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QUESTION: I have attached the question as an image, could you please explain why the answer is b as I thought it was c

ANSWER: No, just the opposite.  Obviously, setup 1 has two light bulbs in parallel across the same voltage and will be twice as bright as setup 3.  The most resistance in the circuit is in setup 2.  That would reduce the current in the bulbs.  Now, since light bulbs are quite non-linear you can't say with perfect certainty that 2 would be that much less bright than setup 3...but assuming a fairly consistent resistance in the bulbs you can say it would probably be a good bit less bright.  The power dissipated by a resistor depends on the square of the current in it.  If you have ~half the current (~twice the resistance), then you end up with ~half the emitted power.  P=(I^2)*R

---------- FOLLOW-UP ----------

QUESTION: So does that mean that current would be higher if two light bulbs were to be placed in parallel rather than series

Of course.  Voltage determines the current.  Look at the parallel circuit, there's 9V across each bulb.  In series, there's half that across each, adding up to 9V (opposite direction but same magnitude as the battery, the sum of voltages around a closed loop is always zero).


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Dr. Stephen O. Nelson


I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.


I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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