Question

Using a thin lens with a focal length of f = +5.2cm, a student makes two measurements. She finds the distance to the object to be o = +3.1cm. What distance, i, should she expect for the image? Explain whether this is a real or virtual image using the sign convention. Then find the magnification of the image also explaining your answer using the sign convention.

Answer 1

1.

f = focal length = 5.2 cm

o = object distance = 3.1 cm

i = image distance = ?

using the lens equation

1/f = 1/o + 1/i

1/5.2 = 1/3.1 + 1/i

i = - 7.7 cm

since the image distance is negative , as per sign convention , the image is virtual.

magnification is given as

m = - i/o

m = - (- 7.7)/3.1 = 2.5

since the magnification is positive , the image is upright.