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Factors affecting the strength of an electromagnet

Extracts from this document...


Ira Gupta

X – B

Physics Lab

Factors affecting the strength of an electromagnet

Introduction: An electromagnet consists of a long coil of wire wound on a soft iron core. When current flows through the wire the soft iron core becomes magnetized by induction and thus acts as a magnet till the current flows. The strength of an electromagnet can be affected by various factors such as no.of coils, specific resistance of the wire used to coil the core, the thickness of the wire etc. In this experiment the effect of changing the no.of coils and the thickness of the wire used will be determined.

Aim: To determine the effect of changing the no.of coils and the thickness of wire used on the strength of an electromagnet.


  • The strength of a magnet will increase with increase in no.of coils as more current passes the iron core causing more efficient magnetic induction and thus a stronger magnetic field.
  • The strength of the magnet will increase with the increase in the thickness of the wire too because it is already known that resistance is inversely proportional to cross-sectional area. Thus as resistance drops, more current will flow through the electromagnet causing a larger magnetic field.


  • Soft iron core  ( a long nail)
  • Copper wire of three thicknesses
  • Power supply
  • Metre rule
  • Connecting wires and alligator clips
  • A magnetic compass
  • Ammeter


  1. Take 80cm of a chosen thickness of copper wire.
  2. Tightly wind it around the soft iron core 40 times. 40 coils should be on the core.
  3. Leave a little wire towards the ends for connections to be made.
  4. Set up the circuit as shown:
  1. Align the electromagnet created north with the help of a compass.
  2. Now place a metre rule parallel to the electromagnet so that the distance from the electromagnet at which the compass deflects may be recorded.
  3. Now switch on the power supply and adjust the current flowing to 0.5amps using the controls on the power supply.
  4. Let the current flow for about thirty seconds.
  5. Then, place the compass, aligned north, on the edge of the metre rule at 100cm and slowly slide it along the meter rule towards the electromagnet.
  6. As it slides, keep a close eye at the distance at which the compass first shows deflection and record the distance observed.
  7. Now reduce the no.of coils to 35 and cut the extra wire keeping only a little at the ends to make connections.
  8. Keep reducing the no.of coils to 30, 25, 20, 15, 10 and recording the distance at which deflection occurs.
  9. Follow the same procedure with different thicknesses of wire.

A modification in procedure:

  • It is known that soft iron magnetizes quickly because its domains are aligned quickly, thus there was a break given between the experiments and the iron bar hammered once gently to remove as much magnetism as possible before carrying on with different no.of coils and thickness.

Safe Test:

  • The un-insulated wire should not be touched when current is flowing.
  • The current should be kept at a safe level and a current overload indicator must be attached to the circuit.
  • The circuit should not be left un-monitored and the power should be switched off as soon as the work is done.
...read more.


The length by which the wire was cut every time the no,of coils was reduced was also kept constant.The electromagnet was realigned every time its position was moved to changed the no of coils.


Raw Data Table

Table 1: Table showing the variation in distance at which the compass deflects with change in no.of coils and diameter of the wire.

No. of Coils

Distance at which compass deflects

Diameter of copper wire
































The only raw data that may be processed is the diameter of the wire to find the cross-sectional area of the wire.         

Processed Data Table

Table 2: Table

...read more.



Graphical Analysis: This graph clearly shows the variation in extent of magnetic field at every thickness for the different no.of coils. The difference in the values of different thicknesses is quite noticeable and also constant.

Conclusion:After close observation and analysis, it can be concluded that as the no.of coils on an electromagnet increase, so does the extent of the field created by it. Also, as the thickness of the wire used for coiling increases the resistance of the wire drops and the electromagnet becomes stronger. The hypothesis stated earlier has been proved right.

Evaluation: Overall, this experiment proved to be quite successful apart from the minor inaccuracies in readings. However, this experiment could have been made better:

  • The experiment could have been carried out more times for a better average.
  • The effect of a larger range of varying thicknesses could have been determined.
  • Two compasses could have been used for measuring the distance at which deflection occurs to take the average distance of both of them.
  • The effect of changing the material of the wire could have also been seen.

...read more.

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