A 6 cm high object is placed 43ncm from a converging lens of focal length 24 cm. Find the image’s position and draw a ray diagram approximately to scale.

Answer 1

B) To answer this question you use 1/f = 1/v + 1/u where f is the focal length, v is the image distance, and u is the object distance

v = 1/(1/24 - 1/43) = 54.3cm

Note that since the object distance exceeds the focal length, the image will be real and inverted.

To construct the ray diagram draw a horizontal line OLB representing the optical axis. At L (about 1/3 the way from O, erect a perpendicular CLD representing the lens. Erect another shorter perpendicular OO' at O representing the object. Mark the focal point (F) of the lens at a suitable point on LB scaled relative to the object distance OL.

From O' draw a line parallel to AB striking CLD at X. From X draw a line XF and project it beyond F. From O' draw another line O'L and project it beyond L until it intersects XF (projected) at I'. I' is the point on the image which corresponds to O' on the image. Drop a perpendicular from I' to AB and mark the point I where this line intersects AB. I is the point on the image which corresponds to O on the object