First I want to say thanks in advance - I found this site through Google and am thrilled! All I have left to graduate is Physics II (Electromagnetism & Waves), so I'll finally be walking on August 5. IF I can pass this class, that is.(adsbygoogle = window.adsbygoogle || []).push({});

I'm a non-traditional student, and it's been about 10 years since I had the first physics, or calculus. So I'm struggling...

I ran across this discussion (https://www.physicsforums.com/showthread.php?t=92557) thanks to Google, which lists my question almost to the T, but I'm still lost - I can't figure out where to go from here. I feel like our professor hasn't shown us nearly enough examples - he's spent most of the lecture time talking about theory, which makes sense to me until he throws math at me. Then I'm lost!

Remember I haven't had calculus in years and years, so bear with me....

THE PROBLEM:

A line of positive charge is formed into a semicircle radius R=0.6m.

The charge per unit length is given by [tex]\lambda=\lambda_{0}cos\theta[/tex].

The total charge on the semicircle is 50[tex]\mu C[/tex] Calculate the total force on a charge of 8[tex]\mu C[/tex] placed at the centre of the curvature.

The semicircle is like the top half of a circle with center as the origin. The angle [tex]\theta[/tex] is measured from the y axis.

(thank God for the quote button while I figure this latex stuff out!!)

Ok, I have no idea if this is right or not, but what I came up with is (I guess you can't specify limits of integration w/ latex?)

[tex]F= \frac {kq_{0}} {r^2} \int cos\theta d\theta [/tex]

uh.... I think? integrate that from 0 to [tex]\pi[/tex]? but the integral of cos is -sin, right? and sin 0= sin[tex]\pi[/tex]= 0. right?

and what the heck does the total charge of 50[tex]\mu C[/tex] have to do with anything?

I'm so lost....

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# Homework Help: Electric Force, linear charge density

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