Question

5. How far would an object need to be placed from a mirror of focal length 10.0 cm if it is
image which is 20.0 cm BEHIND the mirror?
Insert your solution here:
I
Draw a ray diagram for this problem. (SCALE TO USE: 5 CM IS EQUIVALENT TO 1 INCH.
USE A LONG BOND PAPER FOR YOUR RAY DIAGRAM)​

Answer 1

Answer:

behind the mirror=means it is a convex mirror

so virtual errect image will formed

u=(-) object distance from mirror=?

v (+)=image distance from the mirror=20cm

f(+)=focal length=10cm

mirror formula

$\frac{1}{f} = \frac{1}{v } + \frac{1}{u}$

1/10=1/20 + 1/(-u)

1/(-u)= 1/10 -1/20

-1/u=(2-1)/20

-1/u=1/20

by cross multiplication

U= -20

so object is at centre

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Answer 2

Answer:

6.333 cm

Explanation:

Using Real Is Positive convention.

Part 1: v=+20 f=+10 u=???

1/u + 1/v = 1/f

I/u = 1/f - 1/v = 1/10 - 1/20 = 1/20

u = 20 cm

Part 2: v=-20, f=+10 u=???

1/u = 1/f - 1/v = 1/10 + 1/20 = 3/20

u = 20/3 or 6.333 cm