Download The ultimate worksheet for “The Big Four”

The ultimate worksheet for “The Big Four”
There are three basic cases for the “Big Four,” and it may be wise to write the “Big Four” down
here:
1. _________________________
and equation: _______________________
2. _________________________
and equation: _______________________
3. _________________________
and equation: _______________________
4. _________________________
and equation: _______________________
Let’s examine the cases…
Case 1—A point charge in space
The Cartesian coordinate system represents space. Use a blank sheet of paper or graph paper to
represent this space. The scale of the x-y axis is 1 unit = 10 cm. You now have an object with a
charge of +Q placed at the fixed position (2, 1). Q can be any number. For this example, let it
be +3 mC.
a) Your charge is positive, which means there are more ____________ than
_____________.
b) Calculate “roughly” how many more there are: _______________ (hint: possible MCq)
work:
c) For all points in this space, one can only calculate the ________________ and the
________________ due to this “Case 1” point charge.
c) One of these is a vector, and the other is a scalar. Which is which?
The ________________ is the vector and _________________ is the scalar.
d) Now, determine the vector choice from c at point (-1,3). Show all work. Don’t forget, this is
a vector. Hint: This can be done by hand. Anything “by hand” is fair game for MC.
Thought from ‘d’: does this problem get a lot or a little harder if you start with multiple charges?
e) Determine the scalar choice from c at point (-1, 3). Show all work. Don’t forget, this is a
scalar.
Thought from ‘e’: does this problem get a lot or a little harder if you start with multiple charges?
Now let’s examine the other two of the “big four”:
f) The result from d represents the ___________________________________________ if a
charge is placed at point (-1,3).
g) The result from e represents the amount of _____________________________________
if a charge is placed at point (-1,3) from the position _________________.
f) Use one of your values (from ‘d’ or ‘e’) to easily answer these questions:
How much potential energy would a proton have if placed at (-1,3)? ________________
Work:
What would be the initial acceleration (vector) of an electron if placed at (-1,3)? _____________
Work:
Case 2—Two conducting plates separated by a distance 2mm
Square plates: 2cm by 2 cm
Attach a 6 Volt battery to the plates. Make the right
side of the battery positive.
a) What does the battery “do” to the available charge on
the conducting plates? The battery puts the _____________
into a higher __________________.
b) At first is it easy or hard to move the electrons?
c) After some time, is it easy or hard to move the electrons? Explain.
d) How could one go about “discharging” the plates?
e) Sketch current vs. time (qualitative) when charging and then discharging the plates.
Current vs. time (charge)
Current vs. time (discharge)
f) Calculate the value and sketch the direction of the E-Field inside the plates when they are fully
charged.
g) Sketch a few equipotential lines inside the plates.
h) The values of the equipotential surfaces go from ____________ to _____________ when
moving along the direction of the E-Field.
i) What is the rule when an E-Field line and an equipotential surface line intersect?
Rule:
j) The plates arranged as such is called a _______________ because it can store both
___________ and ___________.
k) If the surfaces of the plates increase, what happens to the amount of charge that can be stored?
Explain.
l) If the distance separating the plates changes, does it affect the E-Field? The amount of charge?
m) Calculate the capacitance of the capacitor. Can you estimate this by “hand”?
n) Calculate the charge stored on the plates. What is the net charge on the plates?
o) How much energy is stored on the plates?
p) If you had capacitors in series and in parallel, and each had the same battery connected, which
would have a greater amount of stored energy?
Practice: Equivalent Capacitance for the 2 arrangements below:
Current and Resistance:
a) Current is the flow of ___________________ per __________________.
For a given material used in making a resistor...
b) If the length of the resistor increases, its resistance ____________ and current flowing
through it would ____________.
c) If the cross-sectional area of the resistor increases, its resistance ____________ and current
flowing through it would ____________.
d) If the temperature of the resistor increases, its resistance ____________ and current flowing
through it would ____________.
e) What is “Ohmic”?
Be able to sketch V vs. R, V vs. I, R vs. I, and know what the slopes of each (if applicable)
represent. In the 3rd case, how could you make it a linear relationship?
f) If you connect a 200 Ohm resistor with a 6 volt battery, how much current would flow?
g) Roughly, how many electrons is this “per second”
h) Given 2 batteries, how would you arrange them to get the most voltage?