## sha0403 Group Title suppose you have a convex lens with focal length 17 cm.if an object is place p cm away from the lens,its image will appear to be q cm from the lens, where p,q and 17 cm are related by the following equation:- 1/17=1/p + 1/q This is known as lens equation. what the rate of change of p with respect to q? one year ago one year ago

1. Shadowys Group Title

You might want to differentiate this. Did you attempt it?

2. sha0403 Group Title

3. Shadowys Group Title

Differentiate the $$\frac{1}{17}=\frac{1}{p}+\frac{1}{q}$$ wrt to q. Like this: $$\frac{d(\frac{1}{17})}{dq}=\frac{d(p^{-1})}{dq}+\frac{d(q^{-1})}{dq}$$ $$0=-p^{-2}p'-q^{-2}$$ So $$p'=- \frac{p^2}{q^2}$$ Now sub $$p=(\frac{1}{17}-\frac{1}{q})^{-1}$$ into that and you've got it.

4. sha0403 Group Title

what meaning of p' ?

5. Shadowys Group Title

$$p'=\frac{dp}{dq}$$

6. sha0403 Group Title

yes i got it..thanks a lot..:)

7. Shadowys Group Title

You're welcome :)