# Internal Resistance problem when batteries are connected in opposition

• andipandi
In summary, the resultant emf in the given circuit with two batteries and a resistor connected in series is 18V. The rule behind this is that the emf in a circuit is the sum of the individual emfs, and in this case, one of the batteries is facing the opposite way, resulting in the emf of one battery being subtracted from the other. The resistances in the circuit do not affect the calculation of the resultant emf.
andipandi
A simple circuit with 2 batteries and a resistor connected in series. The positive terminals are connected to each other via a 4.5 resistor. Their emfs and internal resistances are below. What is the resultant emf?
battery 1: ε=6V r=1Ω
battery 2: ε=24V r=0.5Ω
resistor connecting the two batteries is 4.5Ω

(I've attached a picture of the circuit diagram)

The answer is 18V. I know that resultant emf =ε - Ir. But I have no idea how to achieve an answer when their are two batteries present, let alone connected in opposition. I've spent the past two hours research books and the internet with nothing to show of it. The only way I can see to get 18V would be to simply minus emf of battery 1 from battery2, if this is correct rather than a coincidence, what is the rule behind it?

#### Attachments

• q10.png
6.7 KB · Views: 1,025
Last edited:
welcome to pf!

hi andipandi! welcome to pf!
andipandi said:
The only way I can see to get 18V would be to simply minus emf of battery 1 from battery2, if this is correct rather than a coincidence, what is the rule behind it?

i've no idea why they tell you all about the resistances

the emf in a circuit (a loop) is simply the sum of the individual emfs

(and you can see from the long and short lines that the batteries are "facing" opposite ways, so one of them will be minus the other)

## What is internal resistance in batteries?

Internal resistance is the resistance that a battery's internal components have to the flow of electric current. It is caused by the resistance of the battery's electrodes, electrolyte, and other internal materials.

## Why does internal resistance cause a problem when batteries are connected in opposition?

When batteries are connected in opposition, their internal resistances are also connected in series. This means that the total internal resistance of the circuit increases, resulting in a decrease in the overall voltage and current output of the batteries.

## What are the effects of internal resistance on battery performance?

Internal resistance can cause a decrease in the voltage and current output of batteries, leading to a shorter lifespan and reduced overall performance. It can also cause the batteries to heat up, which can further decrease their efficiency and potentially damage the batteries.

## How can internal resistance be reduced?

Internal resistance can be reduced by using batteries with lower internal resistance, or by connecting multiple batteries in parallel instead of in opposition. Additionally, keeping the batteries at a moderate temperature can also help reduce internal resistance.

## Are there any other factors that can affect internal resistance in batteries?

Yes, there are several other factors that can affect internal resistance in batteries, such as the type and quality of the materials used in the battery, the age and condition of the battery, and the temperature. High temperatures can increase internal resistance, while low temperatures can decrease it.

Replies
10
Views
477
Replies
3
Views
661
Replies
4
Views
827
Replies
24
Views
4K
Replies
8
Views
2K
Replies
8
Views
12K
Replies
2
Views
2K
Replies
4
Views
2K
Replies
10
Views
3K
Replies
11
Views
5K