Physics 1100 In-Class Problems: Electrostatics

1. 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.





2. 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.

   

3. Where would you put a positive charge of +1 μC in the diagrams below so that the net electrostatic force on it is zero?



4. 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 Q₁ and Q₂.
   (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.

   

5. 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) is the tension in the string?
   (c) What is the magnitude of the unknown charge?

   

6. 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.

   

   

   

7. Find the net electric field at point A in the diagram below.



8. 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?

9. 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?

   

Questions?mike.coombes@kwantlen.ca