Ohm’s Law & Electrical Power

Resistance - the tendency for a material to oppose the flow of electronsResistance - the tendency for a material to oppose the flow of electrons - All materials have some electrical resistance. - Resistance depends on length, cross- sectional area, material, and temperature Ex. Making wires thinner, longer, or hotter increases the resistance. Resistance

Resistors provide a specified amount or resistance to a conductor. Used to regulate the amount of current in a conductor. Resistors

Ohm’s law - the current in a circuit (I) equals the voltage difference (V) divided by the resistance (R). R = V/I Resistance is measured in ohms . Ohm’s Law

Sample Problem The resistance of a steam iron is 19.0 Ω. What is the current in the iron when it is connected across a potential difference of 120 V? R = V/I V= 120 V R= 19 Ω I = V/R = 120 V / 19 Ω = 6.32 A

Electrical Power Electrical Power is the rate at which electric charge converts electrical potential energy to non-electrical forms of energy. P = IΔV = I²R = ΔV²/R SI Unit = watt (W)

Sample Problem An electric space heater is connected across a 120 V outlet. The heater dissipates 1320 W of power in the form of electromagnetic radiation and heat. Calculate the resistance of the heater. V= 120 VP = 1320 W P = ΔV²/R R = ΔV²/P = (120 V)²/ 1320 W = 10.9 Ω

Electric Power Electric companies measure energy consumed in kilowatt-hours (kW h)

Electric Power How much does it cost to operate a W light bulb for 24 h if electrical energy costs $0.080 per kWh? Total Energy Used = (0.100 kW)( 24 h) = 2.4 kWh Cost = (2.4 kWh)($ 0.080/ kWh) = $0.19