00:01
So we have an object placed in front of a converging lens at a certain distance, and we're told the focal length of this lens is, i think, 0 .33 meters.
00:14
And so we want to know if the magnification of this setup is originally 5 .3, and we want to move the object so that the magnification becomes negative 5 .3, what direction do we have to move it? well, if you have a converging lens and a positive magnification, that basically means you have a negative image distance, which means you're within the focal length, or you're between the focal length of the lens and the lens.
00:41
So we need to move the object backwards in order to achieve a negative magnification, because the magnification is the negative image distance.
00:51
I'll call that s prime over the object distance.
00:54
We'll call that s.
00:55
And so whenever the magnification is positive, it means s prime is negative.
00:59
And s prime is negative whenever the object is in front of the focal length of the lens and so anyway to figure out where should the object be moved or what distance should it be moved we need to know what distance is it originally at and then what distance does it need to be at finally so the image distance s prime if we kind of solve generally for our converging lens is going to be like the focal length times the object distance over the object distance minus the focal length.
01:39
And so the magnification is going to be negative s prime over s.
01:43
And so if we plug that in, what we're going to get is f over f minus s...