An electric bulb taking in a current 0.25 A works on electric mains of pd 240 V Calculate the power of the bulb.
Answers
Energy (power×time) is measured in Joules and by including time (t) in the power formulae, the energy dissipated by a component or circuit can be calculated.
Energy dissipated = Pt or VI×tasP=VI.
In the question, it is given that the current I is 0.5 A and voltage V is 4 V. Thus the power dissipated is calculated as P=VI=4V×0.5A=2W.
Substituting V=IR (Ohm's law) in the above formula, we get, P=I ² ×R.
Therefore, the total resistance in the circuit is calculated using the relation R= I²P = 0.5 ²2 =8ohms.
The internal resistance of the cell is 2.5 ohms, hence, the resistance of the bulb is 8−2.5=5.5 ohms.
The power dissipated by the bulb in 10 minutes is calculated from the formula P=I²×R×t, where I=0.5A,R=5.5 ohms and t=10 minutes, that is 600 seconds.
Hence, P=0.5
2 ×5.5×600=825J.