Unit 17: Electric Charge & Fields

Practice Problems

Note: problem difficulty is ranked using a star system.

  • (*) One-star problems are fundamental to the unit, and can be done relatively quickly. Use these problems to introduce yourself to the material.

  • (**) Two-star problems are more difficult, and require an understanding of one or two key concepts. Use these problems to test your understanding of the material.

  • (***) Three-star problems are the most difficult, and require some creative thinking in addition to a deep familiarity with multiple key concepts. Use these problems to challenge yourself; if you can complete one of these, you’re on your way to mastering the material.

*Q17.1) Write the charge (in Coulombs) of the following things:

a) A chlorine ion

b) A calcium ion

c) A sodium chloride molecule

*Q17.2) You rub a balloon on a wall until the balloon has a total charge of -10 C. How many electrons did the balloon gain?

*Q17.3) Find the magnitude and direction of the electric field produced by a calcium ion at a point 20nm away from it.

***Q17.5) A calcium ion and a potassium ion are separated by 50nm. Where (if anywhere) will the electric field have a magnitude of 0?

**Q17.4) A calcium ion and a chlorine ion are separated by 50nm. Find the magnitude and direction of the electric field at the midpoint between them.

***Q17.6) A calcium ion and a chlorine ion are separated by 50nm. Find the magnitude and direction of the electric field at the point P shown below:

***Q17.7) Four charges are located at the corners of a square of sidelength 1m as shown below. If q = 1C, find the magnitude and direction of the electric field at the point P at the center of the square.