The Kelvin double bridge is used to measure valued resistances and has resistors in its construction.

Question

Suresh said, "I did it yesterday."
Which one of the following options is the correct form of this sentence in indirect speech?

Answer 1

The Kelvin double bridge is a specialised measurement circuit, and this question checks whether the resistance range and the resistor construction it is built around are both remembered correctly. Look at each option pair in turn.

low ; three-terminal: Gets the resistance range right, since the Kelvin bridge is built for low resistances, but three-terminal resistors do not provide the separate current and potential connections the bridge design depends on, so this option is wrong.
low ; four-terminal: A plain Wheatstone bridge loses accuracy below roughly $1\ \Omega$ because lead and contact resistance become significant compared with the resistance being measured. The Kelvin double bridge fixes this by using four-terminal resistors, with separate current terminals and potential terminals, plus a second pair of ratio arms, so that the resistance of the link joining the two low resistors cancels out of the result. Both parts of this statement match the actual design, so it is correct.
high ; three-terminal: Wrong on both counts. High resistances are not the target application, and three-terminal construction cannot separate current flow from voltage sensing.
high ; four-terminal: The resistor description is right, but the resistance range is wrong. High-valued resistances are usually measured with a Wheatstone bridge or the loss-of-charge method, where lead resistance is small enough to ignore, so a Kelvin bridge is not needed there.

The correct statement is that the Kelvin double bridge measures low valued resistances using four-terminal resistors, matching option (B).

Let's summarize:

The Kelvin double bridge exists to remove lead and contact resistance error in low-resistance measurement.
Four-terminal resistors, with separate current and potential terminals, are what makes that error cancellation possible.
High resistances are measured by other methods where lead resistance is not a significant source of error.

So the blanks are filled as "low" and "four-terminal", option (B).

Answer 2

The Kelvin double bridge is a specialised measurement circuit, and this question checks whether the resistance range and the resistor construction it is built around are both remembered correctly. Look at each option pair in turn.

low ; three-terminal: Gets the resistance range right, since the Kelvin bridge is built for low resistances, but three-terminal resistors do not provide the separate current and potential connections the bridge design depends on, so this option is wrong.
low ; four-terminal: A plain Wheatstone bridge loses accuracy below roughly $1\ \Omega$ because lead and contact resistance become significant compared with the resistance being measured. The Kelvin double bridge fixes this by using four-terminal resistors, with separate current terminals and potential terminals, plus a second pair of ratio arms, so that the resistance of the link joining the two low resistors cancels out of the result. Both parts of this statement match the actual design, so it is correct.
high ; three-terminal: Wrong on both counts. High resistances are not the target application, and three-terminal construction cannot separate current flow from voltage sensing.
high ; four-terminal: The resistor description is right, but the resistance range is wrong. High-valued resistances are usually measured with a Wheatstone bridge or the loss-of-charge method, where lead resistance is small enough to ignore, so a Kelvin bridge is not needed there.

The correct statement is that the Kelvin double bridge measures low valued resistances using four-terminal resistors, matching option (B).

Let's summarize:

The Kelvin double bridge exists to remove lead and contact resistance error in low-resistance measurement.
Four-terminal resistors, with separate current and potential terminals, are what makes that error cancellation possible.
High resistances are measured by other methods where lead resistance is not a significant source of error.

So the blanks are filled as "low" and "four-terminal", option (B).