In an experiment of calibartion of voltmeter, a standard cell of emf `1.1 V` is balanced against `440 cm` of potentiometer wire. The potentilal difference across the ends of a resistance is found to balance against `220 cm` of the wire. The corresponding reading of voltmeter is 0.5 volt. Find the error in the reading of voltmeter.

Options

A. `-0.15" volts"`
B. `"0.15 volts"`
C. `"0.5 volts"`
D. `-0.05" volts"`

Answer

D

Explanation

In a voltmeter
`V prop l" "V =kl`
Now, it is given `E=1.1` volt for `l_(1)=440 cm`
and `V=0.5 " volt for "l_(2)=220 cm`
Let the error in reading of voltmeter be `DeltaV` then,
`1.1=400 K and (0.5-DeltaV)=220K`.
`rArr" "(1.1)/(440)=(0.5-DeltaV)/(220)" "therefore" "DeltaV=-0.05" volt"`