A converging lens produces an image four times as large as an object placed 25cm from the lens. Calculate its focal length

smartychuks

10 years ago

haha...i see some incomplete calculations here man

okay it's like this using the formula above (M=V/U)to find the image distance(V) since the object distance (U) is already given as 25 and magnification is 4

substitute the gotten value in the lens equation 1/f=1/U+1/v

solve

1/F=1/100+1/25

multiply both sides by lcm 100

100(1/F)=(1/100+1/25)100

100/F=1+4

making f the subject for the formula

therefore;

F=100/5

as such the focal length (f) is 20cm



all the best

smarty

Bukason.

10 years ago

The selected answer is wrong:

Focal lenth(F)= (VxU)/(V+U)...m(4)=v/u...v=4u...F=(4ux25)/(4u+25) .: u=25,,f=(100x25)/(100+25)...f=2500/125...f=20cm{D)

REF: New School Physics/Application of light waves

Award0001

2 years ago

it would have been nicer if they soecied if the image formed was virtual or real but since they didn't specify it was taken as real
m= 4
u= 25cm
m = v/u
v = m*u = 4*25 = 100cm
1/f = 1/u + 1/v
1/f = 1/12 + 1/100
1/f = 0.04 + 0.01
1/f = 0.04 + 0.01
1/f = 0.05
0.05f = 1
f = 1/0.05 = 20cm

Myschool Blessing

10 years ago

Thanks for your contributions. corrections have been made.

Dmony

1 year ago

Why did I get 8