Teaching Physics with the Physics Suite

Edward F. Redish

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A battery and two bulbs

Consider the two arrangements of batteries and bulbs shown at the right.

All four bulbs are identical and have resistance R. The two batteries are identical and maintain a potential difference (EMF) = E. Answer the following questions and explain why you believe your answer. (Most bulbs are brighter when there is more current through them. Assume that is the case for these bulbs.)

  1. In system 1, which bulb is brighter?
  2. In system 1, what is the current through each bulb, the voltage drop across each bulb, and the power dissipated by each bulb?
  3. In system 2, which bulb is brighter?
  4. In system 2, what is the current through each bulb, the voltage drop across each bulb, and the power dissipated by each bulb?
  5. Which bulbs are brighter, those in system 1 or those in system 2?
  6. If one bulb in each system burns out, will the other go out as well? Why? If the other bulb doesn't go out will it get brighter or stay the same when the first bulb in the circuit burns out?

Note to the instructor: Students have well documented difficulties with simple battery and bulb circuits. Many bring an undifferentiated concept of "electricity" to class, failing to distinguish between voltage (pressure) and current (flow). This example, and other related ones bring this out.

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Page last modified October 16, 2002: E06