PHYsICS!!!!!!!!!!?

[Sasha45]

Physics homework help!!!!! very important, need to get an A?
an object is placed in front of a diverging lens with a focal length of 20.0 cm. For each object distance, find the image distance and the magnification. Describe each image.

a. 40 cm
B. 20.0 cm
C. 10.0 cm

i think one equatiom might jog ur memory, like 1 over p plus 1 over f equals 1 over q or something like tht, plz help me, i need to pass physics fo this quarter, i did the 1st 6 problems, but cant get these last two. thnx very very much

[VanessaJGibbs]

Ok, it's been a real long time so I had to pull out the formulas and this is what I came up with.

a. f = 20
O = 40
I = 40
M = -1

b. f = 20
O = 20
I = 0
M = 0

c. f = 20
O = 10
I = 20
M = -2

a. 1 / I + 1 / 40 = 1 / 20
1 / I = 1 / 20 - 1 / 40
1 / I = 1 / 40
I = 1 / .025
I = 40

M = - I / O
M = - 40 / 40
M = -1

b. 1 / I + 1 / 20 = 1 / 20
1 / I = 1 / 20 - 1 / 20
1 / I = 0

M = - I / O
M = - 0 / 20
M = 0

c. 1 / I + 1 / 10 = 1 / 20
1 / I = 1 / 20 - 1 / 10
1 / I = - 1 / 20
I = 1 / .05
I = 20

M = - I / O
M = - 20 / 10
M = - 2

I could have missed the boat entirely, but, here's the math. Work it yourself and check.

Hope it helps!!