Question Constellation Sign up for free AQA · GCSE · Physics · Higher
Magnetic flux density between the magnets calculation
The length of the wire in the magnetic field between the magnets is 80 mm.
The current in the wire is 4.6 A.
The force on the wire is 0.092 N.
Calculate the magnetic flux density between the magnets. Give the unit.
Write your answer first. You can study the marking guidance whenever you need it.
Study the marking See what earns credit and compare it with a full-mark answer.
Marking points
- 1 Converts 80 mm to 0.080 m and substitutes into F = BIl.
- 2 Rearranges correctly to make B the subject.
- 3 Calculates 0.25.
- 4 Supplies tesla or T in the separate Unit field.
Full-mark answer
Convert the length: l = 80 mm = 0.080 m. Using F = BIl, B = F/(Il) = 0.092/(4.6 × 0.080) = 0.25 T.
Why this answer loses marks
I substituted the wire length in millimetres.
The wire length must be converted to metres before using the motor-effect force equation.