A student tests whether magnetic force is proportional to current. In both tests the wire is perpendicular to the same uniform field. The table shows the results.
| Test | Current / A\mathrm{A}A | Length in field / cm\mathrm{cm}cm | Force / N\mathrm{N}N |
|---|---|---|---|
| P | 1.0 | 8.0 | 0.040 |
| Q | 2.0 | 4.0 | 0.040 |
The student concludes that force does not depend on current. Which evaluation is correct?
The conclusion is invalid because halving the length offsets doubling the current.
The conclusion is valid because the same magnetic field was used in both tests.
The conclusion is invalid because halving the length should double the force.
The conclusion is valid because equal forces show that current has no effect.