Question

Two resistors is series draw a 5 ampere from a 30V source. If the value of the second resistor is doubled, the current drops to 3 ampere. Determine the resistances.

Answer 1

let the two resisters be A and B

V is 30 volta, current is 5 Ampere in case 1

V =IR

30=5×(A+B)

A+B=6

A=6-B(equation 1)

Case 2

Here let the resisters be A and 2B( according to question).

Current draw is 3 Ampere

V=30volts

V =IR

30=3×(A+2B)

10=A+2B(equation 2)

From equation 1 and 2

A=6-B

10=A+2B

so,

10=6-B+2B(from 1 and 2)

6+B=10

B=4(equation 3)

A=6-B(from equation 1)

A=6-4(from equation 1 and 3)

Hence A =2 ,B=4.