## Monday, January 18, 2010

### Irodov Problem 3.5

Consider an infinitesimally small section of the ring that subtends an angle at the center. The charge contained in this infinitesimally small section of the ring is . The force exerted by the charge q0 on this infinitesimally small section of the ring is given by,

Let T be the tension in the ring induced due to the electrostatic force resulting from charge q0. The rest of ring exerts this force T on each of the two ends of the infinitesimally small segment of the ring. The component of this force T in the direction of dFe (as shown in the diagram) is given by . Since the infinitesimally thing ring section is in equilibrium (no accelerating) using Newton's second law we have,

1. the final answer is having dθ, but it was canceled in the step just above it!

1. It's been a mistake

2. it is just a writing error. final answer won't contain d@. rest of the answer is perfectly correct

3. Change in Tension is required but it is only the final Tension

1. look shubham try to reakise that the tension in the ring initially is zero due to no F external so change in the force will be this only.i hope you will try to understand......................................................................................................................................................................................

2. It is not 0. We have to find change in tension. The intial tension in the ring is already balancing the forces by the ring electrostatic repulsion.As we can see by symmetry that its direction will be radially outward (same as that of the new repulsion)so the increase will happen only due the central charge force. Hence we are assuming initially 0 which is just a reference point.

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5. How did the charge in the small section of the ring = qd@/2π

6. Why have we not considered the electrostatic force due to remaining part of ring?...please reply

7. Why have we not considered the electrostatic force due to remaining part of ring?...please reply

1. We have to find change in tension. The intial tension in the ring is already balancing the forces by the ring electrostatic repulsion.As we can see by symmetry that its direction will be radially outward (same as that of the new repulsion)so the increase will happen only due the central charge force.