Electric Circuits Conventional Current Flow Ohms Law Electricity

Electric Circuits Conventional Current Flow & Ohm’s Law

Electricity Water Analogy

Current Electricity • Electrostatics: Non-moving electricity • Current Electricity: Moving electricity Electric Current • Flow of charge (usually electrons) in a conductor (usually metal) past a point in one second • Measured in Amperes (A) I = Current (A) Q = Charge (C) t = Time (s)

Current Electricity Example: My 50 A speaker is going full blast for 20 minutes, how many electrons pass through it? • I = Q/t • Q = I*t • Q = (50 A)(20 min)(60 s/min) • Q = 6 x 104 C • Q = N*e • N = Q/e • N =(6 x 104 C)/(1. 6 x 10 -19 C/electron) • N = 3. 75 x 1023 electrons

Current Electricity Electrons Do Work Electron Flow What actually flows? • Electrons: + • What truly happens + • Protons - hard to move + • Electrons - easy to move • Positive Charge: • Historically what people thought We are using Conventional • Conventional Current Flow • Assume current flows out of the positive terminal Positive Charge

Ohm’s Law Current Does the battery care ΔV what we hook up to it? • No, Voltage stays the same + + What affects the amount of + current flowing? • Voltage of battery • Size of resistances hooked up to the battery Ohm’s Law I = Current (A) V = Voltage (V) R = Resistance (Ω)

Ohm’s Law Example: What current will flow from a 6. 0 V battery when a 50. 0Ω light bulb is attached? • V = I*R • I = V/R • I = (6. 0 V)/(50. 0Ω) • I = 0. 12 A

Ohm’s Law Example: What is the minimum resistance a 120 V house circuit with a 15 A breaker can withstand? • V = I*R • R = V/I • R = (120 V)/(15 A) • R = 8Ω If we hooked the same resistance to a 240 V dryer plug, will its 15 A breaker turn off? • I = V/R • I = (240 V)/(8Ω) The circuit breaker will open because 30 A > 15 A • I = 30 A