Introduction:

Light bulbs connected in series behave differently than light bulbs connected in parallel. This can be demonstrated by using the same power source to connect light bulbs in series and light bulbs in parallel. The light bulbs in parallel have a brighter glow. How do resistors in parallel behave? How is the current divided among resistors in parallel?

Practice:

Procedure:

Construct a simple parallel circuit.

1. Open the Toolbar and select a DC power supply, a 150-ohm resistor, an ammeter, and three wires.

2. Observe the DC power supply light to make sure the power is turned off.

3. Connect the components as shown in the following circuit diagram. Make sure the ammeter is connected properly.

4. Double-click on the DC power supply to open its Property Box, and set the voltage to 9 volts. Turn on the DC power supply. Observe and record the reading on the ammeter. Note: Several ammeters will be added to this circuit. Make sure each ammeter is set to the 0-1A range, so the readings are consistent.

5. Turn off the power supply.

6. Open the Toolbar and select an additional 150-ohm resistor, another ammeter, and three wires. Form a simple parallel circuit with two resistors by connecting the 150-ohm resistor and the ammeter to the original circuit, as shown in the following diagram.

7. Turn on the power supply. Observe and record the ammeter readings.

8. Turn off the power supply.

9. Open the Toolbar and select two more ammeters and two wires. Connect them to the circuit so they measure the current flow before and after it leaves the resistors.

10. Turn on the power supply and observe the meter readings.

11. Replace the top resistor with a 470-ohm resistor.

12. Observe the meter readings.

13. Open the Toolbar and select a voltmeter and two wires. Connect the voltmeter in parallel with the resistors. Measure the voltage across the resistors.

14. Turn off the power supply and replace the 470-ohm resistor with a 100-ohm resistor.

15. Turn on the DC power supply. Observe and record the ammeter readings.

To answer the questions pertaining to this experiment, click on the Questions button.

EXPERIMENT 4: Parallel Circuits with Resistors/Practice

Questions:

Select the best answer or the answer closest to your calculated value.

1. When a second resistor with equal resistance value is added in parallel to the first one, the current flowing through the first resistor
a) doubles
b) is cut in half
c) remains the same
d) is zero

2. After adding the second resistor to the circuit, the current coming from the DC power supply
a) doubles
b) is cut in half
c) remains the same
d) is zero

3. The current before entering the resistors is
a) lower than the current after exiting the resistors
b) higher than the current after exiting the resistors
c) zero
d) the same as the current after exiting the resistors

4. The sum of the currents flowing through both 150-ohm resistors is
a) lower than the current after exiting the resistors
b) higher than the current after exiting the resistors
c) lower than the current before entering the resistors
d) the same as the current before and after passing through the resistors

5. The current flowing through the 470-ohm resistor is
a) lower than the current flowing through the 150-ohm resistor
b) higher than the current flowing through the 150-ohm resistor
c) zero
d) the same as the current flowing through the 150-ohm resistor

6. The sum of the currents flowing through the 150-ohm and the 470-ohm resistors is
a) lower than the current after exiting the resistors
b) higher than the current after exiting the resistors
c) lower than the current before entering the resistors
d) the same as the current before and after the resistors

7. The voltage drop across the 470-ohm resistor is
a) lower than the voltage drop across the 150-ohm resistor
b) higher than the voltage drop across the 150-ohm resistor
c) zero
d) the same as the voltage drop across the 150-ohm resistor

8. The current flowing through the 100-ohm resistor before it burns out is
a) lower than the current flowing through the 150-ohm resistor
b) higher than the current flowing through the 150-ohm resistor
c) zero
d) the same as the current flowing through the 150-ohm resistor

9. The sum of the currents flowing through the 150-ohm and 100-ohm resistors is
a) lower than the current after exiting the resistors
b) higher than the current after exiting the resistors
c) lower than the current before entering the resistors
d) the same as the current before and after passing through the resistors

10. The voltage drop across the 100-ohm resistor is
a) lower than the voltage drop across the 150-ohm resistor
b) higher than the voltage drop across the 150-ohm resistor
c) zero
d) the same as the voltage drop across the 150-ohm resistor

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