Question
A lantern gives an image of 3m square of a side 7.62cm² on a screen. If the screen is 10m from the projection lens of the lantern, calculate the focal length of the lens?
Answers
oobleck
the side of the projection is √7.62 = 2.76 cm
Now you can use your usual formula to find f, since you have the object and image sizes.
Now you can use your usual formula to find f, since you have the object and image sizes.