Current, Resistance Chapter 24 24.1Current 24.2Conductivity and Resistivity 24.3Resistance and...

Current, Resistance Chapter 24

24.1 Current

24.2 Conductivity and Resistivity

24.3 Resistance and Ohm’s law

24.4 Electric power

Question: When you turn the ignition key in the car, you complete a circuit from the negative battery terminal through the electric starter and back to the positive terminal. This is a DC circuit and electrons migrate through the circuit from negative to positive terminal. About how long must the key be in the ON position for electrons starting from the negative terminal to reach the positive terminal?

A. A time shorter than the human reflex turning a switch on or off

B. ¼ second

C. 4 seconds

D. 4 minutes

E. 4 hours Answer: about 4 hours

Without electric field

With electric field

Why does the light come on at once if vd is so small?

24.1 Current, drift velocity and current density

0.28 mm/s - but they all start moving at once

24.2 Conductivity and Resistivity

The presence of electric fields in conductors results in electric current

No longer have electrostatic equilibrium

Collisions oppose the electric force, and the electric field sustains a steady current

Answer: No

No voltage difference across its body, no current flows

24.3 Resistance and Ohm’s Law

defines R for any conductor

VR

I

Now will the bird get…. ?

24.4 Electric Power

Answer: D

It consumes the most energy per second (power)

Answers: B

An electric motor consumes energy, not electricity.

A generator generates electric energy