1. Ch 17 Electrical Energy and Current
17 – 3 Current and Resistance

2. Current is the Rate or Charge Movement
Current: the rate at which electric charges pass through a given area.
SI unit = Ampere
1 A = 1C/s
I = current
Q = charge
t = time interval

3. Sample Problem
A charge of 1.67 C goes through a filament of a certain light bulb in 2.00s. Determine the current in the light bulb.
Given: ∆Q = 1.67, ∆t = 2.00s
Unknown: I = ?
I=∆Q/∆T
I= 1.67C/ 2.00s
I= .835A

4. Conventional Current
Positive and Negative charges in motion are sometimes called charge carriers.
The direction of conventional current is defined as being in the direction of the movement of positive charge carriers

5. Drift Velocity
The drift velocity = the average velocity that a particle attains due to an electric field.
In general, an electron will rattle around in a conductor at the Fermi velocity randomly.
An applied electric field will give this random motion a small net velocity in one direction.

6. Drift Speeds are Relatively Small
Magnitudes of drift velocities, or drift speeds are very small.
Drift speeds are typically smaller than the average speed between collisions.
Ex: If a copper wire that has a current of 10.0 A, the drift speed of electrons is only 2.46E-4

7. Resistance to current
Resistance is the opposition to the motion of charge through a conductor.
SI Unit = Ohm
Symbol = Ω
1 Ω=1 volt/Amp

8. Factors that affect resistance

9. Ohm’s Law
Applies to materials that have a constant resistance over a wide range of applied voltage.
V = I R