Question

What is the meaning of calibration of voltmeter and ammeter? Explain the method of calibration of voltmeter with the help of potentiometer. Make the required circuit diagram and draw the calibration curve.

Answer 1

Hint: We define the calibration of voltmeter and ammeter and then their calibration with the use of potentiometer. The calibration is the process to check the correctness of the results by making their comparison with standard values.

Complete step by step solution:
Checking the accuracy of the instrument by measuring with standard results. It helps us to get the error occurred and get the ideal reading by making adjustments in voltage.
Calibration of voltmeter using potentiometer:-

The circuit has two rheostats, one for controlling voltage and other for making adjustment. Here the voltage box is to step down the voltage to a desired value so the accurate value of the voltmeter is determined by measuring the values of the voltage to the maximum possible range of the potentiometer.
The negative and the error occurred in voltmeter is the two voltages of potentiometer and voltmeter are not equal.
Calibration Curve: A graph is plotted between the readings of voltmeter and the corresponding errors. This graph is called the calibration curve of the voltmeter. The graph has no definite shape. The graph of calibration is shown in figure.
Calibration of ammeter using potentiometer:-
Standard resistor is connected in series with the ammeter which is to be calibrated. Potentiometer measures voltage across standard resistors. Current standard resistor is defined by:
\[
  I = \dfrac{{{V_s}}}{R} \\
  {V_s} = {\text{Voltage across standard resistor}} \\
  R = {\text{Resistance of standard resistor}} \\
 \]
This method of calibration is accurate hence, the resistance of standard resistor and potential across potentiometer is exactly known by instrument.
For different readings of ammeter to obtain corresponding real current by potentiometer then the corresponding error will be I – I’. Plotting the curve between I – I’ and I which is called the calibration curve of the ammeter. Zig-zag curve is obtained as shown in the figure . We can find real reading by calibrated curves.

Additional Information:
A voltmeter is an instrument used for measuring electric potential difference between two points in an electric circuit. It is connected in parallel. It usually has a high resistance so that it takes negligible current from the circuit.
An ammeter is a measuring instrument used to measure the current in a circuit. Electric currents are measured in amperes, hence the name. The ammeter is usually connected in series with the circuit in which the current is to be measured.
A potentiometer is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat.

Note:
The curve plotted using the voltmeter readings and the corresponding errors are called the calibration curve of the voltmeter. This curve does not have a particular shape. It can be of random shape. A voltmeter is used to measure the potential difference across two points.