As a result, it will not be possible to get perfect voltage across the load. In the end, the connection is made in parallel. Now, the voltage drop in parallel remains the same inspite of having resistors of different values. Save my name, email, and website in this browser for the next time I comment. Voltage Lab. Current flow through a galvanometer, I G , produces a proportional movement, or deflection, of the needle.
The two crucial characteristics of any galvanometer are its resistance and its current sensitivity. By connecting resistors to this galvanometer in different ways, you can use it as either a voltmeter or ammeter to measure a broad range of voltages or currents.
A galvanometer can function as a voltmeter when it is connected in series with a large resistance R. The value of R is determined by the maximum voltage that will be measured.
The total resistance must be:. R is so large that the galvanometer resistance, r, is nearly negligible. This voltmeter would not be useful for voltages less than about half a volt, because the meter deflection would be too small to read accurately.
For other voltage ranges, other resistances are placed in series with the galvanometer. Many meters allow a choice of scales, which involves switching an appropriate resistance into series with the galvanometer. The same galvanometer can also function as an ammeter when it is placed in parallel with a small resistance R , often called the shunt resistance. Since the shunt resistance is small, most of the current passes through it, allowing an ammeter to measure currents much greater than those that would produce a full-scale deflection of the galvanometer.
Suppose, for example, we need an ammeter that gives a full-scale deflection for 1. Since R and r are in parallel, the voltage across them is the same. Null measurements balance voltages so there is no current flowing through the measuring devices that would interfere with the measurement. Standard measurements of voltage and current alter circuits, introducing numerical uncertainties. Voltmeters draw some extra current, whereas ammeters reduce current flow. Null measurements balance voltages, so there is no current flowing through the measuring device and the circuit is unaltered.
Null measurements are generally more accurate but more complex than standard voltmeters and ammeters. Their precision is still limited. When measuring the EMF of a battery and connecting the battery directly to a standard voltmeter, as shown in, the actual quantity measured is the terminal voltage V. Voltmeter Connected to Battery : An analog voltmeter attached to a battery draws a small but nonzero current and measures a terminal voltage that differs from the EMF of the battery.
Note that the script capital E symbolizes electromotive force, or EMF. Since the internal resistance of the battery is not known precisely, it is not possible to calculate the EMF precisely. The EMF could be accurately calculated if r were known, which is rare. However, standard voltmeters need a current to operate. Class 10 Chapter 12 Class 10 - Electricity Term 2 Teachoo Questions Why is an ammeter connected in series and voltmeter connected in parallel?
Teachoo Questions What is the difference between resistance and resistivity? Why is an ammeter connected in series and voltmeter connected in parallel? You are here What is the difference between open and closed circuits?
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