P4.3 Electromagnetism

• What phenomenon do electric currents produce?

  Magnetic fields
• How do electric currents produce magnetic fields?

  By flowing through wires and coils
• What is the structure of the magnetic field around a wire carrying current?

  • Concentric circles around the wire
  • Closest together near the wire
  • Strongest magnetic field near the wire
• How can you remember the direction of the magnetic field around a wire?

  Using the right hand rule
• What does the direction of the magnetic field depend on?

  The direction of the electric current
• What does curling your fingers in the right hand rule indicate?

  The direction of the magnetic field
• What direction does the magnetic field go for current flowing upwards?

  Anti-clockwise
• What happens to the magnetic field when current flows in the opposite direction?

  The magnetic field direction reverses
• What occurs when two wires are joined to form a coil with current flowing?

  • Magnetic fields interact
  • Field lines stretch into ellipses
  • A single magnetic field forms through the center
• What is a solenoid?

  A coil of wire with multiple turns
• How does the magnetic field within a solenoid compare to that of a bar magnet?

  It is strong and uniform
• What do the ends of a solenoid represent?

  North and south poles
• What happens to an electromagnet when the current is turned off?

  The magnetic field disappears
• How can you reverse the direction of the magnetic field in an electromagnet?

  By reversing the current direction
• What are the four ways to increase an electromagnet's strength?

  1. Increase the current
  2. Increase the number of turns in the coil
  3. Decrease the length of the coil
  4. Add an iron core
• Why does adding an iron core increase the strength of an electromagnet?

  Iron becomes an induced magnet
• What happens to the iron core when the current is turned off?

  It loses its magnetic field
• What is electromagnetism?

  Electromagnetism is when electrical current flows through a wire, a magnetic field is produced.
• What is the 'right hand thumb rule'?

  It helps determine the direction of current and magnetic field lines.

  
• For a current carrying wire, how could you increase the strength of the magnetic field?

  Increase the current (or voltage).
• For a current carrying wire, how could you change the direction of the magnetic field?


  Change the direction of the current (or voltage).
• What is a solenoid?

  A solenoid is a coil of wire, with a strong uniform magnetic field inside it.

  
• What is an electromagnet?

  An electromagnet is a solenoid with an iron core inside it.

  The magnetic field can be turned on or off by turning the circuit on or off.
• Why do we add soft iron cores to solenoids?

  The iron core increases the strength of the solenoid's magnetic field.
• Give 4 ways to increase the strength of a solenoid.


  1. Increase the current.
  2. Increase the number of turns in the solenoid, while keeping the length the same.
  3. Reduce the length of the solenoid while keeping the number of turns the same.
  4. Add an iron core.
• When an electrical current flows through a material, a magnetic field is always produced
• The right hand rule can tell us the direction of the magnetic field induced by a flowing current.

  In the right hand rule, the thumb is placed following the same direction as the current is travelling, and the fingers are the curled in the direction of the magnetic field lines.
• An electromagnet & A solenoid.

  
• In an electromagnet, a current is required to produce the magnetic field.

  When the current is switched off, the magnetic field:

  Disappears
• Describe the four ways to increase the strength of an electromagnet.


  1. Increase the current.
  2. Increase the number of turns in the solenoid, while keeping the length the same.
  3. Reduce the length of the solenoid while keeping the number of turns the same.
  4. Add a soft iron core.
• A solenoid with an iron core will be much stronger than one without because the magnetic fields from all the loops add together at the centre of the coil. The iron core increases the strength of the magnet even more because it has many small regions called domains that become aligned when the current passes through the wire. This makes the magnetic field very strong.
• Moving a permanent magnet into a solenoid causes the magnetic field inside the solenoid to change. This induces a current in the wire which creates its own magnetic field. When the magnet is removed, the current stops so there is no longer any magnetic field inside the solenoid.