Bukhovtsev-et-al-Problems-in-Elementary-Physics

416
ANSWERS AND SOLUTIONS
Therefore.
1 1 1 1 1
-=-+-=---
03 al to at at
and aa=15 em
757. The long-sighted man when wearing his friend's spectacles can see
only very far objects. Therefore, the distance a 2 of best vision of the eye of
the long-sighted man can be determined from the equation
1 1
---=D
at at 1
where al is a very great distance (a1 -+ 00) and D} is the optical power of
the spectacles of the short-sighted man.
The optical power D 2 of the spectacles that correct the defect of vision of
the long-sighted man can be found from the formula
1 1
---=D ao
2 a2
where a o = O.25 metre is the distance of best vision of the normal eye.
The distance a3 of best vision of a short-sighted eye can be found from the
equation
1 1
---=D
ao aa 1
If the short-sighted man wears the spectacles of his long-sighted friend,
the distance of best vision, Le., the minimum distance a at which the shortsighted
man can easily read a small type, can be determined from the formula
1 1
---=D a aa 2
Upon solving these four equations, we get a= 12.5 ern.
758. When an object with a height of 1 is examined from a distance of D,
the angle of vision q>l is determined by the formula
I