PHYS 1100 Electrostatics

Physics 1100 In-Class Problems: Electrostatics

What is the net force on charge A in each configuration shown below? The distances are r₁ = 12.0 cm and r₂ = 20.0 cm.

The distances in the diagram below are are r₁ = 12.0 cm and r₂ = 20.0 cm.
(a) Find the net Coulomb force on charge A in component form.
(b) Find the net Coulomb force on charge B in component form.
(c) Find the net Coulomb force on charge C in component form.
Where would you put a positive charge of +1 μC in the diagrams below so that the net electrostatic force on it is zero?

The distances on the graph below are in metres. The charges are Q₁ = –3 μC, Q₂ = 2 μC, and Q₃ = 5 μC.
(a) Find the net force on charge Q₁ due to charges Q₂ and Q₃.
(b) Find the net force on charge Q₂ due to charges Q₁ and Q₃.
(c) Find the net force on charge Q₃ due to charges Q₁ and Q₂.
A charged ball of mass m = 0.265 kg and unknown charge q is hanging by a light thread from a ceiling. A fixed charge Q = +5.00 μC on an insulated stand is brought close to the unknown charge. As a result, the unknown charge now hangs motionless at an angle θ = 38.0° to the vertical as shown in the diagram below. The distance between the two charges is r = 22.0 cm.
(a) What is the sign of the unknown charge? Explain how you know this.
(b) What is the tension in the string?
(c) What is the magnitude of the unknown charge?

What is the net electric field at point A in each configuration shown below? The distances are r₁ = 12.0 cm and r₂ = 20.0 cm. In each case, determine the magnitude and direction of the electrostatic force on a charge put at point A if the charge is (i) -5 μC, (ii) 2 μC, or (iii) -7 μC.
Find the net electric field at point A in the diagram below.

A small ball of mass m = 0.015 kg is suspended floating with nothing touching it in an electric field of magnitude E = 5000 N/C. (a) If the electric field is pointing straight up into the air, what is the charge on the ball? (b) If E points straight down?
A ball of mass m = 0.010 kg and charge q is tied by a very light string to the ceiling. The effects of a uniform electric field E = 5000 N/C has caused the charged ball to move to one side so that the string makes an angle of θ = 37° with the vertical. It hangs there motionless. Draw the free body diagram of the floating ball. Determine the magnitude of the charge q. How can you tell the sign (positive or negative) of the charge?

A small charge of mass q = -5.0 nC and mass m = 0.100 g is released from rest at 2.00 m from a sphere of radius R = 2.00 cm carrying a charge of 25 μC. How fast will the small charge be travelling when it is 1.00 m from the sphere? Ignore gravity.

Two fixed point charges of q₁ = 3.0 μC and q₂ = 4.0 μC are situated at the opposite corners of a rectangle as shown below. The short side has length L = 0.25 m. Find the total potential at points A and B. If a free particle of charge q_f = 1.0 μC and mass M = 15 g has speed v_A = 2.50 m/s at point A and it follows the indicated path, what will be its speed at point B?
Two fixed point charges, q₁ = 3.0 μC and unknown charge q₂, are situated at the opposite corners of a rectangle as shown below. The short side has length L = 0.25 m. If a free particle of charge q_f = 1.0 μC and mass M = 15 g has constant speed v_A = 2.50 m/s as it follows the indicated path from A to B, what is q₂?
A metal sphere of radius 15.0 cm carries charge Q₁ = 12 μC. A second sphere of radius 5.00 cm carries a charge Q₁ = −8 μC. What will be the final charge on each sphere when they are connected by a metal wire?
There are three identical metal spheres, A, B, and C. Sphere A carries a charge of +5q. Sphere B carries a charge of -q. Sphere C carries no charge. Spheres A and B are touched together then separated. Sphere C is then touched to sphere A and separated from it. Lastly, sphere C is touched to sphere B and separated from it. How much charge ends up on sphere C?