Question

6.An electric iron has a rating of 750W,220V.Calculate:(a)current passing through it and (b)Its resistance when in use.
7.Two lamps,one rated 100W,220V and other 40W ,220V are connected in parallel to 220V mains supply.Calculate the current drawn from the supply line.
8.An electric lamp is marked 100W,220V.Its used for 5hrs daily (a)Its resistance when in use. (b)Energy consumed in kWh per day.

Answer 1

The equation for electrical power is\[P = VI\]where V is the voltage and I is the current. This can be rearranged to solve for I in 6(a).

6(b) can be solved with Ohm's Law\[V=IR\]or if you'd like, from power, after substituting Ohm's law in for I\[P = {V^2 \over R}\]

For 7, realize that because they are in parallel, their voltages are the same.
We can find the resistance of each lamp from\[P = {V^2 \over R}\]Then the equivalent resistance as\[{1 \over R^*} = {1 \over R_1} + {1 \over R_2}\]Then the total power as\[P_t = {V^2 \over R^*}\]However, this will reveal that (with a bit of algebra)\[P_t = P_1 + P_2\]

For 8, again the resistance can be found as\[P = {V^2 \over R}\]The energy usage is simply\[E = P \cdot t\]

Answer 2

thank you so much, eashmore , for your guidance.