A thin lens has a focal length of 250 cm a Locate the image

A thin lens has a focal length of 25.0 cm.

(a) Locate the image when the object is placed 28.0 cm in front of the lens. (Enter a negative distance if the image is in front of the lens.)
cm from the lens Choose the correct description of the image. (Select all that apply.)

inverted

enlarged

reduced

upright

virtual

real

(b) Locate the image when an object is placed 23.2 cm in front of the lens. (Enter a negative distance if the image is in front of the lens.
cm from the lens Choose the correct description of the image. (Select all that apply.)

inverted

reduced

virtual

real

enlarged

upright

Solution

a)

f = 25 cm

d_o = object distance = 28 cm

d_i = image distance

using the lens equation

1/d_i + 1/d_o = 1/f

1/d_i + 1/28 = 1/25

d_i = 233.33 cm

m = - d_i/d_o = - 233.33 / 28 = - 8.33

since m is negative , the image is inverted

since m > 1 , the image is enlarged

the image is real

the image is formed on the other side of the object

b)

f = 25 cm

d_o = object distance = 23.2 cm

d_i = image distance

using the lens equation

1/d_i + 1/d_o = 1/f

1/d_i + 1/23.2 = 1/25

d_i = - 322.22 cm

m = - d_i/d_o = - (- 322.22) / 23.2 = 13.88

since m is positive , the image is upright

since m > 1 , the image is enlarged

the image is virtual

the image is formed on the same side of the object