Chapter 17.3 – Circuits electric circuit – a set of electrical components connected such that they provide one or more complete paths for the movement of charges open circuit – when there is no complete path for the charge to flow through closed circuit – when there is a complete path across a source of voltage allowing charge to flow

Chapter 17.3 – Circuits switch – device used to open or close a circuit ex. light switch schematic diagram – a graphical representation of a circuit that uses line to represent wires and different symbols to represent components

Chapter 17.3 – Circuits wire resistor light bulb battery open switch closed switch you can draw any circuit using these symbols and others

Chapter 17.3 – Circuits 2 kinds of circuits series circuit – current has only one path to follow, the parts are joined one after the other so the current in each part is the same the voltage across each part is difference the resistances add up to get a total resistance: RT = R1 + R2 if there is an open switch then no current can flow through the circuit ex. in old Christmas lights, if one bulb burns out then the whole string goes dark

Chapter 17.3 – Circuits

Chapter 17.3 – Circuits 2. parallel circuit – contains separate branches for the current to go through, the voltage across each part is the same the current across each part is different resistors in parallel add inversely: 1 𝑅 𝑇 = 1 𝑅 1 + 1 𝑅 2 advantages: when a switch is opened in one branch, current still flows through the other branches in homes most circuits are parallel circuits resistors in parallel receive more current than resistors in series

Chapter 17.3 – Circuits

Chapter 17.3 – Circuits when wires carry more than a safe level of current the circuit gets overloaded the high current in overloaded circuits can cause fires if the insulation is worn down on a wire then the current may find an alternate path to the ground, called a short circuit fuse – electrical device that contains a metal strip that melts when current in the circuit becomes to great - used to prevent overloading in circuits

Chapter 17.3 – Circuits circuit breaker – a switch that opens a circuit automatically when the current exceeds a certain value uses a magnet or bimetallic strip that bends when the current gets too high and breaks the circuit ground fault circuit interruptor (GFCI) – special outlet that acts as a small circuit breaker used in bathrooms and kitchens

Chapter 17.3 – Circuits when a charge moves in a circuit the charge loses energy some energy is transformed into useful work some energy is lost as heat electric power – the rate at which electrical energy is converted into other forms of energy unit of power is the watt (W) also common to use kilowatts (kW)

Chapter 17.3 – Circuits power = current x voltage P = I∙V can derive other forms of the power equation using Ohm’s law P = IV = I2R = 𝑉 2 𝑅 electric companies charge for the energy used not power used keep track of kilowatt-hours (kW∙h) 1 kW∙h is the energy used in 1 hour at a rate of 1 kW use electric meters to record how much energy is used

Chapter 17.3 – Circuits A space heater draws 29 A of current when plugged into a 120 V outlet. How much power does it use? A color TV uses 320 W of power. If it is plugged into a 120 V outlet how much current runs through it?

Chapter 17.3 – Circuits In an iron the heating element draws 5.0 A of current. If it dissipates 590 W of power how much resistance is in the heating element? A graphing calculator uses a 6.0 V battery and uses 0.015 W of power. How much resistance is in the calculator?