cameroon gce intermediate level 2025 electrical machines 2

SECTION A: MAGNETISM AND ELECTROMAGNETISM

1. a) Define the following terms:

• i) magnetic force (2 marks)
• ii) magnetic field (2 marks)
• b) Give two properties of a magnet (2 marks)
• c) A coil of 150 turns is linked with a flux of 10mWb when carrying a current of 10A.
  • i) Calculate the inductance of the coil (2 marks)
  • ii) If a second coil of 100 turns is uniformly wound over the first coil, what will be the mutual inductance between the coils? (2 marks)

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2. An iron ring has a mean circumference of 50cm and a uniform cross sectional area of 5cm$^2$, at a relative permeability of 2200, the flux density is 1.5Wb/m$^2$. Calculate:

• a) the reluctance of the coil. (5 marks)
• b) the magnetomotive force. (5 marks)

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3.

• a) Figure 1 shows a flat coil of N number of turns carrying a current I. If N=20 and R=2cm, calculate the flux density Bo, and the magnetic field strength H. (5 marks)
• b) Figure 2 shows two straight conductors placed in a magnetic field, carrying currents I$_1$ = 15A and I$_2$ = 10A in the opposite direction and are separated by a distance of d=10cm from one another.
  • Calculate the force exerted on one of the conductors. (5 marks)