Question

Keesha is looking at a beetle with a magnifying glass. She wants to see an upright, enlarged image at a distance of 25 cm. The focal length of the magnifying glass is +5.0 cm. Assume that Keesha's eye is close to the magnifying glass.

(a) What should be the distance between the magnifying glass and the beetle?
(b) What is the angular magnification?

Answer 1

a) p = 4.167 cm, b) m = + 6

Step-by-step explanation:

a) For this exercise we must use the equation of the constructor

`(1)/(f) = (1)/(p) + (1)/(q)`

where f is the focal length, p and q are the distance to the object and the image, respectively

In this case the distance to the image q = 25 cm and the focal length is f = 5.0 cm

Since the object and its image are on the same side of the lens, the distance to the image by the sign convention must be negative.

`(1)/(p ) = (1)/(f) - (1)/(q)`

`(1)/(p) = (1)/(5) - (1)/(-25)`

`(1)/( p)` = 024

p = 4.167 cm

b) angular magnification

m = h ’/ h = - q / p

m = - (-25) /4.167

m = + 6

the positive sign indicates that the image is straight and enlarged