What effect does the rotating part of the loop have on the needle of the galvanometer?

The rotating part of the loop in a galvanometer generates a changing magnetic field, which induces an electromotive force (EMF) in the coil according to Faraday's law of electromagnetic induction. This induced EMF causes a current to flow through the galvanometer circuit, resulting in the deflection of the needle. The degree of deflection is proportional to the strength of the current, allowing the galvanometer to measure the current's magnitude. Thus, the rotating loop effectively converts mechanical motion into an electrical signal detectable by the galvanometer.