Magnetism

• What is the definition of a magnetic field?


  area around a magnet where the magnetic force acts
• What are substances that can be permanently magnetised described as?

  magnetically hard
• Give 3 examples of things that are magnetically hard?

  alloys like iron, nickel and cobalt
• Definition of magnetically hard?

  substances that can be permanently magnetised
• Definition of magnetically soft?

  substances that can only be temporarily magnetised
• What are alloys with iron called?

  ferrous
• How to draw a field around a bar magnet?

  increasing in distance between lines

  
• Where do the magnetic field lines always point towards?

  south
• Draw the field around two magnets with unlike poles facing?

  lines must be straight

  
• Draw the field around two bar magnets with like poles facing each other?

  repulsion

  
• How do we set up a uniform magnetic field?

  opposite poles facing, magnets close enough for there to be a field, not too close for there to be attraction
• What do we mean if we say the magnetic field is uniform?

  lines are equal distant away
• How can we make an electromagnetic?

  by putting current through a wire
• What are the positives of electromagnets?


  temporary so can be turned on and off with a switch
• What three ways make a magnet stronger?

  more turns on coil, more current, use an iron core
• What does it mean if the circle in the middle of a wire is shaded in?

  current towards you
• What does it mean if the circle in the middle of a wire has a cross?

  current moves away from you
• What hand rule do we use to decide what way the field goes if given current?

  right hand thumb rule
• How does the right hand thumb rule work?

  depending on centre of wire, point thumb away or towards you and follow knuckle round to nail either anticlockwise or clockwise

  
• How do you draw a field around a solenoid?

  like a bar magnet with north to south

  
• What is the motor effect?

  current moves through coil to make the electromagnetic field, the electromagnetic field interacts with the permanent magnetic field which causes a force which causes movement
• How does the motor work?

  every half turn the split ring commutator reverses the current in the coil
• How can you change the direction of the movement of wire?

  change current direction or polarity of magnet
• What happens to the direction of movement of wire if you change both the current direction and polarity of manet?

  wire moves in original direction
• How would you increase the speed of the wire?

  increase voltage, make wire into coil or make permanent magnetic field stronger
• How does increasing voltage increase the speed of wire?

  makes electromagnetic field stronger which increases interaction between fields so more force
• How does making the wire into a coil increase the speed of wire?

  make the electromagnetic field stronger with increases interaction between fields so more force
• How does making the permanent magnet stronger increase the speed of wire?

  makes electromagnetic field stronger so increases interaction meaning more force
• What might happen if the wire was parallel to the field?

  no interaction so no movement so no force
• State and explain three methods that the induced voltage and current can be increased?

  move the wire quickly which cuts through more magnetic field lines, use stronger magnet so more field lines to cut, wrap wire into a coil so more pieces of wire moving
• What happens during electromagnetic induction if you move the wire?

  it cuts through the magnetic field so a voltage is induced
• What happens during electromagnetic induction if you move the magnet?

  induces a voltage
• What is faraday's law of electromagnetic induction?

  the size of induced voltage across ends of a wire is directly proportional to rate at which the magnetic field lines are being cut
• how to make electricity via induction?

  coil of wire cuts through permanent magnetic field which induces voltage
• How does the AC generator work?

  the rectangular coil spins in magnetic field, as it spins it cuts through field lines, the frequency of alternating current is number of cycles per second
• What does the alternating current mean in a generator?

  the current is the number of complete cycles per second
• Explain the meaning of 50Hz of alternating current?

  current constantly changes direction 50 times back and forth per second
• Explain why there is an alternating current?

  so the current constantly moves back and forth so moves quicker allowing move magnetic field lines to be cut so move voltage is induced
• What happens to voltage if more magnetic field lines are cut?

  more voltage is induced
• How does a loudspeaker work?

  alternating current flows through coil and makes electromagnetic field, this interacts with the permanent magnetic field which cause force so causes movement making a vibration of 100 times per second of a longitudional wave