P.3.7.5.3 Magnetic flux and flux linkage

The diagram shows a long wire placed in a magnetic field directed out of the screen. Which on of these answers correctly describes the direction of the induced current in the wire when it is moved upwards, and to the right?

• Moved upwards: Current to the right

  
  

  Moved to the right: Current to the left

• Moved upwards: No current

  
  

  Moved to the right: Current to the right

• Moved upwards: Current to the right

  
  

  Moved to the right: No current

• Moved upwards: Current to the left

  
  

  Moved to the right: No current

The magnetic flux cutting through a loop of wire is defined as

• area of loop parallel to the field x magnetic field strength

• area of loop perpendicular to the field x magnetic field strength

• length of wire parallel to the field x magnetic field strength

• length of wire perpendicular to the field x magnetic field strength

Magnetic flux is measured in

• teslas

• coulombs

• webers

• farads

A rectangular coil of area A has N turns of wire. The coil is in a uniform magnetic field of flux density B with its plane parallel to the field lines. The coil is then rotated through an angle of 30° about axis PQ. What are the correct initial value and correct final value of the magnetic flux linkage?

• A

• B

• C

• D

The diagram shows a coil placed in a uniform magnetic field. In the position shown, the angle between the normal to the plane of the coil and the magnetic field is π/3 rad.

• A

• B

• C

• D

A 500 turn coil of cross-sectional area 4.0 × 10^–3 m² is placed with its plane perpendicular to a magnetic field of flux density 7.5 × 10^–4 T. What is the value of the flux linkage for this coil?

• 3.0 × 10^–6 Wb turns

• 1.5 × 10^–3 Wb turns

• 0.19 Wb turns

• 94 Wb turns

A bar magnet is pushed into a coil connected to a sensitive ammeter, as shown in the diagram, until it comes to rest inside the coil.

Why does the ammeter briefly show a non-zero reading?

• The magnetic flux linkage in the coil increases then decreases.

• The magnetic flux linkage in the coil increases then becomes constant.

• The magnetic flux linkage in the coil decreases then increases.

• The magnetic flux linkage in the coil decreases then becomes constant.(

A coil of 50 turns has a cross-sectional area of 4.2 × 10^–3 m². It is placed at an angle to a uniform magnetic field of flux density 2.8 × 10^–2 T, as shown in the diagram, so that angle θ = 50°.

What is the change in flux linkage when the coil is rotated anticlockwise until θ = 0°?

• The flux linkage decreases by 2.1 × 10^–3 Wb turns.

• The flux linkage increases by 2.1 × 10^–3 Wb turns.

• The flux linkage decreases by 3.8 × 10^–3 Wb turns.

• The flux linkage increases by 3.8 × 10^–3 Wb turns.

An aircraft, of wing span 60 m, flies horizontally at a speed of 150 m s^–1. If the vertical component of the Earth’s magnetic field in the region of the plane is 1.0 × 10^–5 T, what is the magnitude of the magnetic flux cut by the wings in 10 s?

• 1.0 × 10^–5 Wb

• 1.0 × 10^–4 Wb

• 9.0 × 10^–2 Wb

• 9.0 × 10^–1 Wb

Which line, A to D, gives correct units for both magnetic flux and magnetic flux density?

• A

• B

• C

• D