Download Part I Directions

5.04: ELECTRIC FIELDS AND FORCES
Part I Directions
1. Your challenge is to get the positive test charge into the goal on the right of the
screen. On the top right of the screen you have a bucket of charges you may use to
“move” the test charge. On the bottom of the screen you have numerous options,
including the ability to “see” the electric field. Go ahead and press the “Field” checkbox
to turn this option on. Have the applet set to practice.
2. Using just positive (+) charges, arrange them in the playing area to get the test charge
into the goal. Once you are successful, reset the applet. Take note of how the positive
test charge and the other positive charges react with each other, and also notice the
direction and strength of the electric field.
3. Using just negative (-) charges, arrange them in the playing area to get the test charge
into the goal. Once you are successful, reset the applet. Take note of how the positive
test charge and the other negative charges react with each other, and also notice the
direction and strength of the electric field.
4. Now try using numerous charges, both positive and negative, to get the positive test
charge into the goal. Again, take note of how the positive test charge and the other
charges react with each other, and also notice the direction and strength of the electric
field between the charges.
5. Ready for a challenge? Increase the difficulty and see how good you are as an electric
field hockey player!
6. Use your observations and notes from the game to answer the questions below. Save
your answers to these questions, as they will be submitted at the end of this lesson. Be
sure to label them "Part 1."
Part 1 Questions:
1. What happened to the test charge when brought near another positive charge, and how
did you use this fact to score a goal only using positive charges? Explain for both the
practice charge and more difficult levels.
2. What happened to the test charge when brought near a negative charge, and how did
you use this fact to score a goal only using negative charges? Explain for both the
practice charge and more difficult levels.
3. After observing the electric field in your trials above, where was the electric field the
strongest? What was the direction of the electric field?
4. Did you notice an arrow appear as the test charge started to accelerate? This arrow
represented the electric force! If not, take another “shot” at the game above and come
back to this question. When was the electric force the greatest?
Part II Directions
1. Review Coulomb's Law.
2. Complete the short Electric Field Tutorial below. Solve the problems using the
information you learned from the tutorial.
3. Save your answers and be sure to label them " Part 2." Add this work to the answers
from Part 1.
Tutorial:
1. According to Faraday, a test charge can experience an electrostatic force due to the
presence of another charge or combination of charges. This force per charge (F/q) is a
very important quantity in the study of electricity. It is called the electric field.
2. The electric field that exists at a point can be calculated using the following equation:
E = F/q
E = the electric field
F = the electrostatic force experienced by a charge
q = the magnitude of the electrical charge
If the electrostatic force is expressed in Newtons (N) and the charge magnitude is expressed in
Coulombs (C), then the SI unit for the magnitude of the electric field is Newtons/Coulomb
(N/C). The electric field is a vector quantity requiring a direction for a complete description. The
direction is the same direction as the force on a positive test charge.
Part 2 Questions:
1. Discuss the symmetry between the laws of Charles Coulomb and Sir Isaac Newton
regarding forces.
2. Matt forgot to put the fabric softener in the wash. As his socks tumbled in the dryer,
they became charged. If a small piece of lint with a charge of +1.25 E -19 C is attracted
to the socks by a force of 3.0 E -9 N, what is the magnitude of the electric field at this
location?
3. Suppose an electric field with a magnitude of 2.8 E 4 N/C at a certain location, points
due south. If a charge of -4.0 E -6 C is brought to the location, what is the electrostatic
force that acts on this charge?
4. Think back to Coulomb's Law. Two coins with identical charges are placed on a lab table
1.35 m apart.
A. If each coin experiences a force of 2.0 N because of the presence of the other
coin, calculate the charge on each coin.
B. Would the force be classified as a force of attraction or repulsion? Explain your
answer.