13 Jul 2026

Magnetic Field of a Solenoid Using a Hall Probe

practical ug-vii electromagnetism solenoid hall-probe

Aim

To determine the magnetic field inside a solenoid and verify its proportionality to current.

Apparatus

Solenoid, regulated current supply, Hall probe, Gauss meter, ammeter, and connecting wires.

Figure

Current through the solenoid produces a field measured by the Hall probe.

Theory

For a long solenoid, the fields of its turns add inside the coil and largely cancel outside. If $n$ is the number of turns per unit length and $I$ is the current,

\[B=\mu_0nI.\]

Therefore a plot of $B$ against $I$ should be linear and its slope gives the field produced per ampere.

Observations

$I$ (A)	$B$ (mT)
0.5	1.0
1.0	2.0
1.5	3.0
2.0	4.0
2.5	5.0

Graph

Magnetic field plotted against solenoid current.

Result

The field-current slope is $2.0\,\text{mT A}^{-1}$, confirming $B\propto I$.

Viva Questions

1. Why is the field nearly uniform inside? Contributions from many turns add symmetrically.
2. Why use a Hall probe? It measures magnetic field without disturbing the coil appreciably.
3. What happens outside a long solenoid? The field is comparatively weak.

Maxima Code

Download the Maxima calculation file.