Question

Eddy currents are used in
(A). Electrolysis
(B). Making a galvanometer dead beat
(C). Electroplating
(D). To increase the sensitivity of galvanometer

Answer 1

Hint: In this case students must think of how eddy currents are produced, which will guide them towards the answer. Eddy currents are currents which circulate in conductors; they are induced by changing magnetic fields.

Complete step by step solution:
When a metallic plate is placed in a changing magnetic field then the flux linked with the conductor changes and it gives rise to an induced current within the plate, according to Faraday’s law of electromagnetic induction. This induced current is known as eddy current. Eddy currents flow in closed loops and they are perpendicular to the direction of the magnetic field. The magnitude of the current is proportional to the strength of the magnetic field, the area of the loop, the flux change linked with the current and it is inversely proportional to the resistivity of the material.

Properties of eddy current:
(a). Eddy currents formed in conductors of non-zero resistivity can produce both heat and electromagnetic forces.
(b). Self-induced eddy currents may produce skin effect in conductors.
(c). Eddy currents may produce resistive forces which are then responsible for the change in energy from one form to another.
The properties of eddy currents are not only limited to these points, but there are several others as well.
Applications of eddy currents:
(i) Electromagnetic Braking
(ii) They are used for magnetic levitation and for producing magnetic effects
(iii) They are used for identification of metals
(iv) They may also be used for vibration and position sensing
In a galvanometer, when the coil oscillates, eddy current is set up in the galvanometer, and because of its property of producing resistive forces, the eddy current opposes further oscillations of the coil of the galvanometer, which in turn enables the coil to attain its equilibrium position almost instantly. As the oscillations of the coil of the galvanometer dies out because of the eddy currents, at that instant, the galvanometer is known as a dead beat galvanometer.
From the above discussions, we can conclude that the answer to the given question is option B. making a galvanometer dead beat.

Note: Students must not be confused with the options making a galvanometer dead beat and increasing the sensitivity of a galvanometer. As discussed in the properties of eddy currents, they have the potential to produce resisting forces and so when produced; they gradually decrease the oscillation of the coil of the galvanometer.