How does the Mirror Galvanometer work?

Hint: A mirror galvanometer is a type of ammeter that uses the deflection of a light beam to detect the presence of an electric current. The light beam cast onto a scale may be regarded as a long, weightless pointer.

Complete answer:
Working of mirror Galvanometer:
A lamp is placed behind the scale, and its light travels through a hole in the instrument to illuminate the mirror of the galvanometer. When an electric current is sent via the magnet/mirror assembly, the light is reflected back onto the scale.

Mirror galvanometers were employed widely in scientific equipment until efficient, steady electronic amplifiers were developed. The most typical usage were as recording devices for seismometers and subsea cables employed for telegraphy. In current times, the name mirror galvanometer is also used for systems that move laser beams by spinning a mirror via a galvanometer set-up, frequently with a servo-like control loop. The name is commonly shortened as galvo.

This sort of galvanometer is extraordinarily sensitive and can detect extremely faint current flow, such as those that traveled from Canada to Ireland over the first intercontinental cables. As may be seen by moving the current slider backward and forward, the scale reflects the flow of the current. Clerks of the day understood that observations in one direction indicated a dot, but observations in the other way indicated a dash.

Note: The ammeter calculates the total amount of current flowing through a circuit, whereas the galvanometer displays the direction of that current. The ammeter can be used to measure both direct and alternating current, while the galvanometer is only good for measuring direct current.