Question

21.65 -. If we rub a balloon on our hair, the balloon sticks to a wall ceiling. This is because the rubbing transfers electrons from our hair to the balloon, giving it a net negative charge. When the balloon is placed near the ceiling, the extra electrons in it repel nearby electrons in the ceil- ing, creating a separation of charge on the ceiling, with positive charge closer to the balloon. Model the interaction as two point-like charges of equal magnitude and opposite signs, separated by a distance of 500 um. Neglect the more distant negative charges on the ceiling. (a) A typical balloon has a mass of 4 g. Estimate the minimum magnitude of charge the balloon requires to stay attached to the ceiling. (b) Since a balloon sticks handily to the ceiling after being rubbed, assume that it has attained 10 times the estimated minimum charge. Estimate the number of elec- trons that were transferred to the balloon by the process of rubbing

Answer 1

= cinco e 500 км = 560X10-6 m 5x104m = m = Ag 4x10-3 • kg a) q,=92 ..? Electrostatic attraction q, az Fa uneo cinco qa =94109 g=9.81 m/s? F 3. weight of 45Eo balloon, - mg W= for the balloon to stay attached to ceiling, W = q? ² mg ra de bou 20 = 2 -3 4x10 Cano *9.814C 5*10-4) 9x109 = CS Scanned with CamScanner = 1.09x10-18 qa

.. Minimum chauge required, q 1.09 x 1018 = 1.044 X109c Since the change is ove, q -ac Caus -1.044 X10 Since the change = aquired is 10 times, q -1.044 X10-9X10 = -1.044 X10 8 C .: No. of electrons is given is given by q =be o/ 11 >> n X10-8 li -1.044 X -1.6 X10-19 = 6.52 x 100 electrons (Aus) CSScanned with CamScanner

2 O = 60° ; A = 6.66 X104 mi = 4.44 Nm²/C ' E = E = ? we bave, electric field 'E' 'E' givers by d = EA cos ! E A cos o 4:44 6.66x15 4x cos 60° 1.33x 104 Nic Cans) CS Scanned with CamScanner