Low resistances are provided with four terminalsa)To facilitate the c...
Low resistances are provided with four terminals in order that the resistance value becomes definite irrespective of nature of constants at the current terminals
Four terminal measurements are used for low resistance measurement to avoid contact resistances and the effect of measuring instrument on a measured value.
Two outermost terminals are used to inject current in the low-value resistance. Voltage is measured across two inner terminals. This ensures that any contact resistance drop at current terminals does not affect voltmeter reading.
The value of low resistance is measured between the potential terminal P and P’.
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Low resistances are provided with four terminalsa)To facilitate the c...
Explanation:
a) To facilitate the connection of current and potential circuits:
Four terminal resistors, also known as Kelvin resistors, have two separate pairs of terminals. This arrangement allows for the precise measurement of current and potential. The current terminals are used to pass the current through the resistor, while the potential terminals are used to measure the voltage drop across the resistor. By having separate terminals for current and potential, it becomes easier to connect the resistor to the current and potential circuits.
b) In order that the resistance value becomes definite irrespective of the nature of constants at the current terminals:
One of the main advantages of four terminal resistors is that they provide a definite resistance value, regardless of the nature of the constants at the current terminals. This means that the resistance value remains constant even if there are variations in the contact resistance or the resistance of the connecting leads. By having separate terminals for current and potential, the resistance value is measured directly at the potential terminals, eliminating any variations caused by the current terminals.
c) To eliminate the effect of thermo-electric emfs:
Thermo-electric emfs (electromotive forces) are voltages that are generated due to temperature differences at the junctions of different metals or conductors. These emfs can introduce errors in resistance measurements. However, by using four terminal resistors, the effect of thermo-electric emfs can be eliminated. This is because the potential terminals are connected directly to the resistor, bypassing any potential differences caused by the thermo-electric emfs.
d) To eliminate the effect leads:
In electrical circuits, the connecting leads between components can introduce resistance and affect the measurement accuracy. By using four terminal resistors, the effect of these connecting leads can be eliminated. This is because the current terminals are connected directly to the resistor, bypassing any resistance introduced by the leads.
Therefore, the correct answer is option 'B' - Four terminal resistors are provided to ensure that the resistance value becomes definite irrespective of the nature of constants at the current terminals.
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