Image Magnification: Find Height of Image with f=42

[Noreturn]

Homework Statement

f=42[/B]
Find the height of the image produced when a 3.0 cm -high object is placed at distance f+10cm

Homework Equations

The Attempt at a Solution

1/52= 1/3 +1/di

di=49

However, this is wrong for some reason. Thanks

 

[Charles Link]

$f=42$ and doesn't change. $d_o=f+10=52$. Find $d_i$. After you do that, there's one more formula that you need. $\\$ Incidentally, your arithmetic is incorrect: $1/52 \neq 1/3+1/49$. When you solve for $d_i$ on this second try, you need to compute it with proper arithmetic.

 

[Noreturn]

$f=42$ and doesn't change. $d_o=f+10=52$. Find $d_i$. After you do that, there's one more formula that you need. $\\$ Incidentally, your arithmetic is incorrect: $1/52 \neq 1/3+1/49$. When you solve for $d_i$ on this second try, you need to compute it with proper arithmetic.

So di= 218.4

hi/ho=-di/do

hi/3=218.4/52

hi=-12.6cm

That is still wrong tho. I know it can't be negative just tells us it's inverted. Where did I go wrong?

 

[Charles Link]

So di= 218.4

hi/ho=-di/do

hi/3=218.4/52

hi=-12.6cm

That is still wrong tho. I know it can't be negative just tells us it's inverted. Where did I go wrong?

I agree with your answer. If it is a computer program, try inputting +12.6 cm. Usually these images are specified with positive heights even though they are inverted.

 

[Noreturn]

So I guess it wanted it input as a negative, (even though height can't be negative?). So when I do -12.6 it says very close try/check rounding. However when I do ((1/42)-(1/52))^-1 I get 4.2 so multiply that by 3 it's 12.6 even.

 

[Charles Link]

So I guess it wanted it input as a negative, (even though height can't be negative?). So when I do -12.6 it says very close try/check rounding. However when I do ((1/42)-(1/52))^-1 I get 4.2 so multiply that by 3 it's 12.6 even.

It's very fussy if it expects an answer of $h=-13$ cm because of two sig figs when the exact answer is 12.6. If I were giving it as a problem, I would call the answer $h=+12.6$ cm. One problem with computerized answers is that they are incapable of doing any thinking.