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Question

A car battery has ___ resistance than a dry cell.


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Solution

The internal resistance of car battery and dry cell.

1. Inside the battery, current flows from the negative terminal to the positive terminal. So during this flow of current electrochemical factors (such as electrolyte conductivity, ion mobility, and electrode surface area) provide resistance to current.

2. This resistance knows as the internal resistance of the battery.

3. A normal dry cell is usually rated at 1.5v (terminal voltage =1.4V) and 100mA ) whereas a car battery is rated at 12V (terminal voltage =9V) and 200A.

4. Now using Ohm's law the internal resistance of the car's battery and dry cell can be calculated as r=E-Vi where E=emf of cell V=Terminal Voltage and i=Current in the circuit.

The internal resistance of the car's battery

r=12-9200

r=1.5×10-2Ω

Similarly for dry cell r=1.5-1.20.1

r=1Ω

Here we can see 1.5×10-2Ω << 1.0Ω . i.e. Internal resistance of the car's battery is much smaller than the resistance of the dry cell.

5. An enormous current of about 200A can only be generated when internal resistance is much lower.

6. A dry cell has an electrolyte in form of a paste that resists the flow of ions present.

7. The car battery generally consists of an electrolyte solution that is made up of 65%water and 35% sulphuric acid which makes ions flow easily leading to low resistance.

8. Internal resistance is a characteristic of the battery.

Hence, a car battery has much lower resistance than a dry cell.


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