An object is held 46.9 cm away from a lens. The lens has a focal length of -22.8
ID: 1703247 • Letter: A
Question
An object is held 46.9 cm away from a lens. The lens has a focal length of -22.8 cm.a.) Determine the image distance.
__cm
b.) Determine the magnification.
_____
c.) If the object is 0.9 cm long, determine the image height.
__cm
d.) Which of the following are true about the image? Choose all that apply.
__The image is real.
__The image is virtual.
__The image is upright.
__The image is inverted.
e.) Which of the following are true about the lens? Choose all that apply.
__The lens is converging.
__The lens is diverging.
__The lens is concave.
__The lens is convex.
Explanation / Answer
Object distance, do = 46.9 cm
Focal length, f = 22.8 cm
(a)
From the lens equation,
1 / f = (1/ do) + (1 / di)
(1/di) = (1/f) -(1/do)
= (1/ 22.8 ) - ( 1/ 46.9 )
= 0.044 - 0.0213
= 0.0227
Image distance, di = 44.1 cm
(b)
Magnification, M = - di / do
= - 44.1 / 46.9
= - 0.94
(c)
Magnification, M = h' / h
Image height, h' = M * h
= - 0.94 * 0.9
= - 0.85 cm
[ Here, -ve sign indicates inverted image ]
(d)
Image is real because image distance is positive
Image is inverted because the image height is negative
(e)
The lens is convex (or ) converging since the focal length is positive.
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