An image in a convex lens is upright and magnified 3 times. If the focal length of the lens is 15 cm, what is the object distance?

ddumebiii

2 years ago

for anyone confused like i was:
convex lens, f is +ve
concave lens, f is -ve
real image, v is +ve
virtual image, v is -ve (which means m would become -ve)

Award0001

2 years ago

remember its a converging lens sonit will have a real focus but the image is virtual (case 5)
therefore 1/f = l/u - 1/v
multiple through by v you get v/f = m - 1

v/15 = 3 -1
v/15 = 2
v = 15×2 = 30cm

m = v/u
3 = 30/u
u = 30/3 = 10cm

Nwese

5 years ago

according to the question, u will have to make use of a simple microscope formula
M= D/U,
3=D/U
D=3U
M= (D/ f)+1.
3-1=(3u/15)
2=3u/15
u=30/3
u=10//

gbenga229

1 year ago

No option

Joshie777

12 years ago

hiu=hov; where hi=-3ho. So, subst. for hi, -3hou=hov u=(hov)/(-3ho) u=-v/3. Now recall that 1/f=1/u+1/v. So, subst. for u, 1/f=-3/v+1/v 1/15=-2/v; cross multiplying,v=-30...but u=-v/3 So,u=-(-30)/3 u=10cm