Magnetism and Electromagnetism

• What are the two types of magnetic poles?

  North pole and south pole
• Where are the magnetic forces strongest on a magnet?

  At the poles of the magnet
• What happens when unlike poles of magnets interact?

  They attract each other
• What occurs when like poles of magnets interact?

  They repel each other
• What is the term for the region around a magnet where magnetic forces act?

  Magnetic field
• How does the strength of a magnetic field change with distance from the magnet?

  It is strongest at the poles
• What do permanent magnets do?

  Produce their own magnetic field
• What are induced magnets?

  Magnets that become magnetic in a field
• What happens to induced magnets when removed from a magnetic field?

  They lose their magnetism quickly
• What type of force exists between a permanent magnet and a magnetic material?

  Always one of attraction
• In what direction do the arrows on magnetic field lines point?

  From the north pole to the south pole
• What does the density of magnetic field lines indicate?

  The strength of the magnetic field
• Key Point

  Like poles repel. Unlike poles attract.
• What is flux density in a magnetic field?

  The density of the field lines
• How does the closeness of field lines relate to flux density?

  Closer lines indicate higher flux density
• What is the relationship between flux density and the force felt by another magnet?

  Higher flux density means greater force
• Plotting Fields

  . A magnetic compass contains a small bar magnet

  . The compass needle aligns with the Earth's magnetic field and always points to the magnetic north

  . This provides evidence that the Earth's core must be magnetic

  . A magnetic compass can be used to plot the field around a bar magnet:

  1. Place the bar magnet on a piece of paper

  2. Place the compass at one end of the magnet

  3. On the paper, mark where the point of the compass needle is

  4. Move the compass so the tail of the needle is at the point that has just been marked

  5. On the paper, mark a new point where the needle is

  6. Repeat and connect the marks until the full field is plotted
• What is produced around a wire when current flows through it?

  A magnetic field
• How can the direction of the magnetic field lines be determined?

  Using the right hand grip method
• What does the thumb represent in the right hand grip method?

  The direction of the current
• What do the fingers represent in the right hand grip method?

  The direction of the magnetic field lines
• What factors affect the strength of the magnetic field around a wire?

  The size of the current and distance from the wire
• How can the effect of the magnetic field be observed?

  By using a magnetic compass at different points
• What is a solenoid?

  A wire looped into a cylindrical coil
• How does shaping the wire into a solenoid affect the magnetic field?

  It increases the strength of the magnetic field
• What happens when an iron core is added to a solenoid?

  It creates an electromagnet
• Why does a solenoid increase magnetic field strength?

  It concentrates wire into a smaller area
• How does the looped shape of a solenoid affect the magnetic field lines?

  All field lines are in the same direction
• What shape does the magnetic field around a solenoid resemble?

  That of a bar magnet
• How can the north pole of a solenoid be identified?

  Using the right hand grip method
• What does your thumb point to when using the right hand grip method on a solenoid?

  The north pole of the solenoid
• Electromagnetic Devices

  . Many devices use electromagnets

  . You need to be able to interpret diagrams to determine how they work. For example, here is an electric bell:

  1. When the switch is pushed, the electromagnet is magnetised

  2. The electromagnet attracts the armature

  3. The hammer strikes the gong and breaks the circuit

  4. The armature springs back, completing the circuit again and remagnetising the electromagnet

  5. The cycle repeats for as long as the button remains pushed