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I cannot figure out if the image is a positive or negative number. Because you c

ID: 1445939 • Letter: I

Question

I cannot figure out if the image is a positive or negative number. Because you can end up with two different answers depending on if M= - ( - DI /DO) or whether M= - (DI/DO)

1)Then solve I solved for DI.

2) Then I plugged it into: 1/F= 1/DO+1/DI But depending on whether the image is positive or negative the numbers are different.

Without drawing a diagram. How do I know if the image will be positive or negative. -Thanks

An object is located to the left of a convex lens whose focal length is 36cm. the magnification produced by the lens is m=3.0. a. To increase the mag to 4.0, should the object be moved closer or farther? Explain b. calculate the distance through which the object should be moved....

Explanation / Answer

for convex lens, focal length is positive.

f = +36 cm

m = - (di / do) = 3

di = - 3do

Using lens equation,

1/f = 1/di + 1/do

1/36 = 1/(-3d0) + 1/do

1/36 = 0.6667 /do

do = 24 cm

and when m = 4 = - di/do

di = - 4 do

1/36 = 1/(-4do) + 1/do

1/36 = 0.75/do

do = 27 cm


so we have to move object farther.

deltad = 27 - 24 = 3 cm

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