In
the circuit in figure 1 below, find the value of supply voltage V so that the
20Ω resistor can dissipate 180W.
Solution
I4²
x 20 = 180W
x 20 = 180W
I4
= 3A
= 3A
Since 15Ω and
20Ω resistances are in parallel,
20Ω resistances are in parallel,
I3
x 15 = 3 x 20
x 15 = 3 x 20
I3
= 4A.
= 4A.
I2
= I3 + I4 = 4 + 3 = 7A.
= I3 + I4 = 4 + 3 = 7A.
Now,
resistance of the circuit to the right of point A
resistance of the circuit to the right of point A
= 10 +
[15||20] =18.57Ω
[15||20] =18.57Ω
I1
x 25 = 7 x 18.57
x 25 = 7 x 18.57
I1
= 5.2A.
= 5.2A.
I = I1+I2
= 5.2 + 7 = 12.2A
= 5.2 + 7 = 12.2A
Total circuit
resistance
resistance
= 5 +
[25||18.57] = 15.66Ω
[25||18.57] = 15.66Ω
V = IR
= 12.2 x
15.66 = 191V.
15.66 = 191V.
