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Current Electricity

Question
CBSEENPH12037490

Determine the equivalent resistance of networks shown in the figures (a) and (b) below.


Solution
a) Equivalent resistance of network in fig. (a)

The given network is a series combination of four identical units.
Let us consider one such unit as shown in fig. One such unit is equivalent to a parallel combination of 2 Ω and 4 Ω.

Its equivalent resistance is 

Rp = 2×42+4Ω = 86Ω = 43Ω

So, one unit of the given electrical network is a series combination of four resistors, each equal to 43Ω.

Thus, the combined resistance is 4× 43
163Ω163Ω or 5.33 Ω 

=
163Ω= 5.33 Ω.

b) Equivalent resistance of network in fig (b) 

Suppose a battery is connected between A and B. Same current will flow through all the resistors. So, all the resistors are connected in series.

∴ Equivalent resistance,
Rs = R + R + R + R + R = 5R

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