CURRENT VOLTS AND RESISTANCE OHMS LAW COULOMB Recall

CURRENT, VOLTS AND RESISTANCE (OHM’S LAW)

COULOMB • Recall that one Coulomb has 6. 25 X 1018 electrons. • If the current coming out of the outlet on the wall has 600 C, how many electrons are coming out of the outlet? 1 C = 6. 25 X 1018 electrons 600 C #e. Cross multiply and you get 3. 75 X 1021 electrons

CURRENT INTENSITY Symbol: I Units: Amperes, A • Current Intensity - the amount of electrons that flow past a given point in a circuit every second (i. e through a wire) • Example: 0. 7 amperes is shown by I = 0. 7 A • An ammeter is the instrument used to measure A current intensity

CURRENT INTENSITY • The current intensity in a circuit can be determined using the formula: I = q/t I is the current intensity in amps (A) q is the charge in coulombs (C) t is time in seconds (s) NOTE: 1 Amp (A) = 1 Coulombs (C)/1 second (s) A=C/s

EXAMPLE #1 What is the current flowing through a car headlight if there are 900 C of charge used in 1 minute? I = q/t I = 900 /60 I = 15 A

EXAMPLE #2 How much charge does it take to operate an MP 3 player for 15 minutes if the current is 2 A? I = q/t 2 = q/900 q = 1800 C

POTENTIAL DIFFERENCE Symbol: (VOLTAGE) V Units: Volts, V • Potential Difference is the amount of energy transferred between two points in an electrical circuit. It is the voltage that is measured at a load. • Example: Energy that is provided by a battery or power supply. It could be a 12 volts battery (also know as 12 V) • V A voltmeter is used to measure potential difference

POTENTIAL DIFFERENCE (VOLTAGE) • The potential difference can be determined using the formula: V=E/q V is potential difference in volts (V) E is the energy in joules (J) q is the electric charge in coulombs (C) Note: 1 Volts = 1 Joule / 1 Coulombs V=J/C

EXAMPLE #3 • In a house, how much energy is provided by 120 V service providing 200 C of charge? V=E/q 120 = E/200 E = 24 000 J

RESISTANCE Symbol: R Units: Ohms, Ω • Resistance is how difficult it is for current to flow • Resistance analogy: imagine a river flowing. If you put a large boulder in the river, the current on the other side of the boulder will slow down. If you put a small boulder in the Conductor Resistor– river, the current on the other side of the(wire) boulder-will still be high resistance quick. Now replace&river flow with low flow resistance of electrons, &and a low current flow high current flow boulder with a resistor. • A resistor is used to slow current down and convert electrical energy into heat energy (e. g. light bulb, stove element).

OHM’S LAW • Ohm’s Law states – that for a given resistance, the potential difference in an electrical circuit is directly proportional to the current intensity.

FORMULA TO SOLVE CIRCUITS • Resistance, current intensity and potential difference are all related R = V/I R is the resistance in Ohm’s (Ω) V is the potential difference (Volts) I is the current intensity (Ampere) Note: 1 Ohms= 1 Volts / 1 Amper 1 (Ω) = 1 V / 1 A

EXAMPLE #4 • An stove element 30 Amperes going through it, and carries 120 volts of electricity, how much resistance is in this circuit? • R = V/I • R = 120 V/30 A • R = 4 V/A = 4 Ω

EXAMPLE #5 • A circuit has a potential energy difference of 240 V and offers a resistance of 6Ω, what is the intensity of the current flow? • R=V/I • 6 = 240 /I • I = 240 /6 • I = 40 A

EXAMPLE #6 • A circuit has a resistance of 10Ω & a current intensity of 5 A. What is the potential difference? • R=V/I • 10 = V/ 5 • 10 X 5 = 50 V

SUMMARY TABLE Resistance Current Potential Difference Definition Slows current down The flow of electrons Causes electrons to flow Symbol R I V Units Ohms (Ω) Amps (A) Volts (V) I=q/t A=C/s V=E/q V=J/C Ammeter or formula Voltmeter or formula Formula (if applicable) How measured (if applicable) R=V/I Ω=V/I Circuit Formula

ASSIGNMENT • Page 319 – Questions 1 – 11 • Handout