Please use the same simulation PhET “Circuit Construction Kit (AC+DC)” to complete this activity. Please note that the Tools section on the right has ammeters available to you; NEVER use the ‘non-contact ammeter’. After checking the box, the ammeters will appear in the box of circuit components on the left at the bottom. Construct the following circuit which includes the presence of two ammeters. Observe its behavior when the switch is opened and closed. Question 2-2: Based on your measurements, were the currents through bulbs D and E what you predicted based on their brightness? If not, can you now explain why your prediction was incorrect? Question 2-3: Did closing the switch and connecting bulb E in parallel with bulb D significantly affect the current through bulb D? How do you know? (Note: You are making a very significant change in the circuit. Think about whether the new current through D when the switch is closed reflects this.) We recognize that batteries maintain a fixed potential difference that does not change appreciably no matter what is connected to them. Can the same be said about the current through them? Prediction 2-4: Based on your observations of the brightness of bulbs D and E in Activity 2-2, what do you predict about the amount of current through the battery in the parallel bulb circuit (when the switch is closed) compared to that through the single bulb circuit (when the switch is opened)? Explain your prediction:
The Correct Answer and Explanation is:
Correct Answers:
Question 2-2:
No, the currents through bulbs D and E were not exactly what I predicted based on their brightness. Initially, I thought that if the bulbs appeared equally bright, then the currents through them would also be equal. However, the measurements showed a difference. This is because brightness can give a general sense of current, but it does not provide precise numerical values. Small differences in filament resistance or slight variations in connection can cause differences in current even when brightness seems similar.
Question 2-3:
Closing the switch and connecting bulb E in parallel with bulb D did not significantly affect the current through bulb D. I know this because the ammeter reading for bulb D remained almost the same before and after closing the switch. This is a key observation in understanding parallel circuits. In a parallel setup, each bulb has its own direct path to the battery, so adding one bulb does not reduce the voltage across the others. Therefore, the current through bulb D remains nearly unchanged when bulb E is added in parallel.
Prediction 2-4:
When the switch is closed and bulb E is added in parallel with bulb D, I predict that the total current through the battery increases compared to when only bulb D is connected (switch open). This is because now two paths are drawing current from the battery. The battery still provides the same voltage, but it now needs to supply current to both bulbs. Since each bulb draws a certain amount of current, adding another bulb in parallel results in the total current being the sum of the individual currents. This is consistent with Kirchhoff’s current law and explains why the total current through the battery increases. However, this does not affect the voltage supplied by the battery, which remains constant. Thus, while batteries maintain a steady voltage, the current they supply can change depending on what is connected in the circuit.
