Introduction
Following in Hans Christian Oersted’s footsteps, I will start with demonstrating the relationship between electricity and magnetism. By setting up a compass through a wire carrying an electric current, I will show that moving electrons can create a magnetic field.
Objective
I would like to answer the following questions:
- What happens to a compass when a wire is connected to a battery?
- What happens to the compass when you change the direction of the electric current?
- How does the compass needle move when the compass is below the wire? Above the wire?
Materials
- Pocket compass
- One-foot (30 cm) length of fairly thick wire, insulated or bare
- I needed to strip the ends of mine, in order to connect to the battery.
- 1.5 volt electric cell ("battery") of size "D"
- Sheet of paper (5 x 10 cm)
Procedure
- Lay the compass on a table, face upwards. Wait until it points north.
- Lay the middle of the wire above the compass needle, also in the north-south direction. You may lightly tape the wire to the table so that it stays put.
- Connect one end of the wire to each end of the battery. Observe the compass. Did the needle move?
- Yes, the needle moved! When I connected the wires to the battery,
the compass needle (initially pointing North) quickly turned and began
to face East. More specifically, it turned to face the direction
perpendicular to the wire crossing the compass. The wire also quickly
heated up. - Quickly disconnect the wire from the battery (it is not good for the battery to draw such a large current). What happens to the needle when you disconnect the wire?
- The needle slowly returned to face its original orientation (North), and the wire cooled
down. - Repeat with the connections of the battery reversed. In what direction does the needle move this time?
- Similarly to last time, the needle moved to point away from North. However, this time
it turned to the West, stopping when it became perpendicular to the wire crossing the
compass! The wire also heated up. - Take the piece of paper and fold the longer side into pleats (like a little accordion), about 1 cm high. Put the wire on the table, its middle in the North-South direction, put the pleated paper above it so that the wire is below one of the pleats, and place the compass on top of the pleats.
- You can now repeat the experiment with the compass above the wire. What direction does the compass move in this time?
- This time, after connecting the battery to the wire the same way as the first trial,
the compass needle spun to the West (last time, it was to the East)! Like all cases,
the needle stopped turning when it became perpendicular to the wire underneath
the compass. The wire also heated up, then cooled down when the connection was
dropped.
- When the battery's connections were reversed, the needle did the opposite of the
previous corresponding trial. It spun to the East (last time, it was to the West)!
Again, the needle stopped turning when it became perpendicular to the wire
underneath the compass. The wire also heated up, then cooled down when the
connection was dropped.
Analysis
- What happens to a compass when a wire is connected to a battery?
- The compass forgets the magnetic field it originally had detected in favour of the
closer, stronger field generated by the battery/wire combination. Depending on
the location of the wire (relative to the compass) and the direction of current,
the needle will turn to face different directions perpendicular to the wire. - What happens to the compass when you change the direction of the electric current?
- When the direction of the current is changed, without altering anything else, the
compass needle will turn to face the opposite direction of how it
originally turned (when affected by the wire).
- How does the compass needle move when the compass is below the wire? Above the wire?
- When the location of the wire is changed, without altering anything else,
the compass needle will also turn to face the opposite direction of how it originally
turned (when affected by the wire).