Question

(a) An object that is 3.27 cm high is placed 23.9 cm in front of a thin lens that has a power equal to 10 D. Draw a ray diagram to find the position and the size of the image and check your results using the thin-lens equation.

s'	= ______cm
y'	= ______cm

(b) Repeat Part (a) if the object is placed 18.4 cm in front of the lens

s'	= ______ cm
y'	= ______cm

(c) Repeat Part (a) for an object placed 20.8 cm in front of a thin lens that has a power equal to -10 D.

s'	= _____cm
y'	= ______cm

Answer 1

(a) We know the f = 1/P = 1/10 = 0.1 m or 10 cm

Now, use lens equation

1/f = 1/do + 1/di

where do is object distance and di is image distance.

1/di = 1/10 - 1/23.9

di = 17.194 cm

now, m = -di/do = -17.194 / 23.9 = - 0. 719 (inverted image)

also

m = hi/ho

-0.719 = hi / 3.27

hi = 2.35 cm (image is smaller)

(b) for do = 18.4 cm

1/di = 1/10 - 1/18.4

di = 21.9 cm

m = - 1.19 (as magnitude of m is greater than 1 , image is larger than object)

hi = 1.19*3.27 = 3.89 (image is larger than object)

(c) If p = -10 D

f = -10 cm

so,

di = - 6 .75 cm

virtual and same side of object

m = 0.3246

hi = 1.0616 cm