The Motor Effect

• What is produced around a conducting wire when a current flows through it?

  A magnetic field

  
• How can the shape and direction of the magnetic field around a wire be investigated?

  Using plotting compasses
• What is the pattern of the magnetic field around a current-carrying wire?

  • Made up of concentric circles
  • Indicates no poles
  • Circles get further apart with distance from the wire
  • Strongest closest to the wire

  
• What does the right-hand thumb rule help determine?

  The direction of current flow and the magnetic field around the wire

  
• What happens to the direction of the magnetic field if the current direction is reversed?

  The direction of the magnetic field is reversed
• What occurs if there is no current flowing through a conductor?

  There will be no magnetic field
• How does increasing the amount of current affect the magnetic field?

  It increases the strength of the magnetic field
• What happens to the magnetic field lines when the current increases?

  • The field lines become closer together
  • Indicates a stronger magnetic field

  
• What is the effect of looping a wire into a coil?

  It produces a magnetic field around the coil

  
• Describe the magnetic field around a solenoid.

  • Similar to that of a bar magnet
  • Strong and uniform inside the solenoid
  • One end behaves like the north pole, the other like the south pole
• How can the polarity of each end of a solenoid be determined?

  By viewing it from the end
• What does a clockwise current indicate in terms of solenoid polarity?

  It indicates the south pole

  
• What does an anticlockwise current indicate in terms of solenoid polarity?

  It indicates the north pole

  
• What happens to the poles of a solenoid if the current direction changes?

  The north and south poles will be reversed
• How can the strength of the magnetic field around a solenoid be increased?

  • Increase the size of the current
  • Increase the number of turns in the coil
  • Add an iron core through the center of the coils
• What happens to the iron core when current flows through the coils of a solenoid?

  It becomes an induced magnet
• What is an electromagnet?

  • A solenoid with an iron core
  • The magnetic field can be switched on and off
• What occurs when the current is switched off in an electromagnet?

  There will be no magnetic field produced
• How can the strength of an electromagnet be changed?

  • Increasing the current increases the magnetic field
  • Decreasing the current decreases the magnetic field
• What are some examples of devices that use electromagnets?

  • Scrapyard crane
  • Electric bell
• What happens when the electromagnet in a scrapyard crane is switched on?

  It attracts magnetic materials
• What happens when the electromagnet in a scrapyard crane is switched off?

  It drops the magnetic materials
• How does an electric bell operate?

  • Current passes through the electromagnet, creating a magnetic field
  • The magnetic field attracts the iron armature, causing the hammer to strike the bell
  • The armature movement breaks the circuit, stopping the current and magnetic field
  • The armature returns to its position, re-establishing the circuit
• What is the motor effect?

  It occurs when a wire with current is placed in a magnetic field and experiences a force

  
• What are the factors affecting the force on a current-carrying wire in a magnetic field?

  • Increasing the current increases the force
  • Using stronger magnets increases the force
  • Placing the wire at 90° to the magnetic field lines maximizes the force

  
• What happens if the two magnetic fields are parallel?

  There will be no interaction and no force produced
• What does each variable in the equation F = BIL represent?

  F = force in Newtons, B = magnetic flux density in Tesla, I = current in Amps, L = length in metres

  
• What is the equation to calculate the force on a current-carrying wire?

  F = BIL

  
• What is the maximum force on a current-carrying conductor?

  It occurs when the magnetic field and current are perpendicular
• If a 5 cm length of wire carries a current of 1.5 A and experiences a force of 0.06 N, how do you calculate the magnetic flux density?

  Use the equation: $B =$$\frac{F}{IL}$

  
• What is Fleming's Left-Hand Rule used for?

  • To determine the direction of force, magnetic field, and current
  • All three are perpendicular to each other

  
• How does the direction of the force on a current-carrying wire relate to the current and magnetic field?

  They are all perpendicular to each other

  
• What does Fleming's Left-Hand Rule help visualize?

  The direction of the force, magnetic field, and current

  
• What is the significance of the motor effect in electromagnetic devices?

  • It allows for the conversion of electrical energy into mechanical energy
  • Essential for the operation of motors and other electromagnetic devices
• What should you do with units if they are given otherwise in a worked example?

  Convert them to the correct units, such as cm to m.
• What does Fleming's Left-Hand Rule help determine?

  • The direction of the force (thrust)
  • The direction of the current
  • The direction of the magnetic field
  • All three are perpendicular to each other

  
• How does the direction of the force on a current-carrying wire relate to the current and magnetic field?

  The force is perpendicular to both the current and the magnetic field.

  
• How can you visualize the direction of the force on a wire using Fleming's Left-Hand Rule?

  By using your first finger for the magnetic field, second finger for the current, and thumb for the thrust.

  
• What happens to the coil in a d.c. motor when it is placed in a magnetic field?

  The coil rotates due to the force on it.

  
• What are the components of a simple d.c. motor?

  • A coil of wire that is free to rotate
  • A uniform magnetic field
  • A split ring connected to the circuit
  • Conducting carbon brushes