Respuesta :
Answer:
Explanation:
Far point = 17 cm . That means he can not see beyond this distance .
He wants to see at an object at 65 cm away . That means object placed at 65 has image at 17 cm by concave lens . Using lens formula
1 / v - 1 / u = 1 / f
1 / - 17 - 1 / - 65 = 1 / f
= 1 / 65 - 1 / 17
= - .0434 = 1 / f
power = - 100 / f
= - 100 x .0434
= - 4.34 D .
Refractive power is the measure of degree of convergence by a lens. The required refractive power for the given glasses is -4. 34 D.
Using lens formula
[tex]\bold { \dfrac 1 v - \dfrac1 u = \dfrac {1}f}[/tex]
Where,
f- focal point
v - distance of the image
u - distance of the object
So,
[tex]\bold { \dfrac 1 {-17} - \dfrac1 {-65} = \dfrac {1}f}\\\\\bold { 0.434 = \dfrac {1}f}\\[/tex]
Since, [tex]\bold {power = \dfrac {- 100 }f}[/tex]
So,
[tex]\bold { power = - 100 \times 0.0434}}\\\\\bold { power = - 4.34\ D}[/tex]
Therefore, the required refractive power for the given glasses is -4. 34 D.
To know more about refractive power,
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