1. 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

2. 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

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

4. 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

5. Chapter 17.3 – Circuits

6. 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 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

7. Chapter 17.3 – Circuits

8. 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

9. 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

10. 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)

11. 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

12. 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?

13. 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 W of power. How much resistance is in the calculator?