Optics : When to use the negative / positive signs?

This forum made possible through the generous support of SDN members, donors, and sponsors. Thank you.

orangeblue

Full Member
10+ Year Member
Joined
Feb 10, 2011
Messages
895
Reaction score
126
I'm wondering when to use negative/positive signs?

I know that virtual side is always *negative** correct?
real side is always *positive* correct

In lenses, the virtual side is the side that the object is place
In mirrors, the virtual side (since the mirror only has one side where the light reflects from) is the "dull" side ie. side opposite of the convex/concave mirror curve.

In the 1/f = 1/o + 1/i , where does the negative sign go if at all?
Or is it only for m = height image / height object = - distance image / distance object?

Members don't see this ad.
 
if you do your math correctly, you don't need to worry about signs because the lens equation will figure all that.

but for reference, know this. diverging lenses and mirrors always make smaller, upright, and virtual images


and converging lenses and mirrors make inverted and real images, except when your object is within the focal plane; then it makes a upright virtual image thats larger
 
...but for reference, know this. diverging lenses and mirrors always make smaller, upright, and virtual images


and converging lenses and mirrors make inverted and real images, except when your object is within the focal plane; then it makes a upright virtual image thats larger

Perfectly explained! I was set to respond, but you hit on the key points already. Well done Phattestlewt. I'm assuming from the SUV for diverging systems and IR/LUV for converging systems approach, you used BR books.
 
Perfectly explained! I was set to respond, but you hit on the key points already. Well done Phattestlewt. I'm assuming from the SUV for diverging systems and IR/LUV for converging systems approach, you used BR books.
Yes indeed! :)

Thanks for the help TBR!

(great prep materials btw +1, bio 2 was a little dense to get through though)
 
Top