1Thanks, forgot to mention it was uniform..
Any takers for #2?
1. A loose thread is given a +Q charge. It immediately takes a circular shape. Why?
2. What is the increment in tension caused by placing a charge Qo at the centre of a uniformly charged ring of radius R? The ring has a uniformly distributed +Q charge.
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6 Answers
621) depends on if the thread is uniformly charged. (Which will not always be the case)
If the thread is not charged uniformly, it will not take a circular shape..
Otherwise there will be "symmetric" repulsions that will cause it to become circular.
162The second part is the more interesting one..
you have to take an element of angle d theta from the center.
The charge on that element will be Q/(2pi R) . (R dθ) = Q (dθ/2pi)
Now draw the fbd of the element.
The force on the element will be
Initilaly if force F0 acts on the elemtn, then
F0=2(T) sin(dθ/2)
Later force acting increases due to the charge at the center
k Q (dθ/2pi)Q0r2+F0=2(T+ΔT) sin(dθ/2)
SInce dθ is very small, you can replace sin by the angle itself.
so
k Q (dθ/2pi)Q0r2=2ΔT sin(dθ/2)
k Q Q02pi r2=ΔT
1thankss..one doubt: how did u get Fo--the initial force?
62THe trick here is that i never found F0
If you see closely, it got cancelled out with the 2nd equation..
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