AP E&M – Current and Resistance
1. The density of protons in a solar wind is 8.7 protons per cubic cm and their speed is 470km/s.
a. Find the current density of these protons.
b. If these protons were to strike Earth (r = 6.38E6m), what would be the total current this planet would receive?
2. Assume the current generated from a car battery is 300A (to get it started). If the electrons travel through a copper wire with cross sectional area of 0.21 m2 and length of 0.85cm. How long does it take the electrons to get from the car battery to the starter? (assume the density of electrons in copper to be 8.47E28/ m3).
3. An iron cable has length 1.7 cm and diameter of 2 mm.
a. Determine the resistance of the cable (p=10.6E-8 Wm)
b. Determine the conductivity of the cable.
4. The resistance of a car speaker is 4W. The current flowing through the speaker is 30 amps.
a. How much power is output by the speaker?
b. If the speaker is replaced by a new speaker of 16 W, what is the new power output (assuming you up the voltage to maintain the same current)?
5. What is the power output of an electric frying pan that draws 15 amps and has a resistance of 8W?
6. If the resistance of your body were approximately 120,000 W:
a. How much current would run through your body if you were to touch both ends of a car battery (12V) at the same time?
b. Assume you have just gotten out of the pool, lowering your resistance to a mere 1500W, now how much current would run through your body?
7. A wire with length 2.6 m and diameter of 1.3 mm carries 5.1 amps of current. The wire dissipates heat at a rate of 78 mW.
a. What is the resistivity of the wire?
b. What is the conductivity of the wire?