Physics paper 2

• Permanent magnet


  Always has a magnetic field
• Induced magnet


  Material that becomes a magnet when placed in a magnetic field
• Magnetic materials


  • Iron
  • Steel
  • Cobalt
  • Nickel
• Magnetic materials


  • Can be made into a permanent or induced magnet
• Magnetic field


  A region around a magnet where a force acts on another magnet or on a magnetic material
• Strength of the magnetic field

  Depends on the distance from the magnet
• The magnetic field is strongest at the poles of the magnet
• Steps to plot magnetic field

  1. Place compass near the north pole of the bar magnet

  2. Draw cross at north pole of the compass

  3. Move the compass so the south pole of the compass is on the cross

  4. Draw another cross at the north pole of the compass

  5. Continue until we have plotted a complete magnetic field line

  6. Connect all the dots with a line

  7. Use an arrow to show direction of the field line
• The Earth's magnetic field is due to its core
• When current flows through a conducting wire


  A magnetic field is produced around the wire
• A larger current


  Will produce a stronger magnetic field
• The direction of conventional current has been reversed


  The magnetic field compass would deflect
• To increase the strength of a magnetic field

  1. You can coil the wire

  2. The shape is called a solenoid
• When current is turned on, we get a strong & uniform magnetic field inside the solenoid
• 13 ways to increase the strength of the magnetic field produced by a solenoid

  • Increase size of the current
  • Increase number of turns of the coil
  • Placing a piece of iron inside the solenoid (iron core)
• Electromagnets


  • We can change the strength of the magnetic field by changing the size of the current
  • You can turn an electromagnet on or off
• Momentum


  The property that moving objects have, which depends on their mass and velocity
• Momentum is a property that all moving objects have
• Momentum


  • The greater the mass of an object, or the greater its velocity, the more momentum the object has
  • Momentum is a vector quantity - it has size and direction
• In a closed system, the total momentum before an event (e.g. a collision) is the same as after the event. This is called conservation of momentum.
• Conservation of momentum means that no external forces act on the system
• Conservation of momentum in snooker

  • Before: The red ball is stationary, so it has zero momentum. The white ball is moving with a velocity v, so has a momentum of p = mv.
  • After: The white ball continues moving, but at a much smaller velocity (and so a much smaller momentum). The combined momentum of the red and white ball is equal to the original momentum of the white ball, mv.
• Conservation of momentum in a car collision

  • Before: The momentum was equal to mass of moving car x its velocity.
  • After: The mass of the moving object has increased, but its momentum is equal to the momentum before the collision. So an increase in mass causes a decrease in velocity.
• If the momentum before an event is zero, then the momentum after will also be zero. E.g. in an explosion, the momentum before is zero. After the explosion, the pieces fly off in different directions, so that the total momentum cancels out to zero.
• Momentum is always conserved in a closed system
• Calculating momentum


  • The momentum of a 60 kg woman running at 3 m/s is 180 kg m/s