A copper ball of mass 81 g is positively charged to +423 C. It is attached to a

Question

A copper ball of mass 81 g is positively charged to +423 C. It is attached to a metal plate by a plastic, insulating spring of equilibrium length 29 cm and strength 5.45 N/m.

(1) If the plate is not charged, what is the extended length of the spring? ______cm

(2) Using standard data for copper, estimate the number of atoms there are in the ball per excess electron that charges it. ______atoms/e-

(3) If the plate is attached to a power supply and the ball raises back to its equilibrium length, what is the magnitude of the electric field it puts out? ______N/C

Explanation / Answer

(1) Fnet = kx - m g = 0

5.45 x = (81 x 10^-3) (9.8)

x = 0.146 m or 14.6 cm

extended length = L0 + x = 43.6 cm

(2) Q = n e

n = (423 x 10^-6) / (1.602 x 10^-19)

n = 2.64 x 10^15 electrons

atoms = mole NA = (81 / 63.5) (6.022 x 10^23)

= 7.68 x 10^23 atoms

ratio = (2.64 x 10^15) / (7.68 x 10^23)

= 3.44 x 10^-9

(3) Fnet = q E - m g = 0

(423 x 10^-6) E = (81 x 10^-3) (9.8)

E = 1877 N/C

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.