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 15th division. The observed reading is:
(a). 0.75V
(b). 0.075V
(c). 7.5V
(d). 75V

Answer 1

- Hint: A voltmeter is an instrument used for measuring voltage or potential variation amid two points in a circuit.

Complete step-by-step solution -

In physics, when we deal with measurements, there are various instruments available. To measure current, we use ammeter, to measure voltage, we use voltmeter. There is even a multimixer available that allows the measurement of current, voltage, capacitance and resistance. These instruments are available in Analog and in Digital type.
Analog voltmeter has a pointer across the scale which is in proportion to the voltage of the circuit. Digital voltmeter gives a number display of voltage by using an ADC converter (Analog to Digital converter)
Every voltmeter will have an impedance which is its internal resistance. The impedance of an Analog voltmeter is expressed in ohms per volt. Digital voltmeters have a fixed usually 10M ohms or more resistance. Hence, we can say that digital voltmeters have high resistance which does not change from scale to scale as in analogy voltmeter which makes it more accurate than the conventional analogy voltmeters.
To measure voltage, we can use ohm’s law which states that the current flowing through a conductor between two points is directly proportional to the voltage across the two points.
\[\text{V=IR}\],
Where V is voltage in volts(V), I is current in amperes(A) and R is a constant resistance in ohms(Ω).
The formula to calculate the voltage given its least count is given by,
\[\text{Voltage=least count x no of divisions}\],
\[\text{Voltage=0}\text{.05V x 15= 0}\text{.75V}\],
Substituting least count as 0.05V and the no of division as 15, we get the voltage of 0.75V.
Hence, the observed reading in the voltmeter is 0.75V.

Note: Digital Voltmeters will be more precise values than Analog Voltmeters as they have fixed resistance in them. Analog Voltmeters always change their values according to their scale.