• A current-carrying conductor produces its own?magnetic field
  • When interacting with an external magnetic field, it will experience a?force

   

• A current-carrying conductor (eg. a wire) will experience the?maximum?magnetic force if the current through it is?perpendicular?to the direction of the magnetic field lines
  • It experiences no force if it is parallel to magnetic field lines

• A simple situation would be a copper rod placed within a uniform magnetic field
• When current is passed through the copper rod, it experiences a?force?which makes it accelerate

A copper rod moves within a magnetic field when current is passed through it

• The strength of a?magnetic field?is known as the?magnetic flux density, B
  • This is also known as the magnetic field strength
  • It is measured in units of?Tesla (T)

   

• The force?F?on a conductor carrying current?I?at right angles to a magnetic field with flux density?B?is defined by the equation

F = BIL sinθ

• Where:
  • F = force on a current carrying conductor in a B field (N)
  • B = magnetic flux density of external B field (T)
  • I = current in the conductor (A)
  • L = length of the conductor (m)
  • θ = angle between the conductor and external B field (degrees)

   

• This equation shows that the greater the current or the magnetic field strength, the greater the force on the conductor
• The length of the conductor,?L?in this equation is only the length that is?within?the field

Magnitude of the force on a current carrying conductor depends on the angle of the conductor to the external B field

• The?maximum?force occurs when sin θ = 1
  • This means θ = 90o?and the conductor is?perpendicular?to the B field
  • This equation for the magnetic force now becomes:

   

F = BIL

• The?minimum?force (0) is when sin θ = 0
  • This means θ = 0o?and the conductor is?parallel?to the B field

   

• It is important to note that a current-carrying conductor will experience?no?force if the current in the conductor is parallel to the field
  • This is because the?F,?B?and?I?must be?perpendicular?to each other

   

Step 1:?Write down the known quantities

• • Magnetic flux density, B = 80 mT = 80 × 10-3?T
  • Current, I = 0.87 A
  • Length of wire, L = 1.4 m
  • Angle between the wire and the magnetic field, θ = 30o

Step 2:?Write down the equation for force on a current-carrying conductor

F = BIL sinθ

Step 3:?Substitute in values and calculate

F = (80 × 10-3) × (0.87) × (1.4) × sin(30) = 0.04872 = 0.049 N (2 s.f)