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ELECTRICITY CHAPTER 1 ELECTRIC CHARGE • Charges Exert Force • Atoms are composed of particles with ______. The law of electric charges states that like charges _____and opposite charges _______ THE FORCE BETWEEN PROTONS AND ELECTRONS • Protons and electrons have ________ charges, they are ________ to each other THE ELECTRIC FORCE AND THE ELECTRIC FIELD • _____________ the force of attraction or repulsion on a charged particle that is due to an electric field • ____________ – the space around a charged object in which another charged object experiences an electric force CHARGE IT! Friction • ________- occurs when electrons are “wiped” from one object to another Conduction • __________ – electrons move from one object to another by direct contact. CHARGE IT! • _________ – charges in an uncharged metal object are rearranged without direct contact with a charged object CONSERVATION OF CHARGE • When you charge something by any method, ____________________________________. The numbers of ________ and _______ stay the same. • Detecting Charge • You can use a device called an _____________ to see if something is charged MOVING CHARGES • __________- a material in which charges can move easily • Examples: • __________- a material in which charges cannot move freely • Examples: STATIC ELECTRICITY • _________________ electric charge at rest; produced from friction or induction • _________________ – the release of electricity stored in a source 1.2 ELECTRIC CURRENT & ENERGY • _______________ – rate at which charges pass a given point • When you flip a switch, an _____________ is set up in the wire at the speed of light. The electric field causes the _________ in the wire to move. • This electric field is created so quickly that all electrons start moving through the wire _________. • Think of the electric field as a command to the electrons to charge ahead. TYPES ELECTRIC CURRENT Direct Current (DC) • ___________________ – charges always flow in one direction. • Ex: Alternating Current (Ac) • ___________________ – charges shift from flowing in one direction to flowing in the reverse direction • EX: VOLTAGE AND ENERGY • _______ – the potential difference between points • SI unit : • You can think of voltage as the amount of energy released as a charge moves between two points in the path of a current. • As long as there is a voltage between _________, charges will flow in the wire. The ____ of the current depends on the _______ Varying Nature of Voltage • Different devices need different levels of voltage. 1.5 V 9V 12 V Resistance • ___________ – opposition to the flow of electric charge • SI unit: • Good conductors, such as copper, have _____________ • Poor conductors, such as iron, have ______________ • Resistance depends on thickness, length, & temperature • Thick, _____ wires have ____ resistance than ____, thin wires. • The resistance of metals _________ as temperature _________ Resistance Generating Electrical Energy • Remember energy is not created or destroyed – it only changes forms • Parts of a Cell • A cell contains a mixture of chemicals called an __________. Every cell also has a pair of __________made from conducting materials Types of Cells • There are 2 types of cells: • ___ – have an electrolyte • Example: batteries – sulfuric acid is the electrolyte • ___ – have a dry electrolyte • Example: small radios or flashlights Generating Electrical Energy • Cells change chemical or radiant energy into electrical energy. Batteries are made of one or more cells. • ____________ can take thermal energy and transfer it to electrical energy. • _________convert light energy into electrical energy. 1.3 ELECTRICAL CALCULATIONS • How fast is a nanosecond? A nanosecond (ns) is one-billionth of a second. Electrical signals travel at 30 cm/ns. Calculate how far electrical signals travel in 1 second. • CONNECTING CURRENT, VOLTAGE, AND RESISTANCE • Georg Ohm Ohm (1789 –1854) studied the resistance of materials. He measured the current that resulted from different voltages applied to a piece of metal wire. Electric Power • Ohm’s Law – the ratio or voltage (V) to current (I) is the resistance (R) of a material • V=IxR Unit SI Unit Voltage (V) V - volt Current (I) A- Amps Resistance (R) Ohm - Ω OHM’S LAW CALCULATIONS • Ex: 1 What is the voltage if the current is 2 A and the resistance is 12 Ω ? • Ex: 2 Find the voltage if the current is 0.2 A and the resistance is 2 Ω OHM’S LAW CALCULATIONS • Ex 3: The resistance of an object is 4 Ω. If the current in the object is 9 A, what is the voltage used? • Ex 4: An object has a resistance of 20 Ω. Calculate the voltage needed to produce a current of 0.5 A. ELECTRIC POWER • Electrical Power (P) – the rate at which electrical energy is converted into other forms of energy • Si Unit: Watts (W) • Power = voltage x current • P=VxI Unit SI Unit Voltage (V) V - volt Current (I) A- Amps Power (P) W - Watts ELECTRICAL POWER CALCULATIONS • Ex 1: A toaster draws approximately 10 A of current. A home receives 120 V at each electrical outlet. What is the power of the toaster? • Ex 2: A car uses a 12 V battery. One headlight draws 3.0 A. What is the power of the headlight? ELECTRICAL POWER CALCULATIONS • EX 3: A light bulb draws a 0.5 A current at a voltage of 120 V. What is the power rating of the light bulb? ELECTRICAL ENERGY • Measuring Household Energy Use • Different amounts of electrical energy are used each day in a home. Electric companies usually calculate electrical energy by multiplying the power in kilowatts by the time in hours. 1.4 ELECTRIC CIRCUIT • Just like a roller coaster, an electric circuit always forms a loop— it _____ and ____ at the ____ place • Parts of an Electric Circuit • • • (light bulb, appliance) SWITCHES • Sometimes, a circuit also contains a _____ • _____ – opens or closes a circuit • _____ – electrons can ____ • _____ – electrons _____________ TYPES OF CIRCUITS • ______________– a circuit in which the parts are joined one after another such that the current in each part is the same. • _________for charges to follow – charges must flow through each part of the circuit • The voltage across each load is _________ Series circuits are useful in wiring burglar alarms. If any part of the circuit fails, there will be __________in the system and the alarm will sound. TYPES OF CIRCUITS • _______________- a circuit in which the parts are joined in branches so that the voltage (potential difference) across each part is the same • Loads do ___have the _________________ • Charges have more than ___ path to follow Parallel Circuits are used in almost all appliances and decorative string lights HOUSEHOLD CIRCUIT SAFETY • Circuits can ____ if they are __________ or a wire breaks or has water damage. • To prevent fire: • • A thin strip of metal in circuit that the charges flow through. If the current is too high, the metal will melt and the circuit is broken • • A switch that automatically opens if the current is too high. A metal strip heats up, bends, and opens the switch stopping the flow of current