Diopters homework problem

[lostfan176]

Homework Statement

A prescription for a corrective lens calls for +1.50 diopters. The lensmaker grinds the lens from a "blank" with n = 1.46 and a preformed convex front surface of radius of curvature of 19.0 cm. What should be the radius of curvature of the other surface?

Homework Equations

$$\frac{1}{f} = (n-1)\left ( \frac{1}{R_1} - \frac{1}{ R_2} \right )$$

The Attempt at a Solution

1.5=(1.46 - 1)(1/19 - 1/x)

(1.5/.46) - 1/19 = 3.208
-1/3.208 = -.3117

which is wrong
am i doing this right cause i don't think i am

 

[alphysicist]

Hi lostfan176,

One thing I see: the value in diopters of a lens is the inverse of the focal length in meters. When you wrote 1/f=1.5, you chose your units of length in meters, but then you wrote R1 in centimeters.

 

[Moetasim]

I am unable to provide direct solutions to homework problems. However, I can help guide you through the problem-solving process.

Firstly, let's clarify the given information. The prescription for the corrective lens calls for a power of +1.50 diopters. This means that the lens needs to have a focal length of 1/1.50 meters, which is approximately 0.67 meters. The lens is being made from a blank with a refractive index of 1.46. The front surface of the lens has already been preformed with a convex shape and a radius of curvature of 19.0 cm. We are trying to determine the radius of curvature for the other surface.

Now, let's use the given equation: 1/f = (n-1)(1/R1 - 1/R2). Rearranging this equation, we get 1/R2 = (n-1)(1/f - 1/R1).

Substituting the given values, we get 1/R2 = (1.46-1)(1/0.67 - 1/0.19). Solving this, we get 1/R2 = 3.208.

Finally, we can calculate the radius of curvature for the other surface by taking the reciprocal of 3.208, which gives us the value of approximately 0.3117 meters or 31.17 cm.

I hope this helps you in solving the problem. Remember to always double-check your calculations and units to ensure accuracy.