WEBVTT
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This is College Physics Answers
with Shaun Dychko.
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This person needs to have
the power of their eye
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decreased by 9.00 diopters
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and the percent error in this surgery that
does this correction is 5.0 percent
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so the question in part (a) is
what power of
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glasses could the person possibly need
after the procedure
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considering the amount of
air that's involved?
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So this is the maximum power of glasses;
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this is not the maximum
power of their eye
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because normal vision is
a power of 50.0 diopters
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but this is just the amount in excess of
50 that might occur
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and it's the amount that the glasses
need to correct
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to get to the normal vision of
50.0 diopters.
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So the maximum amount by which
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their power of their eye will be
above normal
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is the initial 9.00 diopters that it has
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because that's the goal is to decrease
the power by 9.00 diopters
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that means their power must be
9.00 diopters too much.
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So they will have 9.00 diopters
to begin with
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plus the smallest change
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or in other words, a decrease in
9.00 diopters
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multiplied by 95 percent because this is
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9.00 diopters minus 5.0 percent.
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This works out to 0.45 diopters could be
the final amount by which
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their sight is too powerful
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or the minimum power
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this is the amount below normal will be
the 9.00 diopters
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plus the maximum possible decrease
after the procedure
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and so that's 9.00 diopters plus
the 9.00 diopter decrease
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times 1.05 so this is the maximum possible
decrease within the error given
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and that is negative 0.45 diopters.
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So the final power needed from the glasses
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is negative 0.45 diopters up to
positive 0.45 diopters.
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Then part (b) asks was this person
near-sighted or far-sighted initially
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and they were myopic and the word 'myopic'
means near-sighted
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so they can see near and cannot see far.