Recent content by notgoodatphysics

Great, appreciate the advice, thanks! I’ll arrange a time with her and see what she says. Perfect, cheers!

No that’s the issue, UP are far too easy in comparison to the questions we are given by our professor. I‘ll have a look at both of them, cheers.

Currently in 1st year (UK) going through E&M right now, the recommended textbook is University Physics by S&Z. Recently had my-mid term test and got 40%. The problem is I’m overestimating my ability as the exercises in UP are not challenging at all, the majority of them are just plugging in...

I understand that bit. But it’s presented in the book as an example, and he mentions specifically that you have no idea it’s circle, so suppose you were presented with the original equation and asked to find the minimum/ maximum. You’d need find the derivative if I’m not mistaken? My confusion...

Right, but you’d know this without having to find the derivative. I guess if you didn’t know it was a circle there’s an explanation to “Since no value whatever of x will make the denominator infinite, the only condition to give zero is x = a”?

We have the equation for a circle, and its derivative: $$(y-a)^2 + (x-a)^2 = r^2$$ $$\frac{dy}{dx} = \frac{a-x}{(r^{2}-(x-a)^2)^{1/2}} = 0$$ So ##x = a## then he subs it into the original equation to get the max/min. Why does ##x = a## give the points of minima/ maxima if we didn’t know it...

Thanks for the reply! I’m not sure I’m totally understanding the need for z’ though. In the example of the electric field of due to a ring of charge with radius a, to find the electric charge due to a disk, the integral from 0 to R is calculated - isn’t this a similar case? Why isn’t it (a-R)...