Carey Foster Bridge

Howdy Friends, this post gives data about Carey Foster bridge. We will likewise figure out how this bridge can be utilized to decide the opposition in detail with inferring an articulation for deciding obstruction.

Carey-Foster bridge Experiment

We have just observed some essential strategies for estimating medium protections. Carey foster bridge is the strategy utilized for estimation of medium opposition. Carey foster bridge is exceptionally utilized for the correlation of two equivalent protections. The circuit for Carey-Foster Bridge is appeared in the figure beneath. A slide wire having length L is incorporated among R and S. opposition P and Q are balanced with the goal that the proportion P/Q is around equivalent to R/S. this can be accomplished by sliding contact on slide wire.

Carey Foster Bridge: Working Principle

The working guideline of the Carey Foster bridge is like the Wheatstone bridge. The potential fall is specifically relative to the length of the wire. This potential fall is almost equivalent to the potential fall over the obstruction associated in parallel to the battery.


Let l1 be the separation of the sliding contact from the left-hand end of the slide-wire of Carey foster bridge. The opposition R and S are exchanged and balance is again acquired. Let the separation is currently l2.

Let r= resistance/unit length of slide wire

For first balance,

Carey foster bridge method 1

For second balance,

Carey foster bridge method 2


Carey foster bridge method 3

Where l1 and l2 are adjusted focuses when slide wire is aligned by shunting S with a known opposition and S’ is the estimation of S when it is shunted by a known obstruction. In this way Carey foster bridge can be utilized to quantify the medium opposition.

Some Importance Quetion-answer About Carey Foster Bridge

Q. What is obstruction?

A. Resistance R=V \ I, where V is the potential contrast connected over the wire and I is the present coursing through it because of the potential distinction.

Q.What is explicit opposition?

A. The particular opposition of a material is the obstruction of the one-centimeter length of wire whose cross-sectional region is one square centimeter.

Q. What is the impact of temperature on opposition?

A. Opposition increments with increment in temperature of the material of wire.

Q.In what materials the opposition diminishes with increment in temperature?

A.In Semiconductors

Q. In the event that the span of wire is multiplied will the particular opposition change?

A. Explicit obstruction is free of length or range of wire it just relies upon the material of the wire.

Q.Why is the obstruction wire multiplied before twisting over the bobbin?

A. To stay away from the inductive impacts. The course of current in one wire is inverse to the next consequently the all out transition is constantly zero.

Q.What is the standard of Carey Foster Bridge?

A. The situation of invalid point changes on the wire when the opposition is associated in the external holes is traded. The distinction in the estimation of opposition is equivalent to the obstruction of the contrasts between bridge wire i.e (L-l).

Q.What is the standard of Wheatstone Bridge?

A. At the point when the four protections P, Q, R, S in the four arms of the Wheatstone bridge are to such an extent that there is no redirection in the galvanometer, we have:


Q.When is Carey Foster Bridge generally touchy?

A. It is most touchy when P, Q, R, S are the equivalent or of a similar request.

Q.Why the obstruction for inward proportion arms be equivalent?

A.For expanded affectability and precision.

Q.What is the base contrast in protections that can be estimated via Carey Foster Bridge?

A.The obstruction of one-millimeter length of the bridge wire.

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