Change in voltage due to additional source

[Queequeg]

Homework Statement

A voltage source connected to a circuit produces a voltage V, current I and has internal resistance R. What is the new voltage if an identical voltage source is added to the original:

a) in parallel
b) in series

Homework Equations

V=IR[/B]

The Attempt at a Solution

a. For a voltage source in parallel, the equivalent resistance is R/2. Each source provides a current I so the total current is I+I=2I. Therefore the new voltage is V_n=(2I)(R/2)=IR=V unchanged

b. The equivalent resistance is 2R and the current is I because they are in series, so the new voltage is V_n=I(2R)=2V doubled.

 

[Bystander]

Did you have any further questions?

 

[gneill]

Homework Statement

A voltage source connected to a circuit produces a voltage V, current I and has internal resistance R. What is the new voltage if an identical voltage source is added to the original:

a) in parallel
b) in series

Homework Equations

V=IR[/B]

The Attempt at a Solution

a. For a voltage source in parallel, the equivalent resistance is R/2. Each source provides a current I so the total current is I+I=2I. Therefore the new voltage is V_n=(2I)(R/2)=IR=V unchanged

b. The equivalent resistance is 2R and the current is I because they are in series, so the new voltage is V_n=I(2R)=2V doubled.

What is the effect of the circuit to which the voltage supplies are connected? Presumably the voltage mentioned is meant to be the voltage across that load?

When you connect an identical source in parallel with the first, I agree that the effective internal resistance is halved while the effective cell voltage remains the same. But how will that effect the voltage V that is measured across the load resistance?

 

[CWatters]

The original question is badly worded. I suppose you had better assume the load is resistive.

 

[HalfLostAndSearching]

Your solution is correct. In both cases, the added voltage source does not change the total voltage in the circuit, but it does affect the current and the equivalent resistance. In parallel, the equivalent resistance decreases, resulting in a higher current and the same voltage. In series, the equivalent resistance increases, resulting in the same current and a higher voltage. This is an important concept to understand in circuit analysis and design.