Magnetic flux and flux linkage

Q1. Magnetic flux through a surface is defined as Φ = BA. What condition must be met for this equation to hold without any additional trigonometric factor?

Multiple Choice · 1 point

• · The magnetic field must be uniform and parallel to the plane of the surface
• · The magnetic field must be uniform and perpendicular to the plane of the surface
• · The surface must be circular
• · The field lines must be diverging across the surface

Q2. What is the SI unit of magnetic flux?

Multiple Choice · 1 point

• · Tesla (T)
• · Henry (H)
• · Weber (Wb)
• · Tesla metre squared per second (T m² s⁻¹)

Q3. A rectangular coil has N turns and is placed in a uniform magnetic field. Which expression correctly gives the flux linkage through the coil when the field is perpendicular to the plane of the coil?

Multiple Choice · 1 point

• · Φ = BA/N
• · NΦ = NBA
• · NΦ = BA
• · NΦ = NBA²

Q4. A rectangular coil of area 0.04 m² is placed in a uniform magnetic field of flux density 0.5 T with its plane perpendicular to the field. What is the magnetic flux through the coil?

Multiple Choice · 1 point

• · 0.04 Wb
• · 0.01 Wb
• · 0.08 Wb
• · 0.02 Wb

Q5. A 200-turn coil has an area of 0.03 m² and sits in a uniform magnetic field of 0.4 T perpendicular to the coil plane. What is the flux linkage?

Multiple Choice · 1 point

• · 0.012 Wb turns
• · 2.4 Wb turns
• · 24 Wb turns
• · 0.24 Wb turns

Q6. A rectangular coil rotates in a uniform magnetic field. The flux linkage is given by NΦ = BANcosθ, where θ is the angle between the field and the normal to the coil. At what value of θ is the flux linkage at its maximum?

Multiple Choice · 1 point

• · θ = 90°
• · θ = 45°
• · θ = 180°
• · θ = 0°

Q7. Using NΦ = BANcosθ, at what angle θ does the flux linkage through a rotating coil fall to zero?

Multiple Choice · 1 point

• · θ = 0°
• · θ = 45°
• · θ = 90°
• · θ = 180°

Q8. A coil rotates steadily in a uniform magnetic field. At the instant the plane of the coil is parallel to the magnetic field, which of the following is correct?

Multiple Choice · 1 point

• · Flux linkage is maximum and rate of change of flux linkage is zero
• · Flux linkage is zero and rate of change of flux linkage is maximum
• · Both flux linkage and its rate of change are at their maximum
• · Both flux linkage and its rate of change are zero

Q9. A coil of 80 turns and area 0.05 m² rotates in a uniform magnetic field of 0.25 T. What is the maximum possible flux linkage?

Multiple Choice · 1 point

• · 1.0 Wb turns
• · 0.5 Wb turns
• · 2.0 Wb turns
• · 0.25 Wb turns

Q10. Which of the following changes would double the maximum flux linkage through a rotating coil, assuming all other quantities remain constant?

Multiple Choice · 1 point

• · Doubling the angular velocity of the coil
• · Halving the number of turns in the coil
• · Doubling the magnetic flux density
• · Doubling the rate of rotation only

Q11. A coil is rotated from θ = 0° to θ = 90° inside a uniform magnetic field. Which of the following correctly describes the change in flux linkage over this quarter turn?

Multiple Choice · 1 point

• · It increases from zero to its maximum value
• · It remains constant throughout
• · It decreases from its maximum value to zero
• · It decreases then increases back to its original value

Q12. Which of the following correctly explains why flux linkage depends on the number of turns N in a coil?

Multiple Choice · 1 point

• · More turns increase the area of the coil exposed to the field
• · Each turn contributes a flux Φ, so the total flux cut by the coil is NΦ
• · More turns increase the magnetic flux density inside the coil
• · The angle θ changes for each additional turn added

Q13. Put the following stages in order to describe how flux linkage through a coil changes during one complete rotation, starting from the coil normal aligned with the field.

Ordering · 5 points

• 1. Flux linkage is at its maximum value, NΦ = BAN
• 2. Flux linkage decreases as cosθ falls, reaching zero at θ = 90°
• 3. Flux linkage becomes negative, reaching a minimum of −BAN at θ = 180°
• 4. Flux linkage increases back toward zero as θ approaches 270°
• 5. Flux linkage returns to its maximum positive value after a full 360° rotation

Q14. State three factors that affect the magnitude of the flux linkage through a coil and explain how each one affects it.

Long Answer · 3 points

Q15. Explain why the flux linkage through a coil is at its maximum when the coil plane is perpendicular to the magnetic field, but zero when the coil plane is parallel to the field.

Long Answer · 4 points