Title: Electromagnetism

Hypothesis: The 4 factors which can affect the strength of an electromagnet are the type of

core used, the number of turns of wire, the magnitude of the current used and

the shape of the solenoid.

Aim: To investigate the factors which affect the strength of an electromagnet.

Apparatus: iron nail, horse-shoe nail, copper rod, nickel rod, 100cm length of insulated wire,

connecting wires, 12V power supply, ammeter, rheostat, switch, electronic

balance, iron filings, brush, petri-dishes

Procedure:

1. The circuit was set up as shown above, with the connecting wires wound 50 times

around the iron nail.

2. The switch was turned on. The rheostat was adjusted and the ammeter checked to

ensure that 5 amps of current were flowing through the circuit.

3. The stopwatch was started and the nail placed inside of the petri-dish with the iron

filings. After 30 seconds the switch was turned off and the stopwatch was stopped.

4. A second petri-dish was weighed on the electronic balance and its mass was recorded as

mi.

5. The nail was taken out from the iron filings and placed over the second petri -dish,

allowing the iron filings to fall onto it. A brush was used to brush off any remaining

filings still on the nail.

6. The initial mass of the dish was subtracted from the new mass of the dish mf to obtain

the mass of the iron filings.

7. Steps 2-6 were repeated and an average of the mass of iron filings picked up was

calculated.

8. Steps 2-7 were repeated using a nickel then a copper rod.

9. Keeping all other factors constant, steps 2-7 were repeated using 10 turns around the

iron nail and increasing the no. of turns each time by ten, stopping at 60 turns.

10. Keeping all other factors constant, steps 2-7 were repeated but instead of using 5 amps,

the rheostat was used to adjust the current to 1 amp. The current was increased by 1

amp each time up until 5 amps.

11. Keeping all other factors constant, steps 2-7 were repeated using the iron nail, then

using the horse-shoe nail.

Results:

A. Below: Table 1 showing effect of type of core used

Types of Core Mass Force 1 2 Average

Iron 27 26 26.5 0.265

Nickel 25 25 25.0 0.250 Copper 24 25 24.5 0.245

Shape – rod Variables

Number of Turns – 50 Manipulated – Type of Core

Current – 5A Responding – Mass of Filings

B. Below: Table 2 showing effect of no. of turns

No. of Turns Mass Force

1 2 Average

10 5.0 5.0 5.00 0.500

20 12 9.0 10.5 0.105

30 15 16 15.5 0.155

40 21 19 20.0 0.200 50 26 27 26.5 0.265

60 32 32 32.0 0.320 Type of Core – Iron Variables

Current – 5A Manipulated – No. of Turns

Shape – rod Responding – Mass of Filings

C. Table 3 showing effect of current

Current Mass Force

1 2 Average

1 5.0 5.0 5.00 0.500 2 10 11 10.5 0.105

3 14 16 15.0 0.150 4 21 22 21.5 0.215

5 27 26 26.5 0.265

Shape – rod Variables

Manipulated – Current Number of Turns – 50

Type of Core – Iron Responding – Mass of Filings

D. Table 4 showing effect of shape of an electromagnet

Shape Mass Force 1 2 Average

Rod 26 27 26.5 0.265

Horse-Shoe 27 27 27.0 0.270 Type of Core – Iron Variables

Number of Turns – 50 Manipulated – Shape

Current – 5A Responding – Mass of Filings

Discussion:

An electromagnet is a magnet consisting essentially of a coil of insulated wire wrapped

around a soft iron core that is magnetized only when current flows through the wire.

The type of core used affected the strength of the electromagnet. Based on the results,

iron was shown to be the core which produced the strongest magnetic force, whilst copper

exhibited the least strength.

The results also showed that as the number of turns of coil increased, the strength of

the magnetic force increased. This is because when an solenoid has more turns of wire per unit

length, more fields line up and complement each other, thus producing a larger magnetic

effect. Furthermore, it was shown that increasing current increases the strength of the force of

the electromagnet. This is logical because, an electromagnet only becomes magnetized if a

current is flowing through it, so the larger the current flowing through it, the larger the

magnetic effect should be. The results for the number of turns and current seem to be

somewhat proportional.

Finally, the horse-shoe shaped solenoid exhibited a stronger magnetic force than the

rod shaped one. This is because a horse-shoe is almost a complete loop. Corresponding

magnetic fields on each side of the horse-shoe complement and amplify each other, thus

producing a larger magnetic force.

A clamp & stand could have been used to hold the electromagnet at a fixed distance

from the petri-dish. Therefore, the electromagnet wouldn’t have to be placed in the iron filings.

Also, an iron rod, instead of an iron nail could have been used. This is because a nail is not

completely rod-shaped and this may have affected the results slightly.

Sources of Error:

1. Whilst dropping the iron filings onto the second petri-dish, some may have remained on

the solenoid.

2. There may have been loose connections in the circuit.

3. The power supply may have remained on when making changes to the circuit.

4. The distance between the solenoid and iron filings may have varied for different

recordings.

Precautions:

1. Each time after the current was turned off, the nail was brushed over the petri -dish to

ensure that all the iron filings got into the dish.

2. It was ensured that there were no loose connections in the circuit.

3. Before making any changes to the circuit, it was ensured that the power supply was

switched off first.

4. The electromagnet was dipped inside the iron filings to eliminate the possibility of

varying distances away from the filings.

Conclusion: it was found that all four factors – type of core, no. of turns, current and shape –

affected the strength of an electromagnet.