2- Ohm’s law and Power

The total amount of charge that passes through a wire at any point per unit time is referred to as : 1) current 2) electric potential 3) voltage 4) wattage

The direction of convention current is the direction that : 1) negative charges would flow 2) positive charges would flow 3) electron flow

How is eclectic power calculated? Electric power used by a device is equal to the current times voltage: P = I V ( SI unit W)

Car outlets ( used to charge your cell phone) s may be rated at 20 A, so that the circuit can deliver a maximum power. A car batter has 12 V. What is the power ? P=IV P=IV= (20 A) (12 V)=240 W electric power may be expressed as volt-amperes or even kilovolt-ampere 1 kA ⋅ V=1 kW

Electrons move slowly through wires

Potential difference drive electron through a wire Ohm’s law relates the applied potential difference to the current produced and the wires resistance.

Applied voltage(V) = current (I) x resistance(R) V=I R R = V / I SI unit: Ohm ( Greek letter Omega) Ω 1 Ω = 1 V/ 1 A

Resistance Collisions between electrons and atoms in the wire cause a resistance to the electron’s motion. Analogy example --- Friction of resisting the motion of a box sliding across a floor Or dense crowd reducing your waling speed

Resistor –small device used in circuits to provide particular resistance to current ( can represent resistance of a wire or device)

A potential difference of 24 - V is applied to a device that has a resistance of Ω. How much current flows through the resistor?

I = V/R = 24 V / 150 Ω =.16 A

Power (P) is the rate at which energy (PE) is moved P = PE / t PE = q V = q V/ t I = q / t P = I V

Ohms law V=IR for electric power Apply ohms law to V=IR P = power P = I V = I ( I R) = I 2 R Apply ohms law to V=IR P= power P = I V = ( V/R) V = V 2 / R

3 valid power equations Form Ohms law V=IR P = IV P= I 2 V P=V 2 R

A 12 V battery is connected to a device that has 570 Ω resistance. How much energy is dissipated in the resistance in 65 s ?

Known: Voltage = 12 V Resistance (R) = 570 Ω Δ t = 65 s ΔPE = ? P= V 2 / R =(12 V) 2 / 560 Ω =.25 W ΔPE = P (Δ t) = (.25 W) (65 s) = 16 J

What's this symbol called Ω ?