When the switch 1 is closed, the current through the `8 Omega` resistance is `0.75A`. When the switch 2 is closed (only), the current through the resistance marked x is 1 A. The value of x is

Options

A. 5 V
B. 18 V
C. 10 V
D. 15 V

Answer

B

Explanation

b. When switch (1) is closed

`I_1 = I (4/(4+12)) or 3/4 = I(1/4)`
`I = 3A`
When switch (2) is closed the current through resistance x is
1 A. hence
`V_(AB) = 1 xx ((4 xx 12)/(4+12)) or V_(AB) = 3V`
hence potential difference across x will be 3 V.
`x = 3/7 = 3 Omega`
Hence `epsilon = 3(3+3) = 18V` .