P.3.7.5.3 Magnetic flux and flux linkage

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 rectangular coil of area A has N turns of wire. The coil is in a uniform magnetic field, as shown in the diagram.

When the coil is rotated at a constant frequency f about its axis XY, an alternating emf of peak value ε₀ is induced in it.

What is the maximum value of the magnetic flux linkage through the coil?

• 
• 
• π f ε₀

• 2π f ε₀

The graph shows how the magnetic flux, Φ, passing through a coil changes with time, t.

Which one of the following graphs could show how the magnitude of the emf, V, induced in the coil varies with t?

• 
• 
• 
• 

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

The graph shows how the magnetic flux passing through a loop of wire changes with time. What feature of the graph represents the magnitude of the emf induced in the coil?

• the area enclosed between the graph line and the time axis

• the area enclosed between the graph line and the magnetic flux axis

• the inverse of the gradient of the graph

• the gradient of the graph

The magnetic flux through a coil of N turns is increased uniformly from zero to a maximum value in a time t. An emf, E, is induced across the coil. What is the maximum value of the magnetic flux through the coil?

• 
• 
• E t N

•