In figure circuit section `AB` absorbs energy at the rate of `5.0 W` when a current` i =1.0A` passes through it in the indicated direction.
(a) What is the potential difference between points `A` and `B`?
(b) Emf device `X` does not have internal resistance. What is its emf?
(c) What is its polarity (the orientation of its positive and negative terminals)?

Options

A. `10 V`
B. `50 V`
C. `20 V`
D. `30 V`

Answer

B

Explanation

As section `AB` consumes `50 W at 1 A and P = VI`. S0
`V = V_(A) - V_(B) = (P)/(I) = (50)/(1) (W)/(A) = 50 V`
As `R and C` are in series,
`V = V_(R) + V_( C ) or V_( C ) = V - V_(R )`
But here `V = 50 V and V_(R) = IR = 1 xx 2 = 2 V`. So `V_( C ) = 50 - 2 = 48 V`.
Now as the element `C` absorbs energy and has no resistance , it is a source of emf with zero internal resistance ( i.e., ideal battery ). So emf
is `E = V + Ir = 48 + 1 xx 0 = 48 V`.
As in charging , positive and negative terminals of the charger are connected to the positive and negative terminals of the battery, respectively ,` B` is connected to the negative terminal of element `C`.