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Why does an ammeter have a low resistance while a voltmeter has high resistance?
Wiki User
∙ 11y ago
I am going to assume that you mean low "resistance" in an open circuit test and are performing this with a multimeter. An ammeter works by place a very small amount of resistance in series with a circuit and then measuring the Voltage drop across the resistance. The Voltage is directly proportional to the current as given in ohms law: E = I x R If you are measuring the resistance through the ammeter it will have a very low resistance and impedance.
Wiki User
∙ 14y ago
Wiki User
∙ 11y agoSo they do not load the circuit / insert an unwanted voltage drop in the circuit. Since the voltage across the ammeter is equivalent to the resistance of the ammeter times the current through the meter, it is necessary to minimize the ammeter's resistance.
Ammeters, which are connected in series in a circuit when used, work by using a very small amount of resistance with a knownvalue, and then measuring the voltage drop across that to determine current flow. In order for an ammeter to be used without significantly affecting circuit operation, it must present as little resistance as possible to the circuit in which it is being used.
Ammeters are connected in series with the circuit where they are being used in the measurement of current. Thus, ideally there should be zero voltage drop across ammeter. The only way this is possible is if they have a zero internal resistance. They can't have an internal resistance of zero, but we need to keep it as low as possible.
We know that voltage drop across a given resistance is directly proportional to its resistance. By measuring the voltage drop across a known resistance, we can find current flow, and this is what an ammeter does. To minimise the voltage drop across an ammeter when it is connected in series with a circuit, it is designed with a very low internal resistance.
Wiki User
∙ 11y agoAnswer
So that their inclusion in the circuit doesn't interfere with the operation of the circuit.
Answer
Ammeter always connect in series for the measurement of current,so it should be very low resistance.if it has large resistance there no current flow in the ckt.and no measurement
A voltmeter always connect in parallel to measure the voltage,if voltmeter has very small resistance there is short ckt. and no current flow through the load and no measurement,so a voltmeter is always connect in parallel and should have very large resistance
Answer
First you should understand that both ammeter and voltmeter are basically the same consisting of coil which is attached to a needle which determines the magnitude of the input.
For voltmeter, high resistance is required to limit the current in the coil so it won't exceed its rated current value.
For ammeter, ammeters don't actually measure current instead they measure the voltage across the shunt resistance of known value, then by ohm's law:
I=V/R
it shows its output and shunt is always connected in parallel of the meter because the coil cannot handle large currents.
Wiki User
∙ 12y agoLike Voltmeter,Ammeter is also a kind of Electrical Measuring Instrument that measures magnitude of Electric current through the branch.Ammeter is always connected in series in a circuit.
In case,the resistance of ammeter is kept high,the ammeter will make a large proportion of the series resistance of the circuit and consequently will reduce current value supplied by the source.
The reduced current value will highlight in the form of error in the actual current value required by the load.The ammeter reading hence will be disturbed and get erroneous.
To avoid such erroneous result,resistance of ammeter is kept very low.
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What would happen if a voltmeter were substituted for an ammeter?
Smoke. Since a voltmeter is in parallel with the load it is right across the source voltage. Putting the amp meter across the line with its low resistance it will act like a fuse, hence the smoke. Newer solid state testers are usually smarter that the operators. They have built in circuitry which sense the wrong settings you are using and shut the tester off with a "beep" to let you know that you are doing something wrong.
What is the difference between ammeters and amp meters?
An Ammeter connects a low impedance on the test points, so the equivalent of that is a "short circuit" between the test points. This is done to avoid a drop of current on the tested circuit. A Voltmeter connects a high impedance on the test points, so the equivalent of that is a "open circuit" between the test points. This is done to avoid a drop of voltage on the tested circuit. --------- In terms of external connections Ammeter (used to measure current) is connected in series of the circuit (through which the current flow need to be measured) and voltmeter (used to measure voltage) is connected in parallel to points in circuit (across which voltage needs to be measured).
What is the use of universal high resistance voltmeter?
A voltmeter must have a very high resistance to measure voltage. A voltmeter is placed in parallel with the element that you are measuring. If the voltmeter has a low internal resistance, then all of the current will flow through the voltmeter instead of the element. You want all of the current to flow through the element, to get an accurate reading of the voltage. Conversely, an ampmeter must have zero resistance, because it is placed in series with the element.
What would be the resistance of an ideal voltmeter?
The theoretical resistance (idea resistance) of an ammeter is zero. With a voltmeter, it's infinitely high. In some analog meters the full scale deflection is produced by only about 50 microamps. Actually that does not change from ammeter to voltmeter, just the configuration of the meter's external "connection circuit"changes. Simple ammeters are 'connected in series' devices. The resistance of such an ammeter must be kept very low because, if it were a high resistance, that would seriously limit the current allowed into the circuit and would impair the circuit's function. Voltmeters are 'connected in parallel' devices. The theoretical resistance of a volt meter is very high, the higher the better. It is checking the potential between two points, so, to have the least effect on the circuit it is measuring, it must draw as little current as possible.
What will happen if a voltmeter has a low shunt resistance instead of having high shunt resistance?
The purpose of a voltmeter is to indicate the potential difference between two points in a circuit.When a voltmeter is connected across a circuit, it shunts the circuit. If the voltmeter has a low resistance,it will draw a substantial amount of current. This action lowers the effective resistance of the circuit andchanges the voltage reading.
High resistance in parallel connected with galvanometer to form voltmeter?
That won't work. To convert an ammeter (a galvanometer is a very sensitive type of ammeter) you connect a high value resistor in series with it.
Which will normally have the larger resistance a voltmeter or an ammeter?
A voltmeter has the large resistance.The voltage across any component can be measured if & only if the terminals of that component will be open and this will we can acheiv if we connect the high resistance voltmeter across the open terminals of that component to measure the voltage.
What would happen if a voltmeter were substituted for an ammeter?
Smoke. Since a voltmeter is in parallel with the load it is right across the source voltage. Putting the amp meter across the line with its low resistance it will act like a fuse, hence the smoke. Newer solid state testers are usually smarter that the operators. They have built in circuitry which sense the wrong settings you are using and shut the tester off with a "beep" to let you know that you are doing something wrong.
How is an ammeter converted to a voltmeter?
The ammeter is used in series, because you want to measure the current through a circuit. The voltmeter is used in parallel, because you want to measure the voltage across a circuit. If you were to place the voltmeter in series, no current would flow because of the relatively high impedance of the voltmeter. If you were to place the ammeter in parallel, you would create a short-circuit, due to the relatively low impedance of the ammeter.
What is the calibration of ammeter?
An ammeter should not be used as a voltmeter. An ammeter is a low impedance device that measures the current going through a circuit, often by measuring the small voltage across a known resistance. A voltmeter is a high impedance device that measures the voltage across a circuit. If you were to connect an ammeter as if it were a voltmeter, you would effectively short out the circuit, drastically affecting its operation, and potentially damaging both the circuit and the ammeter.
Battery connected to high Resistance voltmeter the reading is 1.5V when it is shorted on a low resistance ammeter the current is 2.5A what is the emf and the internal resistance of the battery?
The Thevenin equivalent circuit of this battery is 1.5V and 0.6 ohms in series. A more exact answer cannot be given without knowing the actual resistance of the 2 meters (I assumed infinite for the voltmeter and zero for the ammeter, as would be for ideal meters).However I would NEVER attempt this test as you describe it, many types of batteries will explode like bombs when shorted (as they would be when an ammeter was placed across them)! The correct way to do this test safely is with just a voltmeter and an adjustable high wattage resistor.
What is the difference between ammeters and amp meters?
An Ammeter connects a low impedance on the test points, so the equivalent of that is a "short circuit" between the test points. This is done to avoid a drop of current on the tested circuit. A Voltmeter connects a high impedance on the test points, so the equivalent of that is a "open circuit" between the test points. This is done to avoid a drop of voltage on the tested circuit. --------- In terms of external connections Ammeter (used to measure current) is connected in series of the circuit (through which the current flow need to be measured) and voltmeter (used to measure voltage) is connected in parallel to points in circuit (across which voltage needs to be measured).
Why does voltmeter have high internal resistance?
No, ammeters have a low internal resistance. This is so that when they are put in series with a circuit, they change the circuit's operating characteristics as little as possible.Contrast this with voltmeters, which do have a high internal resistance, and which are intended to be placed in parallel with the circuit they are measuring.Use the link below to the related question on why ammeters have a low internal resistance and read through that information to see why things are the way they are.
How does the loading effect of an ammeter in a low resistance circuit compare to the loading effect in a high resistance circuit?
The voltmeter has an internal resistance, which should be as high as possible. As this resistance draws current from the circuit under test, it will affect circuit operation. This is more pronounced in a high impedance circuit because the current drawn flows through higher resistances.
What happens when an ammeter is connected in parallel?
It would be equivalent to adding a high value resistor (>10M ohms) in series in the circuit. Voltmeters typically present a high internal impedance so as to not change the current flow in the circuit you are tying to measure. the circuit wont work the voltmeter only takes a voltage reading power does not actually pass through the meter sometimes it can be used to measure very low leakage current using the hi impedance of the meter. EXAMPLE leakage offset from an amplifier. it could be into the nanoamps.
Ideal universal high resistance voltmeter?
The ideal, or theoretical, voltmeter has infinite resistance, which means that, at any measured voltage, there is no current through the voltmeter. In the practical world, this is impossible, but there are high resistance voltmeters that minimize the error introduced by drawing a current from a circuit. A typical digital voltmeter has 10 to 20 megohms of resistance, and there are high performance versions that can have thousands of megohms of resistance, or more.
What instrument is used when performing a high-rate discharge test on a storage battery?
A voltmeter and an ammeter
