Electricity

YOU ARE LEARNING:

Power, Potential and Current

The power of a circuit is the rate at which energy is supplied. This can be calculated using the voltage, current and resistance of the circuit.

True or false? Energy can be created and destroyed.

So where does the energy come from in an electric circuit?

What do you think we call the energy transferred per second in an electrical circuit?

What do you think we measure power in?

A circuit has a power rating of 5 watts and is on for 5 seconds. The total energy transferred in this time is 25 joules. Which one of these formulas is correct?

Power is the rate of energy transfer in a circuit.

The rate is how many per second, so power is the energy per second, shown in this formula: $P=\frac{E}{t}$

We can rearrange this to make energy the subject so $E=P\times t$ .

Select the correct units for each variable:

You can select multiple answers

True or false? Work is done when the charge flows around the circuit.

The image shows a simple circuit of a battery and two resistors. Notice that the voltmeters are connected in series. This is to show the voltage at a particular point in the circuit, rather than the potential difference between two points.

The current has an initial potential difference of 6 V straight out of the battery.

After each of the resistors, the voltage _______________.

Do the resistors have the same potential difference?

Every time the charge goes through a component, energy is used up/lost.

This is why the voltage is less after each resistor.

If a charge of 2 coulombs travels through a component with a potential difference of 3 volts, the energy transferred is 6 joules. Which of the formulas below must be the correct formula for calculating the energy transferred?

Voltage or potential difference is the energy per charge in a circuit.

This definition of voltage gives us the formula $V=\frac{E}{Q}$ .

Making energy the subject, we get $E=Q\times V$ .

Select the correct units for each variable:

You can select multiple answers

The power of a circuit can also be affected by the potential difference and the current. If a circuit has a potential difference of 4 volts and a current of 3 amps, its power will be 12 W. So which of the following is the correct formula for power?

We know that $P=VI$ and that $V=IR$ . Imagine we want to calculate the power transfer in a circuit, but we only have the current and the resistance, not the potential difference. What does the formula look like that we can use?

We can calculate the power of a circuit multiple ways.

Out of the following options, which equations allow us to calculate the power of a circuit?

You can select multiple answers

Depending on the information given to you in a problem, certain equations will be more helpful than others.

It is useful to know how to use these equations to substitute into others, and find the right equation in terms of the variables you have.