How about a short assignment for a short week:

Read chapter 34

1. Why don't the birds on the powerlines of the first page get electrocuted?

The entire wire is at the same potential (for practical purposes at least, over the distance spanned by the bird's feet). The risk of injury is owed to potential difference -- if the whole wire is 5000 V then each foot is at 5000 V and the all important ∆V is 0. Note that should the bird contact a tree or pole that is grounded (V = 0) -- fricassee by electrocution!

2. Imagine that you could get so small that you could enter the metallic crystal lattice of a piece of copper wire. Imagine that an electron could be "seen" by an observer of that size. What would you "see" if the wire that you were in experienced a positive potential to your left and a negative potential to your right?

An electric current exists in a metal because electrons move from a negative potential to a positive potential. You would "see" electrons traveling towards you from your right and moving away from you on your left. Because copper is a pretty good conductor, those moving electrons would move along quite smoothly, only occasionally experiencing interference resulting from collisions with copper atoms.

3. What has more resistance -- a wire of .001 m in radius or a wire of .0005 m (half the radius) -- assume each is one meter in length?

Resistance is less with a larger cross-section to travel through. The thin wire has more resistance.

4. What has more resistance -- a wire of .001 m radius and 1 meter of length or a wire of .001 m radius and 5 meters of length?

Resistance is greater, the greater the length. The 5 meter long wire has a greater resistance.

5. What is the resistance where a 2 Amp current is driven by 12 V of potential difference?

R = ∆V÷I = 12 V ÷ 2 A = 6 Ω

6. What is the potential difference where 3 A is driven through a 5 Ω resistor?

∆V = I • R = 3 A • 5 Ω = 15 V

7. What current does a 12 V battery produce in a 6 Ω resistance?

I = ∆V ÷ R = 12 V ÷ 6Ω = 2 A