shunt resistance

(noun)

a small resistance R placed in parallel with a galvanometer G to produce an ammeter; the larger the current to be measured, the smaller R must be; most of the current flowing through the meter is shunted through R to protect the galvanometer

Related Terms

  • galvanometer

Examples of shunt resistance in the following topics:

  • Voltmeters and Ammeters

    • The two crucial characteristics of any galvanometer are its resistance and its current sensitivity.
    • The total resistance must be:
    • For other voltage ranges, other resistances are placed in 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.
  • Resistance and Resistivity

    • Resistance and resistivity describe the extent to which an object or material impedes the flow of electric current.
    • Conductance and resistance are reciprocals .
    • What determines resistivity?
    • Its resistance to the flow of current is similar to the resistance posed by a pipe to fluid flow.
    • Identify properties of the material that are described by the resistance and resistivity
  • Dependence of Resistance on Temperature

    • Resistivity and resistance depend on temperature with the dependence being linear for small temperature changes and nonlinear for large.
    • The resistivity of all materials depends on temperature.
    • where ρ0 is the original resistivity and α is the temperature coefficient of resistivity.
    • is the temperature dependence of the resistance of an object, where R0 is the original resistance and R is the resistance after a temperature change T.
    • Compare temperature dependence of resistivity and resistance for large and small temperature changes
  • Resisitors in Series

    • The total resistance in the circuit with resistors connected in series is equal to the sum of the individual resistances.
    • A measure of this limit on charge flow is called resistance.
    • The total resistance in the circuit is equal to the sum of the individual resistances, since the current has to pass through each resistor in sequence through the circuit.
    • This implies that the total resistance in a series is equal to the sum of the individual resistances.
    • Since all of the current must pass through each resistor, it experiences the resistance of each, and resistances in series simply add up.
  • Combination Circuits

    • This is commonly encountered, especially when wire resistances is considered.
    • In that case, wire resistance is in series with other resistances that are in parallel.
    • Essentially, wire resistance is a series with the resistor.
    • It thus increases the total resistance and decreases the current.
    • Each is identified and reduced to an equivalent resistance, and these are further reduced until a single equivalent resistance is reached.
  • Current and Voltage Measurements in Circuits

    • The electrical current is directly proportional to the voltage applied and inversely related to the resistance in a circuit.
    • The electric property that impedes current (crudely similar to friction and air resistance) is called resistance R.
    • Resistance is inversely proportional to current.
    • Using this equation, we can calculate the current, voltage, or resistance in a given circuit.
    • Describe the relationship between the electrical current, voltage, and resistance in a circuit
  • Resistors in Parallel

    • The total resistance in a parallel circuit is equal to the sum of the inverse of each individual resistances.
    • This implies that the total resistance in a parallel circuit is equal to the sum of the inverse of each individual resistances.
    • This relationship results in a total resistance that is less than the smallest of the individual resistances.
    • Three resistors connected in parallel to a battery and the equivalent single or parallel resistance.
    • Calculate the total resistance in the circuit with resistors connected in parallel
  • Charging a Battery: EMFs in Series and Parallel

    • When voltage sources are connected in series, their emfs and internal resistances are additive; in parallel, they stay the same.
    • The disadvantage of series connections of cells in this manner, though, is that their internal resistances add.
    • But the total internal resistance is reduced, since the internal resistances are in parallel.
    • Current flows in the direction of the greater emf and is limited by the sum of the internal resistances.
    • This schematic represents a flashlight with two cells (voltage sources) and a single bulb (load resistance) in series.
  • Ohm's Law

    • Example: Calculating Resistance: An Automobile Headlight What is the resistance of an automobile headlight through which 2.50 A flows when 12.0 V is applied to it?
    • Discussion: This is a relatively small resistance, but it is larger than the cold resistance of the headlight.
    • As we shall see in Resistance and Resistivity, resistance usually increases with temperature, and so the bulb has a lower resistance when it is first switched on and will draw considerably more current during its brief warm-up period.
    • The unit for resistance is the ohm where 1Ω = 1 V/A.
    • An object that has simple resistance is called a resistor, even if its resistance is small .
  • Null Measurements

    • Many so-called ohmmeters measure resistance.
    • Most common ohmmeters apply a voltage to a resistance, measure the current, and calculate the resistance using Ohm's law.
    • Their readout is this calculated resistance.
    • The Wheatstone bridge is used to calculate unknown resistances.
    • The unknown EMF is thus proportional to the resistance of the wire segment.
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