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Question:

A fuse rated at 0.8 A blows when the switch is closed. If an 80 V supply is supplying power to the circuit, what would be the maximum possible value of the resistance for which the current flows through the circuit?

A 100 ohms
explanation

The fuse is rated at 0.8 A which means that the current will continue flowing through the circuit when the current is limited to 0.8 A. According to ohm's law, \(I = \frac{\mathrm{V} }{\mathrm{R} } \) . First option will give I=80/100=0.8 A which is the rated voltage and the current will flow through the circuit. For second, third and fourth options, currents are I=80/90=0.89, I=80/80=1 A and I=80/70=1.14 A which are greater than the rated current.