Question

*PLEASE HELP*

Answer 1

Answer: The focal length of the lens = 3.32 cm.

Explanation:

Lens formula : $\dfrac1f=\dfrac1v-\dfrac1u$    (i)

f= focal length , v=image distance , u =object distance.

magnification: m = $\dfrac{v}{u}$   (ii )

Given: v= -12.8 cm , m =2.85

Put values in (ii), we get

$2.85=\dfrac{-12.8}{u}\\\\\Rightarrow\ u=\dfrac{-12.8}{2.85}\\\\\Rightarrow\ u=-4.49\ cm$

substitute values of u , v in (i)

$\dfrac1f=\dfrac1{-12.8}-\dfrac{1}{4.49}\\\\\Rightarrow\dfrac1f=-0.30084214922\\\\\Rightarrow\ f=\dfrac{-1}{-0.30084214922}\approx3.32\ cm$

Hence, the focal length of the lens = 3.32 cm.

Answer 2

Answer:

6.92

Explanation:

2.85=-(-12.8/x)

do=4.49

1/f= 1/4.49 + 1/-12.8

f=6.92