Question

An object is placed at 30.0 cm in front of a converging lens. The lens has a focal length of 10.0 cm. What are the values of the image distance and magnification respectively?​

• A. 60.0 cm and 2.0
• B. 15.0 cm and 2.0
• C. 60.0 cm and -0.5
• D. 15.0 cm and -0.5

Answer 1

The correct option is D 15.0 cm and -0.5

Using the lens equation,​

1/v - 1/u = 1/f​

where, u = 30.0 cm and f = 10.0 cm.​

Solve for v :​

1/v = 1/f + 1/u ​
1/v = 1/(10.0 cm) - 1/(30.0 cm) ​
1/v = 0.0666 $c{m}^{-1}$
v = 1 / (0.0666 $c{m}^{-1}$) = 15.0 cm​

​Then, using the magnification formula,​

m = -v/u to find m​
(u = 30.0 cm; v = 15.0 cm)​

​Substitute and solve for m:​

m = -(15.0 cm) / (30.0 cm) ​
= - 0.5