The magnetic field of a current
Answers are for parents and teachers.
1
A long wire carries 15 A. What is B in μT at 3 cm? (μ₀/2π = 2·10⁻⁷ N/A²)
100
2
At 5 cm from a long wire B = 60 μT. What is the current (A)?
15
3
At the centre of a single loop B = μ₀I/(2R). If R is halved and I is doubled, by what factor does B change?
It increases 4 times.
4
Why is the field not zero at the midpoint between two identical parallel currents flowing in opposite directions?
At the midpoint both fields point the same way and add up.
5
Using the screw rule, state the field direction on the left and right sides of a wire with current flowing upwards.
Seen from above the lines run anticlockwise; so, looking at a picture of the wire, the field enters the page on the right side and comes out of the page on the left side.