In the previous sections, you studied what power is and tried a few sample calculations. In this section, you will look at how power is related to series and parallel circuits.

The following simulation allows you to build your own circuit and measure the current and voltage. Build the circuits shown, and answer the questions after each one.

Click to Run

Source: Circuit construction kit dc, The University of Colorado – physics

Series Circuit:

In the Tools box, click on Voltmeter and click on Non-Contact Ammeter. Construct the series circuit shown in the figure below. (Your circuit does not have to look exactly like the figure below, but should be similar.)

Source: Circuit construction kit dc, The University of Colorado – physics

Click play to start the animation. To measure a voltage, use your mouse to place the red and black probes from the voltmeter on either side of an object in the circuit. To measure current, drag the ammeter so that the crosshairs are over a wire.

1. What is the current in the circuit?

   Interactive popup. Assistance may be required.

   Check Your Answer

   I = 0.45 A

2. What is the voltage of the battery?

   Interactive popup. Assistance may be required.

   Check Your Answer

   9 V

3. Calculate the power provided by the battery.

   Interactive popup. Assistance may be required.

   Check Your Answer

   P = IV
   P = (0.45 A) (9 V)
   P = 4.05 W

4. What is the voltage drop across each light bulb?

   Interactive popup. Assistance may be required.

   Check Your Answer

   Each bulb has a voltage drop of 4.5 V.

5. Calculate the power dissipated by each light bulb.

   Interactive popup. Assistance may be required.

   Check Your Answer

   P = IV
   P = (0.45 A) (4.5 V)
   P = 2.025 W

6. How does the power provided by the battery compare to the total power dissipated by the light bulbs?

   Interactive popup. Assistance may be required.

   Check Your Answer

   Battery: 4.05 W
   Bulbs: 2.025 W + 2.025 W = 4.05 W
   They are the same.

Parallel Circuit:

In the Tools box, click on Voltmeter and click on Non-Contact Ammeter. Construct the parallel circuit shown in the figure below. (Your circuit does not have to look exactly like the figure below, but should be similar.)

Source: Circuit construction kit dc, The University of Colorado – physics

Click play to start the animation. To measure a voltage, use your mouse to place the red and black probes from the voltmeter on either side of an object in the circuit. To measure current, drag the ammeter so that the crosshairs are over a wire.

1. What is the current in each branch of the circuit?

   Interactive popup. Assistance may be required.

   Check Your Answer

   Current through battery: 1.8 A
   Current through bulb 1: 0.9 A
   Current through bulb 2: 0.9 A

2. What is the voltage of the battery?

   Interactive popup. Assistance may be required.

   Check Your Answer

   9 V

3. Calculate the power provided by the battery.

   Interactive popup. Assistance may be required.

   Check Your Answer

   P = IV
   P = (1.8 A) (9 V)
   P = 16.2 W

4. What is the voltage drop across each light bulb?

   Interactive popup. Assistance may be required.

   Check Your Answer

   9 V

5. Calculate the power dissipated by each light bulb.

   Interactive popup. Assistance may be required.

   Check Your Answer

   P = IV
   P = (0.9 A) (9 V)
   P = 8.1 W
   It is the same for each bulb.

6. How does the power provided by the battery compare to the total power dissipated by the light bulbs?

   Interactive popup. Assistance may be required.

   Check Your Answer

   Battery: 16.2 W
   Bulbs: 8.1 W + 8.1 W = 16.2 W
   They are the same.