D.2 · IB Physics
Magnetic field of a wire and a solenoid
Switch between a long straight wire (seen end-on) and a solenoid (cut along its axis), change the current and the turns per metre, and drag the probe to read the field strength and direction.
Try this
- Wire: set I = 4.0 A and read B at r = 2.0 cm, then at 4.0 cm. Check that doubling r halves B.
- Solenoid: double n at fixed current and confirm B inside doubles; then drag the probe outside and to an end to compare.
- Before pressing Reverse current, use the right-hand grip rule to predict the new field direction and which end of the solenoid becomes the N pole.
Exam tip: for a long solenoid B = μ₀nI depends only on turns per unit length, so convert a total number of turns N and length L into n = N/L before substituting.