Q)
(chatquestion)...nce.
R R
R, R
[3.83(a)]
This last equation relating the four resistors is called the balance
adition for the galvanometer to give zero or null deflection.
The Wheatstone bridge and its balance condition provide a practical
thod for determination of an unknown resistance. Let us suppose we
re an unknown resistance, which we insert in the fourth arm; R is
at known. Keeping known resistances R, and R, in the first and
d arm of the bridge, we go on varying R, till the galvanometer shows
l delection. The bridge then is balanced. and from the balance
ition the value of the unknown resistance R, is given by,
R
R, =R,
[3.83(b)
R
A practical device using this principle is called the meter bridge.
be discussed in the next section.
Example 3.8 The four arms of a Wheatstone bridge (Fig. 3.26) have
the following resistances:
AB = 1002, BC = 102, CD = 52, and DA = 602.
1-I
1000
109
152
602
I+I,
10V
FIGURE 3.26
...
