Preview - Charge Interactions Chem/Phys

Combining our Three Equations together into One!

Now we will look at what we found for how each of the three independent variables (charge_1, charge_2, and separation) relate to the overall force. We will try to make sense of it all.

Remember that when we linearize, the value (and units!) of the slope and intercept are important. We can use our 5% rule to see that for the most part, we shouldn't have a y-intercept for any of the equations.

Referenced Questions

These questions were answered in the previous steps. They are provided here for your reference.

Let's now find a mathematical relationship between charge_1 and force.  

Is this data linear? If so, we can click on the graph, then click on the ruler tool, then on the "least-squares line". This will draw a best fit line through your (linear) data. You can then write a mathematical model that describes the line. Remember to use the actual variables, not x & y, and to determine what the units must be for slope and intercept.  Write your mathematical model in the answer box.

If your original data was not linear, follow the procedure listed below the simulation to linearize your data with CODAP.

Now use your simulation and CODAP to write a mathematical model that describes the relationship between charge_2 and force.  Use the same process as you did in question 2.3 above to linearize your data if necessary.  Write your mathematical model in the space below.

Now use your simulation and CODAP to determine write a mathematical model that describes the relationship between force and separation. Use the same process as you did in 2.3 above to linearize your data if necessary. Write your mathematical model in the space below.

Questions

Please answer the questions below.

Let's look at the three relationships we determined on the last page:

  1. Force is directly proportional to both charge_1.
  2. Force is directly proportional to charge_2.
  3. Force is inversely proportional to the square of separation.

Knowing this, let's write one proportion that says how force relates to all three of these variables. 

Hint - we did something similar with Gravity not too long ago!

Our proportion with all the variables isn't an equation because on one side we have force which is in Newtons but on the other, we have charge_1 * charge_2 (in Coulombs2) and separation2 (in meters2). Those units aren't equal to each other!

This inconsistency means we need a constant of proportionality, which we will call k. Rewrite your proportion as an equality using k.

Hint - when we studied gravity we did something similar. We called that constant G and wrote it in front of all of our variables, like 

F = G*(our proportionality). See if you can do the same thing with the electric force but use k instead. Write your complete equation in the answer box below!

Now we are ready to find that constant of proportionality, k. Use the simulation to record one trial. Plug in the values of the force, both charges, and separation, and see if you can solve for k. We are looking for the value of k and also its units. Record your answer in the box below question 3.4.

What value did you determine for the constant, "k" in the equation? Be sure to report a value AND appropriate units!

Notes

These notes will appear on every page in this lesson so feel free to put anything here you'd like to keep track of.