Question

Three identical bulbs $B_1$, $B_2$ and $B_3$ are connected as shown in figure. When all three bulbs glow, a current of 3 A is recorded by the Ammeter A.

How much power is dissipated in the circuit when all three bulbs glow together?

Answer 1

By the series and parallel combination concept find the current in each bulb thenUse the formula ${{P = VI}}$, Where P = power, I = current and V = potential difference and then substitute the given values of potential difference and current in the formula then evaluate power dissipation in the given circuit diagram.

Complete step by step solution:
Given: Bulbs B1, B2 and B3 are three identical
Current, I = 3 A
Potential difference, V = 4.5 V
To find: Power dissipation in the circuit when all three identical bulbs glows together
The rate at which electric energy is consumed is called power. It is denoted by P. SI unit of power is Watt.
From the given circuit diagram, it is clear that bulbs B1, B2 and B3 are connected in parallel combination.
Formula for power dissipation is given as ${{P = VI}}$
Where P = Power dissipated in the circuit
I = Current in the circuit
V = Potential drop across electric components (here bulbs)
On substituting the given values in above formula, we get
$\Rightarrow {{P = 4}}{{.5 \times 3 = 13}}{{.5 Watt}}$

Therefore, power of 13.5 W is dissipated in the circuit when all three bulbs glow together.

Note: Other formulae for power dissipation are ${{P = VI = }}{{{I}}^{{2}}}{{R = }}\dfrac{{{{{V}}^{{2}}}}}{{{R}}}$. On the basis of given quantities in the question, we can use different formulae. According to the question, values of voltage (V) and current (I) are given. So, we use formula P = VI. If in question, only the value of current and resistance is asked then we can use the formula ${{P = }}{{{I}}^{{2}}}{{R}}$. If in the question, only the value of voltage and resistance are given then we can use formula, ${{P = }}\dfrac{{{{{V}}^{{2}}}}}{{{R}}}$.
A watt hour and kilowatt hour are practical units of electric energy. The commercial unit of electric energy is kilowatt hour (kWh), where ${{1kWh = 1000Wh = 3}}{{.6 \times 1}}{{{0}}^{{6}}}{{J}}.$ Electric power is the rate at which electric energy is consumed. SI unit of electric power is Watt.