When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?

The deflection of a magnetic needle when the free ends of a tester are dipped into a solution can be attributed to the presence of an electric current in the solution. This phenomenon is known as electrolysis.

When the tester's free ends are immersed in a solution, such as an electrolyte, and a potential difference is applied across them (for example, by connecting them to a battery or power source), an electric current starts to flow through the solution. This current is carried by ions, which are electrically charged particles present in the electrolyte.

The flow of electric current through the solution generates a magnetic field around the current-carrying path. This magnetic field interacts with the Earth's magnetic field, causing the magnetic needle to deflect.

The direction of the deflection depends on the direction of the electric current flowing through the solution. According to the right-hand rule for magnetic fields, if you curl your right hand around the current-carrying path with your thumb pointing in the direction of the current, your fingers will wrap around in the direction of the magnetic field lines. As a result, the magnetic needle aligns itself with the magnetic field and shows deflection.

It's worth noting that the deflection observed in this setup is usually quite small and may vary depending on the strength of the current, the concentration of ions in the solution, and the sensitivity of the magnetic needle.