Problem regarding lenses

1. The problem statement, all variables and given/known data
Which of the following is a characteristic of a farsighted person (nearby objects appear blurry)?
a)the minimum focal length they can get for the lens of their eye is not small enough.
b) the maximum focal length they can get for the lens of their eye is not large enough
c) their lens of their eye is not symmetrical

2. Relevant equations
1/f = 1/p + 1/q

f = 1/(1/p + 1/q)

p = 1/(1/f-1/q)

f is focal length, p is object distance, q is image distance
3. The attempt at a solution

The answer is B. I agree, but I don’t understand my professor’s explanation.

The explanation for B being correct:
"with q fixed, then to make p small f –> large. If can’t get f –> large then can’t get p –> small."

My reasoning – I found that when P increases, F must increase, which is the opposite of the explanation. If when P decreases F decreases, and if when P is small the objects are blurry, F must be too small.

If someone can confirm or deny the validity of my reasoning and explain the explanation given by my professor it would be much appreciated.

http://ift.tt/QNghbp

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