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  • A battery of emf 12V and internal resistance is connected to a <img alt="4\, \Omega" src="https://entrancecorner.codecogs.com/gif.latex?4%5C%2C%20%5COmega"

A battery of emf 12V and internal resistance 2\, \Omega is connected to a 4\, \Omega resistor as shown in the figure.
(a) Show that a voltmeter when placed across the cell and across the resistor in turn, gives the same reading,
(b) To record the voltage and the current in the circuit, why is voltmeter placed in parallel and ammeter in series in the circuit?

 

 

 

 
 
 
 
 

Answers (1)

a) The current through the circuit
I= \frac{12}{4+2}= 2A
Voltage across 4\, \Omega resistor
V_{4}= 4\times 2= 8V---(i)
here E= 12 \, V

The voltage across the cell
V= E-IR 
    = 12 -2\times 2
    =8\, V---(2)
From (1) & (2) it is clear that voltmeter, when placed across the resistor and across the cell, gives the same reading, that is 8\, V\cdot
b) If a voltmeter is connected in series due to high resistance of voltmeter it will draw a large amount of current and will not give the right voltage value across the circuit, so voltmeter is connected in parallel to the circuit whose voltage is to be measured.
Ammeter has very low internal resistance. if it is connected in parallel, the current flowing will not give a correct reading. So ammeter is always connected in series with the circuit.

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Safeer PP

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