Three lamps with 40 Ω, 30 Ω, and 15 Ω resistance are connected in parallel to a 90 volt circuit. What is the total current used by the three lamps?
A) 0.94 A

B) 15.25 A

C) 11.25 A

D) 1.06 A

Option C) 11.25 A

Explanation:

Given that:

Voltage V = 90 volts

total current I = ?

Three resistors each with 40 Ω, 30 Ω, and 15 Ω in parallel, the equivalent resistance of the combination (Rtotal) of the circuit is as follows:

i.e 1/Rtotal = (1/R1 + 1/R2 + 1/R3)

1/Rtotal = (1/40Ω + 1/30Ω + 1/15Ω)

1/Rtotal = (3 + 4 + 8)/120Ω

1/Rtotal = 15/120Ω

1/Rtotal = 1/8Ω

To get the value of Rtotal, cross multiply

Rtotal x 1 = 8Ω x 1

Rtotal = 8Ω

Then, apply the formula V = I x Rtotal

90 volts = I x 8Ω

I = 90 volts / 8Ω

I = 11.25 Amperes

Thus, the total current used by the three lamps is 11.25 Amperes