A ping-pong ball has been electrostatically charged such thatit has 2.5 x 10 15

Question

A ping-pong ball has been electrostatically charged such thatit has 2.5 x 1015 excess electrons. The ball has a massof 1.0 g. It is observed to float motionless in the presence of auniform electric field. What is the magnitude and direction of thiselectric field. Hint: The ping-pong balls weight = mg is adownward force. g is the acceleration due to gravity = 9.8m/s2. A ping-pong ball has been electrostatically charged such thatit has 2.5 x 1015 excess electrons. The ball has a massof 1.0 g. It is observed to float motionless in the presence of auniform electric field. What is the magnitude and direction of thiselectric field. Hint: The ping-pong balls weight = mg is adownward force. g is the acceleration due to gravity = 9.8m/s2.

Explanation / Answer

Given that the number of excess electrons on ball are N= 2.5x1015 Then the charge of the ball is Q = N*e                                                  = 2.5x1015 *1.602*10-19 C                                                = 4.0x10-4 C The mass of the ball is m = 1.0 g = 1.0x10-3 kg Since the ball float motionless in the presence of a uniformelectric field, the electric field direction must be upward and itbalances the weight of the ball              so    F = mg                  EQ = mg                      E = mg / Q                          = ----------- N/C       where g = 9.8m/s2 is theacceleration due to gravity.

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