Calculating Watts

Watt Watt Watt?!?!

A watt is the basic unit of power. Power is the rate at which electrical energy is delivered to a circuit. “How many watts?” is a question often asked about speakers, sound systems, hair dryers, and light bulbs.

OHMMMMM….

• Ohms law states that voltage is the product of current and resistance. If you know two of the values, you can calculate the third.

• The power formula is related to Ohms law. Use the power formula to calculate the current flow when a lamp is on.

• The power formula is stated as:

P=E(I)

Where,

P=Power in Watts (W)E=Operating VoltageI=Current in amperes

What is the power for a light bulb with a voltage of 12.6 V and a current of 1.04 A?

P=E(I)P=12.6V(1.04A)=13.1W

Round the wattage to tenths, voltage to tenths, and current to hundredths.

Rewrite the power formula in terms of the current. Solve for I.

Start with P=E(I)Divide both sides by E.

P/E=E(I)/EI=P/E

Calculate the current in a bulb where the voltage is 14.5V and the power is 4.9W:

I=P/E(4.9W)/(14.5V)=0.34A

A 1154 bulb has a double filament. The operating voltage is 6.4 V and the currents are 2.63 A and 0.75 A?

What are the power values for each filament?

For the lower-current filament:P=E(I)=6.4V(0.75A)=4.8W

For the higher-current filament:P=E(I)=6.4V(2.63A)=16.8W

Don’t Get Frustrated!