Magnetism and induction lab
Explore magnetic fields with magnets and compasses, reverse currents, test the motor effect and induce current by moving a magnet into a coil.
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Learning goals
- Apply Faraday's and Lenz's laws to induced e.m.f. and direction.
- Determine magnetic-field direction with a compass or bar magnet
- Interpret bar-magnet field patterns
- Draw the magnetic field pattern around a bar magnet and between the poles of two bar magnets
- Interpret the field pattern around a straight current-carrying wire
- Draw the magnetic field pattern around a straight current-carrying wire
- Interpret the field pattern around a current-carrying solenoid
- Draw the magnetic field pattern around a current-carrying solenoid
- Relate current magnitude and direction to magnetic field
- Describe experiments showing the force on a current-carrying conductor in a magnetic field
- Describe magnetic force on a charged-particle beam
- Predict force reversal when current or field reverses
- Use Fleming’s left-hand rule
- Deduce that a changing magnetic field can induce an e.m.f.
- Deduce that induced e.m.f. opposes the change producing it
- Deduce factors affecting induced e.m.f. magnitude
A bar magnet. Field lines leave north poles and enter south poles; three plotting compasses line up with the field.
- Current, viewed from magnet
- zero
- Motion
- held still
- Force on 1 m of wire
- 0 mN
- B at compass 1
- 7.02 μT
- Compass 1 from the wire
- 11.4 cm
- B inside the coil
- 0.133 mT
- Induced e.m.f.
- 0 mV
- Current in the meter
- 0 mA
- Magnet speed
- 0.00 m/s
Try this
0 of 5 donePredict each direction, then play Approach, Hold still and Withdraw with the same pole facing the coil. (not done yet)
Approach and withdrawal give opposite currents. Hold gives zero current despite non-zero magnetic flux. Directions are viewed from the magnet’s side; self-inductance is neglected.
Place a compass at a neutral point, where the magnetic fields cancel. (not done yet)
At a neutral point the fields are equal and opposite, so the compass has no field to line up with. Field lines never cross there.
Reverse the current in the straight wire and watch the compasses. (not done yet)
Reversing the current reverses the field. Right-hand grip rule: thumb along the current, fingers curl the way the field goes.
Make the right-hand end of the coil a north pole. (not done yet)
Seen from an end, anticlockwise current makes that end a north pole. More current or more turns make the field stronger.
Push the magnet into the coil fast enough to swing the needle past half-scale. (not done yet)
A current flows only while the field through the coil changes. Moving faster, using a stronger magnet or more turns gives a bigger current; the needle swings the other way when the magnet comes out.
You’ve tried every task.