Repulsive Force 3.3 Repulsion force. A very thin tube contains at its bottom a s

Question

Repulsive Force

3.3 Repulsion force. A very thin tube contains at its bottom a small plastic ball charged with a charge Q = 0.1 MuC as shown in Figure 3.33. A second, identical ball with identical charge is inserted from above. Assume there is no friction and the glass does not affect the charges on the balls. If each ball has a mass m = 1 g and the permittivity of the tube may be assumed to be the same as that of air (free space) calculate: (a) The distance between the balls if the tube is vertical (Figure 3.33a). (b) The distance between the balls if the tube is tilted so it makes an angle alpha = 30degree with the horizontal (Figure 3.33b). Problems 131

Explanation / Answer

to be in vertical   net gravitational force = couloubs force

so

Kq1q2/r^2 = mg

where k is permittivity cosntant = 9e9

q1 q2 are mag of charges each = 0.1 uC

r is the distance between them = ?

m is mass and g is accleration due to gravity

so

r^2 = Kq1q2/mg

r^2 = (9e9 * 0.1 e-6 * 0.1 e-6)/(1 e-3 * 9.8)

r = 9.58 cm

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when at vetrical mg cos theta = Kq1q2 sin theta/r^2

r = 9.58 * tan 30

r = 5.53 cm

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