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AP Physics B Current Electricity “Virtual Power Activity”
go to http://phet.colorado.edu Choose the “Circuit Construction Kit”
Part I-Bulbs in series
Build a series circuit with one bulb, a switch, connecting wires, and a voltage source. Observe what happens when you
close the switch briefly. Pay attention to the relative brightness of the bulb.
1. Predict what will happen to the brightness of the bulbs when you add another bulb in series. How will their
brightness compare to the first bulb? Why?
2. How will their brightness compare to each other? Try it, and record your observation below.
3. Then add a third bulb, also in series, and record your observation below. Explain.
4. Show dimensional analysis for this equation in fundamental units (m, kg, s). What is it equivalent to?
P  IV
Record the Voltage, Current, and Power values for each bulb in the series circuit in the table below

Bulb
1.
Voltage (V)
I (A)
P (W)
2.
3.
Sketch the circuit in schematic below, numbering the bulbs.
5. Write an equation for the voltages in this circuit.
Part II-Bulbs in parallel
Build a parallel circuit with two bulbs, a switch, connecting wires, and a voltage source. Before closing the switch,
predict the brightness.
7. Compare the brightness of the bulbs in this circuit with the series circuit above. Explain what is happening.
Add a third bulb in parallel and a switch, so that you can compare the brightness between two parallel bulbs and three
parallel bulbs by closing the switch.
8. What happens when you throw the switch, allowing the third bulb to light? Explain. Hint: Add an ammeter so you
can see what happens to current when you add another bulb.
Record the Voltage, Current, and Power values for each bulb in the parallel circuit in the table below
Bulb
1.
Voltage (V)
I (A)
P (W)
2.
3.
Sketch this circuit in schematic below, numbering the bulbs.
9. Write an equation for the currents (going into the first junction and coming out of the last junction).
Part III-Bulbs in series and parallel
Build a series-parallel circuit with three bulbs, two in parallel with each other, one in series with the parallel branch.
Sketch a schematic of the circuit below. Label each bulb with a number, 1-3.
11. Compare the relative brightness of each of the three bulbs before you begin.
Record the Voltage, Current, and Power values for each bulb in the series-parallel circuit in the table below
Bulb
1.
Voltage (V)
I (A)
P (W)
2.
3.
12. Compare the brightness of the bulbs in this circuit with the parallel circuit above. Explain what is happening.