Question

which of the following measured by the Kelvin's is double bridge method
a) Low R
b) High R
c) Low L
d) none​

Answer 1

Answer:

A Kelvin bridge, also called a Kelvin double bridge and in some countries a Thomson bridge, is a measuring instrument used to measure unknown electrical resistors below 1 ohm. It is specifically designed to measure resistors that are constructed as four terminal resistors.

Option D)

Answer 2

$\huge\fbox\pink{Hi mate}$

Which of the following measured by the Kelvin's is double bridge method

a) Low R

b) High R

c) Low L

d) none

Answer

Option d) None is your answer

$\Large\fbox\blue{Reason}$

To understand the need of Kelvin bridge let us categorize the electrical resistances on the basis of view point of measurement: Electrical resistances are classified as follows:

$\Large\underline\red{High Resistance :}$

Under this category resistance is greater than 0.1 Mega-ohm.

$\Large\underline\red{Medium Resistance :}$

Under this category resistance is ranging from 1 ohm to 0.1 Mega-ohm.

$\Large\underline\red{Low Resistance}$

Under this category resistance value is lower than 1 ohm.

Now the logic of doing this classification is that if we want to measure electrical resistance, we have to use different devices for different categories. It means if the device is used in measuring the high Resistance gives high accuracy, it may or may not give such high accuracy in measuring the low value of resistance.

So, we have to apply our brain to judge what device must be used to measure a particular value of electrical resistance. However there are other kind of methods also like ammeter-voltmeter method, substitution method etc but they give large error as compared to bridge method and are avoided in most of the industries.

Now let us again recall our classification done above, as we move from top to bottom the value of resistance decreases hence, we require more accurate and precise device to measure the low value of resistance.

One of the major drawback of the Wheatstone bridge is that, it can measure the resistance from few ohm to several mega ohm but to measure low resistance it gives significant error.

So, we need some modification in Wheatstone bridge itself, and the modified bridge so obtained is Kelvin bridge, which is not only suitable for measuring low value of resistance but has wide range of applications in the industrial world.

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