic material inside the coil.
Line graphA graph used when both variables are continuous numbers.
Bar chartA chart used when one variable is made of categories.

Section 8 of 8Exam technique

1
Soft iron is soft like modelling clay — it is iron that is easily magnetised and demagnetised.
2
Any core makes an electromagnet strong — iron and some steels do; rubber, wood and aluminium do not.
3
A line graph is best for core materials — use a bar chart, because the materials are categories.
4
Change several factors at once to save time — change only one factor and keep the others the same.

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