Calculate Focal Length to Reduce Viewing Distance to 25cm

AI Thread Summary
To calculate the focal length of a converging lens needed to allow a patient to see objects at 25cm instead of 1m, the lensmaker's equation is applied. The initial attempt used the standard form of the equation but did not yield the correct result. The correct approach involves using the modified formula 1/u - 1/v = 1/f, where u is the object distance (1m) and v is the image distance (0.25m). The expected focal length is 33cm, indicating that the image formed is virtual. This calculation is crucial for aiding the patient's vision at closer distances.
v_pino
Messages
156
Reaction score
0

Homework Statement


A patient is unable to see objects closer than 1m from the eye. Calculate the focal length of the converging lens which is required to reduce this to 25cm.


Homework Equations



Lensmaker's equation: 1/u + 1/v = 1/f

u= distance from object to lens
v= distance of image to lens
f = focal length


The Attempt at a Solution



I tried using the above equation by substituting in u=1m, v=0.25m. But that doesn't help. The solution should be 33cm.
 
Physics news on Phys.org
Here the image is virtual.
So the formula should be
1/u - 1/v = 1/f.
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
View full post »

Thread 'Struggle to understand the concept of the question (ice cube in water optics question)'

TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
View full post »

Similar threads

Focal length of the eyepiece lens in a compound microscope
Replies
7
Views
1K
Calculate a radius of a circle on a screen
Replies
3
Views
1K
What is a focal length of a thin convex lens?
Replies
9
Views
2K
What Focal Length Eyepiece Provides a -125 Magnification?
Replies
1
Views
2K
Find the location and length of the final image
Replies
2
Views
887
Calculate the focal length of the spectacle lens
Replies
3
Views
3K
Image with an Plano-Convex lens
Replies
7
Views
3K
The focal length of a microscope eyepiece
Replies
1
Views
3K
Wave Physics - Optics - Effective Focal Length
Replies
12
Views
4K
How Do Sign Conventions Affect Focal Length Calculations?
Replies
8
Views
2K

Hot Threads

Recent Insights

Back
Top