Investigating the Strength of Electromagnets (Oxford AQA IGCSE Combined Science Double Award)

Investigating Electromagnets

Aim of the experiment

•  The aim of this experiment is to investigate the factors that determine the strength of an electromagnet

Equipment

Equipment List

Method

Equipment for investigating the factors that determine the strength of an electromagnet

Experiment 1

Variables

• Independent variable = Current, I

• Dependent variable = Number of paper clips picked up, P

• Control variables:

  • Number of turns, N

Method

1. Set up the circuit, place the variable power supply on zero and close the switch

2. Gradually increase the voltage from the power supply until there is just enough current flowing through the electromagnet for it to hold onto one paper clip. Record the value of the current in the table of results

3. Now increase the current until the electromagnet will just hold two paper clips. The paper clips should be supported end to end and not side by side as shown in the diagram. Record the value of the current in the table of results

4. Repeat these steps until the electromagnet can just hold six paper clips

5. Repeat the entire experiment at least three times

Example Results Table

Analysis of results

An example of a mass-current graph

Experiment 2

Variables

• Independent variable = Number of turns, N

• Dependent variable = Number of paper clips picked up, P

• Control variables:

  • Current, I

Method

1. Wind 50 turns of the copper wire into coils around the iron nail. Leave enough wire at each end to connect to the rest of the circuit

2. Set up the circuit, place the variable power supply on zero and close the switch

3. Secure the nail and coils in the clamp stand

4. Set up the circuit, put the variable power supply on zero and close the switch

5. Gradually increase the voltage from the power supply until there is just enough current flowing through the electromagnet for it to hold onto one paper clip. Record the value of the current in the table of results

6. Now wind 100 turns of the wire onto the nail

7. Adjust the power supply so that the current is the same as before and record the number of paper clips the electromagnet can now support

8. Repeat these steps for 150 and 200 turns

9. Repeat the entire experiment at least three times

Example Results Table

Analysis of results

An example of a mass-number of turns graph

Evaluating the experiment

• Consider any systematic errors or random errors

Systematic errors:

• Make sure the measurements on the ammeter and pan balance are taken at eye level to avoid parallax error (assuming both are scales with needles, this does not apply to digital equipment)

• Ensure both the pan balance and ammeter are zeroed before taking measurements

Random errors:

• The precision of the experiment is improved with the use of a digital ammeter and not an analogue one

• Wait a few seconds for the paper clip to hold after it is added, before turning off the electromagnet

• Make sure the paper clips are added to the same point on the nail each time

Safety considerations

• Make sure that the coil of wire does not get too hot – if it does, switch it off immediately

• Place a mat under the electromagnet to catch any falling paper clips

• Stand up, so it is easier to add the paper clips to the electromagnet