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Measuring voltage and current in circuits

As we have seen in previous sections, an electric circuit is made up of a number of different components such as batteries, resistors andlight bulbs. There are devices to measure the properties of these components. These devices are called meters.

For example, one may be interested in measuring the amount of current flowing through a circuit using an ammeter or measuring the voltage provided by a battery using a voltmeter . In this section we will discuss the practical usage of voltmeters and ammeters.

Voltmeter

A voltmeter is an instrument for measuring the voltage between two points in an electric circuit. In analogy with a water circuit, avoltmeter is like a meter designed to measure pressure difference. Since one is interested in measuring the voltage between twopoints in a circuit, a voltmeter must be connected in parallel with the portion of the circuit on which the measurement is made.

A voltmeter should be connected in parallel in a circuit.

[link] shows a voltmeter connected in parallel with a battery. The positive lead of the voltmeter must be connected closest to the positive end of the battery and the negative lead closest to the negative end of the battery. The voltmeter may also be used to measure thevoltage across a resistor or any other component of a circuit that has a voltage drop or potential difference.

Ammeter

An ammeter is an instrument used to measure the flow of electric current in a circuit. Since one is interested in measuring thecurrent flowing through the circuit, the ammeter must be connected in series with the measured circuit component ( [link] ). The positive lead from the ammeter must be connected closest to the positive end of the battery and the negative lead must be connected closest to the negative end of the battery.

An ammeter should be connected in series in a circuit.

Impact of meters on circuits

A good quality meter used correctly will not significantly change the values it is used to measure. This means that an ammeter hasvery low resistance so as to not slow down the flow of charge. A voltmeter has a very high resistance so that it does not add another parallel pathway to the circuit for the charge to flow along.

Investigation : using meters

If possible, connect meters in circuits to get used to how to use meters tomeasure electrical quantities. If the meters have more than one scale, always connect to the largest scale first so that the meter will not be damaged by having to measure values that exceed itslimits.

The table below summarises the use of each measuring instrument that we discussed and the way it should be connected to a circuitcomponent.

Instrument Measured Quantity Proper Connection
Voltmeter Voltage In Parallel
Ammeter Current In Series

Resistance

The resistance of a circuit element can be thought of as how much it opposes the flow of electric current in the circuit.

Resistance

The resistance of a conductor is defined as the potential difference across it divided by the current flowing though it. We use the symbol R to show resistance and it is measured in units called Ohms with the symbol Ω .

1 Ohm = 1 Volt Ampere .

Questions & Answers

anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
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Damian Reply
absolutely yes
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Do somebody tell me a best nano engineering book for beginners?
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there is no specific books for beginners but there is book called principle of nanotechnology
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are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
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types of nano material
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I start with an easy one. carbon nanotubes woven into a long filament like a string
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Source:  OpenStax, Physics - grade 10 [caps 2011]. OpenStax CNX. Jun 14, 2011 Download for free at http://cnx.org/content/col11298/1.3
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