
For a cell terminal potential difference is 2.2 volt when circuit is open and reduces to 1.8 volt when cell is connected to an external resistance of 5 ohm. What is the internal resistance of the cell?
Answer
515.4k+ views
Hint: Draw the corresponding circuit diagram when the cell is connected across the resistance 0f 5 ohms. Shown the internal resistance r in series. It is given that the potential difference across 5 ohms is 1.8V. Hence, calculate the current using ohm’s law. Then by using ohm’s law calculate the internal resistance.
Formula used:
V=iR
Complete step by step answer:
Cell is a device that is used to create a potential difference in the circuit and thus there is flow of charges in the circuit. We define emf for a cell.
When the circuit is open and there is no current, the potential difference across the cell’s terminal is equal to emf E.
When the cell is connected across a resistance the cell creates a potential difference equal to E across the resistance (R) and due the potential difference, there is current in the circuit. The value of the current is .
However, every cell has a self resistance called internal resistance (r). Therefore, when a cell is connected across the resistance, the internal resistance contributes to the net resistance and thus the current in the circuit is less than then .
It is given that E=2.2V.
When the cell is connected across the resistance of 5 ohms, The potential difference across 5 ohms is 1.8V.
Let us make the diagram of the above circuit. The current in the circuit be i.
Let the potential difference across 5 ohms resistance be V. Then according to Ohm’s law, V=iR.
This implies,
.
Therefore current in the circuit is 0.36 A.
The potential difference that should have been created across the resistance of 5 ohms is 2.2V. However, due to the internal resistance, the potential difference across the resistance is 1.8V. That means the potential difference across r is 2.2-1.8=0.4V.
The current flowing through r is 0.36A.
Again use Ohm’s law.
Hence, we get
Therefore, the internal resistance of the cell is 1.11 ohms.
Note:
Note that internal resistance of a cell is inside the cell though in the diagram it is shown outside the cell. The internal resistance is the same as a normal resistance and takes up some potential difference. It is the same as connecting a resistance r in series to an ideal cell.
Formula used:
V=iR
Complete step by step answer:
Cell is a device that is used to create a potential difference in the circuit and thus there is flow of charges in the circuit. We define emf for a cell.
When the circuit is open and there is no current, the potential difference across the cell’s terminal is equal to emf E.
When the cell is connected across a resistance the cell creates a potential difference equal to E across the resistance (R) and due the potential difference, there is current in the circuit. The value of the current is
However, every cell has a self resistance called internal resistance (r). Therefore, when a cell is connected across the resistance, the internal resistance contributes to the net resistance and thus the current in the circuit is less than then
It is given that E=2.2V.
When the cell is connected across the resistance of 5 ohms, The potential difference across 5 ohms is 1.8V.
Let us make the diagram of the above circuit. The current in the circuit be i.

Let the potential difference across 5 ohms resistance be V. Then according to Ohm’s law, V=iR.
This implies,
Therefore current in the circuit is 0.36 A.
The potential difference that should have been created across the resistance of 5 ohms is 2.2V. However, due to the internal resistance, the potential difference across the resistance is 1.8V. That means the potential difference across r is 2.2-1.8=0.4V.
The current flowing through r is 0.36A.
Again use Ohm’s law.
Hence, we get
Therefore, the internal resistance of the cell is 1.11 ohms.
Note:
Note that internal resistance of a cell is inside the cell though in the diagram it is shown outside the cell. The internal resistance is the same as a normal resistance and takes up some potential difference. It is the same as connecting a resistance r in series to an ideal cell.
Recently Updated Pages
Master Class 12 Business Studies: Engaging Questions & Answers for Success

Master Class 12 English: Engaging Questions & Answers for Success

Master Class 12 Economics: Engaging Questions & Answers for Success

Master Class 12 Social Science: Engaging Questions & Answers for Success

Master Class 12 Maths: Engaging Questions & Answers for Success

Master Class 12 Chemistry: Engaging Questions & Answers for Success

Trending doubts
Why is insulin not administered orally to a diabetic class 12 biology CBSE

The total number of isomers considering both the structural class 12 chemistry CBSE

What is the Full Form of PVC, PET, HDPE, LDPE, PP and PS ?

How do you convert from joules to electron volts class 12 physics CBSE

Define Vant Hoff factor How is it related to the degree class 12 chemistry CBSE

The first microscope was invented by A Leeuwenhoek class 12 biology CBSE
