Understanding Current in a 60W Incandescent Bulb at 240V
This question asks us to find the electric current drawn by a 60 W incandescent bulb when connected to a standard domestic electrical supply voltage of 240 V. This is a common calculation involving the relationship between power, voltage, and current in an electrical circuit.
Given Information
- Power rating of the incandescent bulb (P) = 60 W
- Voltage of the domestic supply (V) = 240 V
Required to Find
- Current (I) flowing through the incandescent bulb.
Relationship Between Power, Voltage, and Current
The electrical power (P) consumed by an appliance is related to the voltage (V) across it and the current (I) flowing through it by the formula:
\(P = V \times I\)
To find the current (I), we can rearrange this formula:
\(I = \frac{P}{V}\)
Calculating the Current
Now, we can substitute the given values for power (P) and voltage (V) into the rearranged formula:
\(I = \frac{60 \text{ W}}{240 \text{ V}}\)
\(I = \frac{60}{240} \text{ A}\)
\(I = \frac{1}{4} \text{ A}\)
\(I = 0.25 \text{ A}\)
Therefore, the current required to light the 60 W incandescent bulb in a 240 V domestic supply is 0.25 A.
Summary of Calculation
| Quantity | Symbol | Value | Unit |
|---|---|---|---|
| Power | P | 60 | W |
| Voltage | V | 240 | V |
| Current | I | 0.25 | A |
This calculation shows that a 60 W bulb operating at 240 V draws a current of 0.25 A.
Revision Table: Electrical Formulas
| Formula | Description | Variables |
|---|---|---|
| \(P = V \times I\) | Power equals Voltage times Current | P = Power, V = Voltage, I = Current |
| \(V = I \times R\) (Ohm's Law) | Voltage equals Current times Resistance | V = Voltage, I = Current, R = Resistance |
| \(P = I^2 \times R\) | Power equals Current squared times Resistance | P = Power, I = Current, R = Resistance |
| \(P = \frac{V^2}{R}\) | Power equals Voltage squared divided by Resistance | P = Power, V = Voltage, R = Resistance |
Additional Information: Incandescent Bulbs and Power Consumption
Incandescent bulbs work by heating a filament until it glows. The power rating (like 60 W) indicates how much electrical energy the bulb converts into light and heat per second when operated at its intended voltage (in this case, 240 V). The current drawn is directly proportional to the power for a given voltage.
For example, a 100 W bulb at the same 240 V would draw a higher current:
\(I = \frac{100 \text{ W}}{240 \text{ V}} \approx 0.417 \text{ A}\)
This is why higher wattage appliances draw more current from the supply.
The resistance of the filament in an incandescent bulb is not constant; it increases significantly as the filament heats up. The power rating is typically given for the bulb operating at its normal temperature and voltage.
Important Questions from Power in Electric Circuits
Which one of the following terms cannot represent electrical power in a circuit?
An electric bulb is connected to 220 V generator. The current drawn is 600 mA. What is the power of the bulb?
Which one of the following formulas does not represent electrical power?
In an electric circuit, a wire of resistance 10 Ω is used. If this wire is stretched to a length double of its original value, the current in the circuit would become :
One-kilowatt hour is equal to
