An object is held 2.1 cm away from a lens. The lens has a focal length of 0.4 cm

Question

An object is held 2.1 cm away from a lens. The lens has a focal length of 0.4 cm.

a.) Determine the image distance.
_____________ cm

b.) Determine the magnification.
____________

c.) If the object is 7.5 cm long, determine the image height.
_____________ cm

d.) Which of the following are true about the image? Choose all that apply.

1. The image is upright.
2. The image is virtual.
3. The image is inverted.
4. The image is real.


e.) Which of the following are true about the lens? Choose all that apply.

1. The lens is convex.
2. The lens is converging.
3. The lens is diverging.
4. The lens is concave.

Explanation / Answer

let the focal length of lens f = 0.4cm,  object distance from lens = 2.1cm

a) image distance v = ?  but lens formula (1/f) = (1/u) + (1/v)

(1/v) = (1/f) - (1/u)

v = (uf)/(u-f) = (2.1*0.4)/(2.1-0.4) = 3.57cm

b) magnification m = v/u = 3.57/2.1 = 1.7

c) if the object size OJ = 7.5cm,  image size IO = ?

but m = IO/OJ  

 image size IO = m*OJ = 1.7*7.5 = 12.75cm

d) the image is up right ,  and the image is virtual.

e) the lens is diverging lens, and the lens is concave.

 

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