 QUESTION

# A voltmeter has a least count of 0.05 volt, while doing Ohm's law experiment a student observed that the pointer of the voltmeter coincides with the 15th division. The observed reading isA. 0.75 VB. 0.075 VC. 7.5 VD. 75 V

Hint: Let us use the result which states that least count is equal to the minimum reading that instrument can take.

As we know that least count is the value of one smallest one division present in any measuring instrument.

So, it is obvious that if the least count of any instrument is x. And the pointer is at ${n^{th}}$ division. Then the value of ${n^{th}}$ division will be equal to n*(least count). Because the least count is the value of one division.

So, here we are given that the least count of the voltmeter is 0.05 volts.

And the pointer of the voltmeter coincides with the 15th division. So, n = 15.
So, the observed reading will be the reading of 15th division and that will be equal to (least count)*n = 0.05*15 = 0.75 volts.

So, the observed reading of the voltmeter will be 0.75 volts.

Hence, the correct option will be A.

Note: Whenever we come up with a type of problem then we should remember that the least count of any measuring instrument is the value of smallest division in that instrument. So, observed value at ${n^{th}}$ division will be equal to n*(least count).