Question

A 120 v lamp-dimming circuit is controlled by a rheostat and protected from excessive current by a 3 a fuse. To what minimum resistance value can the rheostat be set without blowing the fuse? Assume a lamp resistance of 20 ohms.

a. 40

Answer 1

Given in the question :-

R₂ = 20 Ω

V = 120

I = 3 A

Refer to the attachment .

Now , We know the formula.

v = I × R

R = V/I

R₁ + R₂ = V/I

R₁ + R₂ = 120/3

R₁ + 20 = 40

R₁ = 20 Ω

Hence the minimum resistance is 20 Ω.

Hope it Helps :-)