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1. (a) If the human eyeball is 4cm from lens to retina, what is the range of the power and focal length of the eye lens when focussing an object an infinite distance away and one at the normal near point 25cm away?

(b) A long-sighted person(whose eyeball length is still 4cm)has a near point of 2m. What is the power of the eye lens when focussing at the near point?

What power glasses lens would the person need to correct their near point back to 25cm?

Any help will greatly be appreciated!