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

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

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

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

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.

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

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

Factors that affect resistance

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