Question

In a cinema, a picture 2.5 cm wide on the film is projected to an image 3.0 m wide on a
screen which is 18 m away. The focal length of the lens is about:

Answer 1

The magnification is m = hi/ho and hi/ho = di/do. This can be solved for the distance to the image, and then the lens equation 1/do+1/di=1/f. Thus the focal length is 15 cm

http://hep.physics.lsa.umich.edu/p240/exams/exam3.html

Answer 2

thanks

Answer 3

Make sense?

Answer 4

hmmm actually no

isnt the equation
1/f=(1/i)+(1/p)

Answer 5

Go Here and look at problem number 4 it will help you: http://web.ics.purdue.edu/~jensend/media/pdf/phys241/exams/exam03/Fall2006.pdf

Answer 6

ok thanks

Answer 7

my image = 19.6...is that right?
and object = 1.6

but then it =1.47...?

Answer 8

if i convert to cm then its 147cm...somthing is wrong...