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Why does the voltmeter input have a much higher resistance than the current input?
Wiki User
∙ 12y ago
Anything that a voltmeter is measuring has some internal output impedance. If the voltmeter had a low input impedance, these two impedances would form a voltage divider and reduce the voltage measured.
The voltmeter has a high input impedance so that it does not affect ("load down") the thing it is measuring.
Wiki User
∙ 15y ago
Wiki User
∙ 12y agoVoltage is a measure of the voltage drop across two terminals. Voltage is measured with a parallel circuit, and you don't need much current through the drop resistor to get the E = IR calculation. Current is measured with a series circuit. To measure micro-amps or milli-amps, you need a small resistance to allow enough current to drop across the sensing resistor to measure the I = V/R calculation. However, multimeters have a range switch for higher or lower currents, as well as higher or lower voltages. If you use the low range for high current or voltage you could damage the meter.
Wiki User
∙ 12y agoIn a circuit, voltmeters are connected in parallel across the element which it is measuring the potential difference. Since you don't want the current diverted through the voltmeter, the voltmeter has a high internal resistance so that the circuit maintains the same current as if the voltmeter was not present.
Similarly, ammeters are connected in series and have very low internal resistance.
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Is a resistor an input?
A Resistor does exactly what the name suggests, it creates resistance. More precisely, it creates resistance for the flow of electrons, effectively limiting the amount of current flowing through it(and via ohms law, limits voltage). To answer the question, A resistor isn't an input or output device, it behaves the same way no matter how you turn it and it can be placed on the input of a component(or circuit) aswell as the output.
Ratio or amplifier output signal to its input?
It never referred as ratio but Rather a gain A in the form of output divided by the input and implies voltage A=gain. basically is input resistance divided by the feedback resistance
Why is output dc higher than input ac?
Output power can never be more than input power. With a transformer, it is possible to increase the output current (while decreasing the output voltage), or to decrease the output current (while increasing the output voltage).
Does voltage regulator increase or decrease the current input?
A DC voltage regulator gives a constant output voltage provided the input voltage is at least 1.5 v higher, up to a given limit. The input current is slightly more than the load current, because a small amoutn of current is needed for the voltage regulator circuit. Check the datasheet of the component which you are using to find the limits. 7805 IC can give upto 1A of current if there is adequete heatsinking.
What kind of device is a resistor?
A Resistor does exactly what the name suggests, it creates resistance. More precisely, it creates resistance for the flow of electrons, effectively limiting the amount of current flowing through it(and via ohms law, limits voltage). To answer the question, A resistor isn't an input or output device, it behaves the same way no matter how you turn it and it can be placed on the input of a component(or circuit) aswell as the output.
What does 10 megohm input impedance mean?
10 megohms is the resistance through which 10 volts would push 10 microamps of current. Input impedance is the resistance seen by a signal source when connected to the input Often, this means there is a 10 megohm resistor in series with the input going to a virtual ground on an opamp circuit. 10 megohms is a common input impedance for a digital voltmeter.
In modern electronic multimeter a fet or mosfet is preferred over bjt because?
Because of its much higher input impedance. When measuring voltage, that makes the voltmeter appear to the circuit as if it's not there, so the presence of the voltmeter doesn't change the operation of the circuit.
How can you measure high resistance?
using a high resistance-ometer ANSWER: Some commercial voltmeter have an input impedance of 11 mega ohms So instead of measuring across the resistance you may put the meter in series that will give you a voltage drop due to current that can be calculated to find the other resistance
How do design a high voltage voltmeter?
Use a voltage divider and an standard high input impedance voltmeter connected to the low voltage output tap of the divider. Just check that: a) the voltage divider has enough resistance to minimize loading of the voltage source (The voltage divider resistance should be as high as possible). b) the voltmeter's input impedance is at least 10-20 times larger than the output resistance (impedance) of the divider. If necessary add a high-input impedance amplifier or a transducer between the divider output and the voltmeter. What is high voltage for you?
What is voltmeter sensitivity?
Voltmeters are connected in parallel with the components whose voltage or voltage drop you want to measure. That means that the internal voltmeter's resistance will create a new branch in parallel with the component, thus increasing the current in the circuit. If there are other components in series with the component to which the voltmeter is connected, this increment of current will increase the voltage drop across them, reducing the voltage drop across the component whose voltage is being measured. This is obviously an induced error in the measurement, which adds up to other errors built into the voltmeter (accuracy, resolution, linearity, parallax, etc.) When measuring the output voltage of low resistance (high current) power supplies, the input impedance is usually not an issue. However, when measuring a low current power supply, the input resistance of the voltmeter will have to be at least 10 times the internal resistance of the power supply. Otherwise, the error will be too noticeable. Therefore, the ideal voltmeter should have an infinite internal resistance. Since this is not the case, it should at least have several megohms. Analog voltmeters usually have s sensitivity of 20 to 30 kilohm per volt (kΩ/V), which varies withe the voltmeter range setting. Digital voltmeters, instead, have constant high (>20 megohms) input impedance, which is a combination of pure resistance and reactance, usually capacitive, regardless of the voltage range. That is why the specs of a digital voltmeter always indicate the input capacitance.
Does a Digital Voltmeter have a high or low input impedance?
Digital voltmeter has high input impedence.
How does the loading effect of a voltmeter in a high-rsistance circuit compare to the loading effect in a low-resistance circult?
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.
How a transistor transfers resistance?
The input current of transistor is approximately equal to output current .Suppose in common base configuration the emmiter current is approximately equal to collector current if neglect the very small value of bae current.Even though the input resistance is not equal to output resistance,the currents are same ,so we can reliase that the transistor transfers resistance to get same currents at both ends.
Why input is voltage and output is current in fet?
The input is a Gate that is essentially infinite impedance, so no current. The output is essentially the resistance between Source and Drain, which controls the current flowing through it.
How a transistor work as an amplifier and as a switch?
"Transistor" name itself revels it transfers resistance from its input to its output (Transfer of resistance). Input resistance varies when input voltage varies, similarly output resistance varies and this leads to voltage variation at the output. Thus input to output voltage variation is called amplification. this is how transistor can be used as an amplifier. If input voltage is minimum output voltage becomes maximum i.e. its output resistance becomes maximum in common emitter configuration. Thus if no voltage is applied at the input its collector resistance becomes infinite or as if open circuit. Similarly if input current is increased output current increases and out put can behave as short circuit. This is how output current can be switched off or on using no input current or with minute input current. Unlike a digital device, the transistor is an analogue device which can be switch on/off to maximum or any gradient in between. Providing a small AC voltage to the base creates an amplified analogue of this signal across the emitter and collector.
What is the input resistance of an ideal current-measuring DMM?
First of all, DMM stands for Digital Multimeter. The -multi implies the meter measures several different parameters, usually voltage, current, resistance, and sometimes other things such as frequency. The input characteristics of a DMM will be very different depending on the parameter selected. For current, the ideal meter would have zero input resistance. Since the ammeter is inserted in series with the circuit under test, any resistance will alter the measured current, introducing error in the measurement.
Why the resistance of a capacitor is infinite when measures with an ohmmeter?
The typical ohmmeter measures DC resistance by providing DC current and measuring the voltage drop accross the resistor. By definition, the 'ideal' capacitor is an open circuit to DC current and voltage. By definition, an open circuit has infinite resistance. Of course, real-world capacitors are not ideal. They have a very high parallel leakage resistance and a very small series resistance. And, different meters can measure different ranges of resistance. So, you may not get an infinite/overload measurement on some capacitors with some meters. You may get a very high resistance instead. If so, you are not really measuring the resistance of the 'capacitor', but rather that of the imperfections in the component manufactured to be a capacitor. ANSWER: The ohmmeter battery will charge the capacitor in 5 time RC after that it quirts there is no more current flow. Any body that claim to be able to check resistance of a capacitor i just a wannabe
