Question

A converging lens (f = 10.4 cm) is held 8.15 cm in front of a newspaper, the print size of which has a height of 1.98 mm.

(a) Find the image distance (in cm), d = cm

(b) The height (in mm) of the magnified print. h = mm

Answer 1

well you know the formula is (1/d) + (1/d') = (1/f)
d is the object distance which is 8.15 cm
d' is the object image distance from the lens

to find d' you just plug and chug
(1/8.15) + (1/d') = (1/10.4)

d'= -37.67

that means that the object is a virtual image
the magnification is found by -d'/d so that is
-(-37.67/8.15) your magnification is 4.62 which is a proportionality constant and you just multiply that with the height

so the final height is 4.62(1.98)=9.15mm