A student investigates magnetic fields and electromagnetism.
She hangs a vertical steel horseshoe magnet from a stand and introduces small steel sewing pins to the poles. The diagram below shows the magnet and the pins after she is finished.
Explain why Pin B is attached to Pin A.
State a conclusion that can be drawn from this demonstration about the magnetic field of the horseshoe magnet.
The student repeats the demonstration using soft iron pins instead of steel pins. State one difference she would observe when the pins are removed from the magnet.
The student then investigates an electromagnet made by winding an insulated copper wire around a solid iron nail. She wants to test the following prediction:
"The magnetic strength of an electromagnet increases as the electric current flowing through its coil increases."
Explain which variable is the independent variable in this investigation.
Name two control variables in this investigation.
Describe an experimental method that the student could use to perform this investigation. You should include a description of the circuit diagram she must construct.
