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 val… — Answer & Discussion

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.

A40 ©
B4 ©
C2 ©
D20 ©

Correct answer: D

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CCommunity03 Jul 2021

20 ©

CCommunity11 May 2022

Voltage=V=120V

Current=I=3A

R1=20ohm

R2=?

Solution

Let R=R1+R2

According to ohm law

I=V/R

so

R=V/I

R1+R2=V/I

20ohm+R2=120V/3A

R2=120V/3A-20ohm

R2=40ohm-20ohm

R2=20ohm

CCommunity11 May 2022

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