Electricity Chapter 6

6-1 – Electric Charge Positive & Negative Charges Remember the structure of the atom When we charge something, we transfer electrons Static electricity – Law of Conservation of Charge – When we charge something, we transfer electrons, electrons are not created or destroyed

6-1 – Electric Charge Charges Exert Forces Like charges repel Opposite charges attract Force of charge depends on – Amount of charge – Distance between charges

6-1 – Electric Charge Charges Exert Forces Like charges repel Opposite charges attract Force of charge depends on – Amount of charge – Distance between charges Electric Field-

6-1 – Electric Charge • Electric Field- • Comparing electric forces to gravitational forces – In atoms and molecules, electrical forces are enormous – In objects around you, much less, but transfer of the slightest charge can be noticed

6-1 – Electric Charge Conductors & Insulators – Conductor (outmost electrons are loosely bound) – Insulator (outermost electrons are tightly bound)

6-1 – Electric Charge Charging by Contact – Objects must touch • Charging by Induction – Objects do not have to touch, just be near each other

6-1 – Electric Charge Lightning – Thunder – sound produced by the lightning – Grounding

6-2 - Electric Current Electric Current - Electrons flow in a way similar to water The rate if flow of electrons is measured in ampere

6-2 - Electric Current • Why does current flow?? • Electrons will flow in a wire only when there is a difference in electrical pressure • Voltage difference – • Voltage is directly proportional to electrical pressure • Voltage = potential energy/charge

6-2 - Electric Current • Electric circuits – • Current and electron flow – Current is in the direction of positive charge flow – Electron flow is negative charges moving – Current and electron flow will be in opposite directions

6-2 - Electric Current Steady current requires a pump (chemical batteries or generators) Batteries & Wall Outlets

6-2 - Electric Current Electrical resistance – Factors that affect resistance – Length or wires – Kind of material – Temperature Resistance is measured in ohms

6-2 - Electric Current Current(amp) = voltage(volts)/resistance(ohms) Ohm’s Law - relationship between current, voltage, and resistance Current is directly proportional to voltage Current is inversely proportional to resistance Current(amp) = voltage(volts)/resistance(ohms)

Let’s Practice!!!! What is the current in a 120V circuit if the resistance 20Ω? What is the current in a 120V circuit if the resistance 5Ω? What voltage is required to move 2A through 5Ω? What is the resistance of a circuit with 20V and 2A?

6-2 - Electric Current • Direct current – Electrons that flow in one direction – Batteries produce direct current – Current moves from negative to positive • Alternating Current – Electrons flow initially in one direction then in the opposite direct – Generators create alternating current by switching the signs of the terminals which alternate back and forth

6-3 - More Complex Circuits Series Circuits Parallel Circuits Open Circuits

6-3 - More Complex Circuits • Household Circuits – Safety Devices • Fuses • Circuit breakers

6-3 – More Complex Circuits • Electrical Power and Energy – Moving charges can do work P = IV power (watts)= current (amps) x voltage (volts)

Let’s Practice!!! A toaster oven is plugged into an outlet where the voltage difference is 120 V. How much power does the toaster oven use if the current in the oven is 10 A? A flashlight bulb uses 2.4 W of power when the current in the bulb is 0.8 A. What is the voltage difference supplied by the batteries? A blender uses 3.4 W of power when plugged into a 120V outlet. What is the current of the blender?

6-3 – More Complex Circuits • Electrical Power and Energy – Can also be calculated in electrical energy E = Pt

Let’s Practice!!! A toy uses 400 W in 45 seconds. How much power was used? A cell phone charger uses 5 000 W in three hours. How much energy was used? A light bulb uses 75 watts and is turned on for 1.5 hours. How much power was used? If a portable phone needs two watts to operate and it is used for 15 seconds, how many joules will have been used?