Physics Review Question

Unit: Electricity
Year: 1997 Question#: 31
Question: To increase the brightness of a desk lamp, a student replaces a 60-watt light bulb with a 100-watt bulb. Compared to the 60-watt bulb, the 100-watt bulb has

(1 ) less resistance and draws more current
(2 ) less resistance and draws less current
(3 ) more resistance and draws more current
(4 ) more resistance and draws less current

What is this question really asking?




Explanation by: Raphael D

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Answer 1
less resistance and draws more current

CORRECT

This is the correct answer because by replacing the 60-watt bulb with a 100-watt bulb there would be less resistance and more current would be drawn. This would make the brightness of the desk lamp increase. This is really based on your understanding of Ohm's law,  V=IR

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Answer 2
less resistance and draws less current

INCORRECT

This answer is incorrect because less resistance does not go with less current. If the resistance is decreased current can only increase. Consult ohm's law, V=IR.  Remember that in this situation, V is constant.  It just doesn't make sense that the 100-watt bulb would have less resistance and draw more current. return to top

Answer 3
more resistance and draws more current

INCORRECT

This answer is incorrect because there cannot be an instance where there is a bulb that has more resistance and draws more current. More resistance always draws less current.  Consult ohm's law, V=IR.  Remember that in this situation, V is constant.  

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Answer 4
more resistance and draws less current

INCORRECT

This answer is incorrect because more resistance and less current would not increase the brightness of a desk lamp. More resistance does draw less current however it does not relate to this problem.  A brighter lamp means more power.  Since P=VI   I can't go down if P increased.

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What's this question really asking?

What is the relationship between resistance, current and increasing or decreasing the brightness of a lamp? return to top

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