2021 Problem 10

Isaac P Abraham
2020 Dec 25

A galvanometer with a resistance R is used to measure the current from a thermocouple of voltage

E

and internal resistance

r

, where

r<<R

. During a physics experiment, the galvanometer needle went off-scale. A bright physicist recalled the concept of current division and recommended adding a resistor

R

in parallel with the ammeter. Current division should cause half the current to flow in the galvanometer, bringing it back in-scale by some amount. How did the galvanometer respond?

Ref: Valerii Ilyushchenko (translated by V.N. Lange), "Science for everyone", Mir Publishers, Moscow, USSR.