Question

A torch bulbs is rated at `2.5 V and 750 mA`. Calculate its
(i) power
(ii) its resistance and
(iii) the energy consumed if the bulb is lighted for `4 hour`.

Answer 1

Here, `V = 2.5 V, I = 750 mA = 750 xx 10^-3 A = 0.75 A`
time for which the bulbs is lighted, `t = 4 hour`
(i) power of the bulb, `P = VI = (2.5 V)(0.75 A) = 1.875 W`
(ii) resistance of the bulbs, `R = (V)/(I) = (2.5 V)/(0.75) = 3.32 Omega`
(iii) energy consumed by the bulb in `4 hour` i.e.,
`W = P t = (1.875 W)(4 h) = 7.5 Wh = (7.5 W) (3600 s)`
=`27000 j` `(1 W = 1 J//s)`.