Q) a battery of e.m.f. 15v and internal resistance 2 ohm is connected to two resistors of 4 ohm and 6 ohm joined(a)in series (b)in parallel. find in each case the electrical energy spent per minute in 6 ohm resistor.
Sol) (a) In series
R = 2+4+6 = 12 ohms
so I = V/R = 15/12 = 5/4 = 1.25 A
so power consumed by 6 ohm resistor = I2 r = 1.25 2 x 6 = 9.375 Watt
so Energy spent in 1 min or 60s = 9.375 x 60 = 562.5 J
(b) for parallel
in 4 and 6 ohm are in parallel then R = 24/10 = 2.4
which is in series with internal resistance of 2 ohm
so Reff = 4.4 ohm
I = 15/4.4
so energy spent in 60s = 60 x I2 Reff
Moderation Team
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