The “Fun Fly Stick,” is a tube with a static electricity generator inside. When

ID: 1875217 • Letter: T

Question

The “Fun Fly Stick,” is a tube with a static electricity

generator inside. When you run the device, a belt moves positive charge up the tube,

depositing it at the end. If you run the motor for about 2 seconds, a charge of +350 nC

accumulates at the tip of the tube. A lightweight piece of foil will be attracted to the tip of the stick, touch it, then fly away. At

this point, you can move the tube to levitate the foil, holding it motionless in the air.

1) What is the approximate magnitude of the current inside the tube when the motor is turned on?

A. 0.2 µA

B. 2 µA

C. 20 µA

D. 200 µA

2) Why is the foil initially attracted to the tube?

A. Charges from the tube fly through the air and are deposited on the foil.

B. The positive charge on the tube creates a net negative charge on the foil by induction.

C. The foil is neutral, but charges separate and the attractive force of the close charges dominates.

D. The piece of foil is curious, and is simply trying to get a good look at the tube.

The thin piece of foil has a very small mass—only 75 mg. If it levitates 20 cm above the tube, what is the sign and the magnitude

of the charge on the foil?

1) current = charges flowed in time / time interval

= (350 x 10^-9) / 2

= 0.175 x 10^-6 A

Or 0.2 uA

Ans(A)

2) (C)

3) Fe = Fg

k q1 q2 / r^2 = m g

(9 x 10^-9)(q1)(q2) / (0.20^2) = (75 x 10^-6)(9.8)

q1 q2 = 3.27 x 10^-15 C

and q1 + q2 = 350 x 10^-9 C

q1^2 - (350 x 10^-9) q1 + 3.27 x 10^-15 = 0

q1 = 340 x 10^-7 C

and q2 = 9.6 x 10^-9 C

charge on it = 9.6 x 10^-9 C Or 9.6 nC

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