Why ammeter is used in series

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Enter your name or username to comment. Voltmeters and ammeters measure the voltage and current, respectively, of a circuit. Some meters in automobile dashboards, digital cameras, cell phones, and tuner-amplifiers are voltmeters or ammeters. Voltmeters and Ammeters : A brief introduction to voltmeters and ammeters for introductory physics students. A voltmeter is an instrument that measures the difference in electrical potential between two points in an electric circuit.

Any measurement that can be converted to voltage can be displayed on a meter that is properly calibrated; such measurements include pressure, temperature, and flow.

This is necessary because objects in parallel experience the same potential difference. Voltmeter in Parallel : a To measure the potential difference in this series circuit, the voltmeter V is placed in parallel with the voltage source or either of the resistors.

Note that terminal voltage is measured between points a and b. It is not possible to connect the voltmeter directly across the EMF without including its internal resistance, r. An ammeter measures the electric current in a circuit. The name is derived from the name for the SI unit for electric current, amperes A. This is necessary because objects in series experience the same current.

They must not be connected to a voltage source — ammeters are designed to work under a minimal burden, which refers to the voltage drop across the ammeter, typically a small fraction of a volt. Ammeter in Series : An ammeter A is placed in series to measure current.

All of the current in this circuit flows through the meter. The ammeter would have the same reading if located between points d and e or between points f and a, as it does in the position shown.

Note that the script capital E stands for EMF, and r stands for the internal resistance of the source of potential difference. Analog meters have needles that swivel to point at numbers on a scale, as opposed to digital meters, which have numerical readouts.

The heart of most analog meters is a device called a galvanometer, denoted by G. 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.