IF
A resistance R connected in series with
parallel combination OF two resistance
and 8 ohm. Calculate R if the power
dissipated is 70 W when the applied
voltage
is 20 V
V across
the circuit.
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The value of the resistance R in figure is adjusted such that power dissipated in the 2 Ω resistor is maximum. Under this condition
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Correct option is
A
R=0
C
power dissipated in the 2 Ω resistor is 72 W
The power dissipated in circuit is given by
P=
R
V
2
For the resistances in parallel the equivalent resistance is less than smallest resistance in combination of resistors hence power dissipation is maximum in this case.
For the resistances in series the equivalent resistance is addition of resistors hence power dissipation is minimum in this case.
Hence, to avoid maximum power dissipation in parallel circuit R must be equal to zero so the equivalent of parallel resistors will be
R
p
=
8+0
(0)(8)
=0Ω
Since, R
p
=0Ω voltage across it is zero.
Therefore power dissipated in 2Ω resistor is
P=
R
V
2
P=
2
(12)
2
P=72W
Explanation: