Investigating the magnetic field around a wire
- The magnetic field patterns due to currents in straight wires and in solenoids can be investigated using:
- a thick wire
- a solenoid (a wire wrapped into a coil) - for example, a metal slinky
- cell, ammeter, variable resistor and connecting wires
- cardboard with holes (the holes must be large enough for the wire to fit through)
- clamp stand
- iron filings or a compass
- Spread the iron filings uniformly on the cardboard and place the magnetic needle on the board
- Tap the cardboard slightly and observe the orientation of iron filings
- When the current direction is reversed, the compasses point in the opposite direction showing that the direction of the field reverses when the current reverses
Experiment 1: plotting the magnetic field around a wire
- Attach the thick wire through a hole in the middle of the cardboard and secure it to the clamp stand
- Secure the wire vertically so it sits perpendicularly to the cardboard
- Attach the ends of the wire to a series circuit containing the variable resistor and ammeter on either side of the cell
Using plotting compasses:
- Place plotting compasses on the card and draw dots at each end of the needle once it settles
- Make sure to draw an arrow to show the direction of the field at different points
- Move the compass so that it points away from the new dot, and repeat the process above
- Keep repeating the previous process until there is a chain of dots on the card
- Then remove the compass, or compasses, and link the dots using a smooth curve – this will be the magnetic field line
- Repeat the whole process several times to create several other magnetic field lines
Using iron filings:
- If using iron filings, simply pour the filings onto the cards and gently shake the card until the filings settle in the pattern of the magnetic field around the wire
Experiment 2: plotting the magnetic field around a solenoid
- Attach the thick wire through a hole on one side of the cardboard and loop it through a hole on the other side of the cardboard and secure it to the clamp stand
- Secure the wire so it forms a circular loop around the cardboard
- Attach the ends of the wire to a series circuit containing the variable resistor and ammeter on either side of the cell
Using plotting compasses:
- Follow the procedure outlined in Experiment 1
- Note: this can be carried out using a solenoid, but since a solenoid is essentially many circular loops, the pattern around a circular loop can be extended to give the pattern around a solenoid
Using iron filings:
- Take a solenoid (a metal slinky works well for this) and thread it through pre-made holes in a piece of card
- Pour the filings onto the card and gently shake the card until the filings settle in the pattern of the magnetic field around the solenoid