### Tut 2 Coulomb

**1. **Two objects A and B carry charges of -8nC and 2nC.

They are placed a distance of 0,02m apart.

**1.1.** Calculate the magnitude of the electrostatic force between them.

**1.2.** Name the law used to calculate the above force.

**1.3. **Why do both charges experience the same magnitude of force?

**1.4.** What would happen to the magnitude of the force if the distance between the charges were increased?

**1.5.** What is the nature of the force?

1.2. Coulombs Law

1.3. Newton's Third Law

1.4. Force would decrease (inverse proportion)

1.5. attractive (unlike charges attract)

**2.** The magnitude of the electrostatic force between charges X and Y placed 24mm apart,

is exactly 3 x 10^{-5}N.

The charge on X is 6uC.

**2.1.** What is meant by 6uC?

**2.2.** Calculate the magnitude of the charge on Y.

2.1.

6 x 10

^{-6}C

2.2.

**3.** Charge A (+8 x 10^{-6}C) is attached to the ceiling by a thin string.

Charge B (-4uC) is balanced in the air 12mm below charge A.

**3.1.** Calculate the electrostatic force between objects A and B.

**3.2.** What is the mass of B?

**4.** Calculate how far apart two charges of magnitude 5nC each must be placed, so that the electrostatic force between them becomes 4 x 10^{-7}N?

4.

**5.** Object A is held by a thin silk thread as shown at an angle of 15^{0}. The mass of A is 2g.
The distance between A and B is 22cm, and the charge of B is +8uC.

**5.1.** Draw and label all the forces acting on A.

**5.2.** Calculate the weight of A.

**5.3.** Calculate the charge of A.

5.1.

Fe = electrostatic force

T = tension

w = weight

5.2.

5.3.

**6.** The force between charges Q_{1} and Q_{2} is F. If the distance between the charges is doubled, what would be the new magnitude of the force?

6. ^{F}/_{4}

**7.** The charge of A is Q and that of B is 3Q. The interacting force has a magnitude of F. If the charge of A is doubled, and that of B is halved, what would be the new force if the distance between them is halved?

7.

4F

**8.** The force between two charges X and Y of magnitude 3Q and 5Q respectively a distance of r apart, is F. How far apart must the charges be placed, so that that the force becomes 2F if the charge of X is doubled?

8. still r

no change to distance

**9.** Three charges are arranged in a straight line as shown.

Calculate the resultant force on Y.

9.

**10.** A 10g pith ball A, carrying a charge of +200nC is placed at the bottom of a tall, narrow glass tube which is on an insulated stand.
A second pith ball B of the same mass and carrying the same charge as A is introduced at the top of the cylinder.

If no charge is lost to the surroundings, calculate the height h at which B will be suspended above A.

10.

**11.** Three charges are arranges in a right angle pattern as shown.

Calculate the resultant force on B.

10.