2 Physics questions !!?

Question

1. What r some similarities and differences between the electric force and gravitational force ?

2. A small glass rubbed silk gains a charge of + 2.0 C. THe glass ball is placed 12 cm from charged rubber ball that carries a charge of -3.5 C
a. What is the magnitude of the electric force between the 2 balls?
b. Is this force attractive or repulsive?
c. How many electrons has the glass ball lost in the rubbing process?

Answer 1

1) They are similar because the strengths of the forces are inversely proportional to the distance between the objects. They are different because the gravitational force is always attractive while the electric force can be attractive or repellent.

2) a) It's F = k(q_1)(q_2) / r^2, where k is the electrical constant (8.99 x 10^9 N-m^2 / C^2) that should be in your textbook, q_1 and q_2 are given as 2 C and -3.5 C, and r is the distance between them, 12 cm = 0.12 m.

b) The force is attractive because the charges are unlike each other (one positive, one negative).

c) You need to divide the charge on the glass ball, 2 C, by the charge on a single electron, 1.6 x 10^-19 C.

Answer 2

1. Similarity: Both forces obey a 1/r^2 law - they get weaker as the objects separate.

Difference: The electric force involves two polarities (positive and negative) of electrical charge and cna be either repulsive or attractive. There is only one polarity in gravity, hence it is always attractive.

Difference: gravity is orders of magnitude weaker than electrical force.

2. Start with F = k*q1*q2/r^2 where k=1/(4*pi*e0) = 8.99*10^9 Nts-m^2/(coul^2)

a. mag(F) = abs(k*2 coul*(-3.5)coul)/(0.12m)^2) = 9.06*10^8 Nts

b. Force is attractive since charges are of different signs.

c. charge on 1 electron = -1.6*10^-19 coul so number of electrons in 2 Couls = 2/1.6*10^-19 = 1.25*10^19