# Electric circuit problem, finding internal resistance

1. A battery whose emf is 6.0 V is connected to a 2.0 Ω resistor. The voltage drop across the 2.0 Ω resistor is 5.0 V. What is its internal resistance?

a) 0.40 Ω
b) 1.7 Ω
c) 2.4 Ω
d) 2.5 Ω

VT=ε-Ir

## The Attempt at a Solution

I know that

ε=6.0 V
VT=5.0 V
and a resistor= 2.0 Ω

The resistor part is what I don't understand. If I'm looking for the internal resistance, I'm looking for the resistance of the resistor. So if they give me the resistance to be 2.0 Ω in the question, shouldn't the answer be 2.0?

The answer is a) 0.40 Ω.

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gneill
Mentor
1. A battery whose emf is 6.0 V is connected to a 2.0 Ω resistor. The voltage drop across the 2.0 Ω resistor is 5.0 V. What is its internal resistance?

a) 0.40 Ω
b) 1.7 Ω
c) 2.4 Ω
d) 2.5 Ω

VT=ε-Ir

## The Attempt at a Solution

I know that

ε=6.0 V
VT=5.0 V
and a resistor= 2.0 Ω

The resistor part is what I don't understand. If I'm looking for the internal resistance, I'm looking for the resistance of the resistor. So if they give me the resistance to be 2.0 Ω in the question, shouldn't the answer be 2.0?

The answer is a) 0.40 Ω.
You're looking for the internal resistance of the battery.