IMathAS-libretexts

The figure shows a large insulating sphere with charge $\displaystyle {Q}$ near an uncharged conducting rod. The figure also shows a small conducting ball with charge $\displaystyle {q}$ â‰ª $\displaystyle {Q}$ suspended from a string, which has a negligible effect on the charges on the other objects and can be used as a test charge. Students perform an experiment intended to determine how the sphere affects the charge separation within the rod. They observe the angle of the string when the ball is at the two positions to the right of the rod shown. Which of the following is a problem with the procedure that affects how well it can accomplish the experimental goal?

The force on the ball is affected by its distance from the end of the rod.
The effect of the electric field of the sphere at different points on the rod depends on the distance those points are from the sphere.
The ball is affected by the fields from both the sphere and the rod, so the effect of the charge separation on the rod cannot be isolated.
The separation of charge on the rod depends on the sign of the charge on the sphere.

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