A straight wire carries a current of 850 mA. The wire is at right angles to a magnetic field of flux density 45 mT45\ \text{mT}45 mT.
The force on the wire is 2.0 × 10-3 N.
Use the equation: force=magnetic flux density×current×length\text{force} = \text{magnetic flux density} \times \text{current} \times \text{length}force=magnetic flux density×current×length
Calculate the length of wire in the magnetic field.
Give your answer in cm\text{cm}cm to 2 significant figures.
A student says:
'If I double the length of wire in the field and halve the magnetic flux density, the force on the wire will double.'
Explain whether the student is correct.
The same wire is placed in a different magnetic field of flux density 90 mT90\ \text{mT}90 mT. The length of wire in the field is unchanged.
Calculate the current needed to give the same force of 2.0 × 10-3 N.
Give your answer in mA\text{mA}mA.
48 exam-style questions on OCR GCSE Physics 4.2 Uses of magnetism, covering 4.2.1 The motor effect, 4.2.2 Fleming's left-hand rule, 4.2.3 The force on a current-carrying conductor, 4.2.4 The electric motor, 4.2.5 Electromagnetic induction, 4.2.6 Alternators and dynamos, 4.2.7 How transformers work, 4.2.8 Transformer turns ratio, 4.2.9 Potential differences and turns in transformers, and 4.2.10 Microphones, loudspeakers and headphones. Each one has a worked solution and a mark scheme showing where the marks go.