A-Level Physics Question Analysis Topic: Physics - Galvanometer
Exam Question:
Explain, using a labelled diagram, the principle and working of a moving coil galvanometer. What is the function of (i) uniform radial magnetic field, (ii) soft iron core?
Define the terms (i) current sensitivity and (ii) voltage sensitivity of a galvanometer. Why does increasing the current sensitivity not necessarily increase voltage sensitivity?
Answer:
For A-Level Physics, you should know:
A galvanometer is an electromechanical tool that detects currents in circuits. It is quite sensitive and cannot be used for measuring heavy amounts of current.
The way it works is through the conversion of electrical to mechanical energy. When a current flows in a magnetic field, magnetic torque is felt and rotates through an angle that is proportional to the current that flows trhough it.
Through making uniform radial magnetic fields, magnetic field lines are perpendicular to the galvanometer's magnetic moment.
A soft iron core is used to increase the magnetic field and make the electromechanical field as radial.
Current sensitivity is defined as the deflection produced per unit current flowing in the galvanometer.
On the other hand, voltage sensitivity is the minimum change in a voltage that produces observable change in the galvanometer's output.
As voltage sensitivity decreases as coil's resistance increases, and the effect of an increased number of turns is nullified in this case, there is no change in voltage sensitivity when current sensitivity changes.
The diagram below is for your reference:
Work hard for your A-Level Physics examination!
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