This is a question on magnetism. It was not popular question as it was attempted by few candidates due to poor understanding of the concept involved
Part (a) was fairly attempted well by most of the responding candidates.
In part (b) most candidates got it wrong because of wrong application of formula, conversion substitutions and arithmetic.
Part (c) Most candidates shied away from it. The few that attempted it could not explain it satisfactorily.
Part (d). The concept of true bearing was also a mirage to most of the responding candidates.
Candidates wrote W25°N instead of N25° W. Hence the lost marks
Performance generally was below average.
The expected answers are:
- Magnetic line of force
Is an imaginary line in a magnetic field along which a free/isolated north pole would move.
OR
An imaginary line in a magnetic field such that the tangent to it at any point gives the direction of the field at that point
2.When the wire is parallel to the field
- F = /B/ Sin θ
= 4 x 2 x 0.1 x Sin 0° or sin 180°
= 0N
- When the force is maximum
F = |B| Sinθ
= 4 x 2 x 0.1 x Sin 90°
= 0.8N
(iii) When the wire Is at 60* to the field
F = IBl Sin0
= 4 x 2.0 x 0.1 Sin 60°
= 0.693N
3.
Store in pairs with their opposite poles adjacent
Small pieces of soft iron called keepers are placed across their ends
By induction the keepers, become magnets decreasing the reluctance of the air gaps
Both magnets and keepers, form closed loops hence no free poles present, thus preventing demagnetization
- True bearing = 15 + 10 = N25W
