AQA A Level Physics复习笔记7.9.1 Magnetic Flux

• Electromagnetic induction is when an e.m.f is induced in a closed circuit conductor due to it moving through a magnetic field
  • Examples are a flat coil or a solenoid

   

• This happens when a conductor cuts through magnetic field lines
• The amount of e.m.f induced is determined by the magnetic flux
• The amount of magnetic flux varies as the coil rotates within the field
  • The flux is the total magnetic field that passes through a given area
  • It is a maximum when the magnetic field lines are perpendicular to the plane of the area
  • It is 0 when the magnetic field lines are parallel to the plane of the area

   

• The magnetic flux is defined as:

The product of the magnetic flux density and the cross-sectional area perpendicular to the direction of the magnetic flux density

The magnetic flux is maximum when the magnetic field lines and the area they are travelling through are perpendicular

• In other words, magnetic flux is the number of magnetic field lines through a given area

• Magnetic flux is defined by the symbol Φ (greek letter ‘phi’)
  • It is measured in units of Webers (Wb)

   

• Magnetic flux can be calculated using the equation:

Φ = BA

• Where:
  • Φ = magnetic flux (Wb)
  • B = magnetic flux density (T)
  • A = cross-sectional area (m2)

   

Part (a)

Step 1: Write out the known quantities

Cross-sectional area, A = 40 cm × 73 cm = (40 × 10-2) × (73 × 10-2) = 0.292 m2

Magnetic flux density, B = 1.8 × 10-5 T

Step 2: Write down the equation for magnetic flux

Φ = BA

Step 3: Substitute in values

Φ = (1.8 × 10-5) × 0.292 = 5.256 × 10-6 = 5.3 × 10-6 Wb

Part (b)

The magnetic flux will be at a minimum when the window is opened by 90o and a maximum when fully closed or opened to 180o