Electrical Systems

Types of Circuits Series Circuit: a circuit where current only follows only one path Parallel Circuit: a circuit where current “branches off” in different directions

Types of Circuits Short Circuit: a circuit made with a parallel branch using only a wire

Series & Parallel Circuits Series Circuit Current is the same at all points All voltage drops add up to voltage of battery Total resistance increases with more resistors Parallel Circuit All currents add up to the total current of battery Voltage is the same at all points Total resistance decreases with more resistors

Series Circuit Series Circuit: current can only follow one path. All voltage drops add up to the voltage of the battery. The current in a series circuit is the same at any point. The total resistance increases as more resistors are added. R I V 1 Ω 0.25 A 0.25 V 2 Ω 0.50 V 3 Ω 0.75 V Total = 6 Ω Total = 0.25 A Total = 1.5 V

R I V Total =

R I V Total =

R I V Total =

Parallel Circuits Parallel Circuits: a circuit where current ‘branches off’ in different directions. All voltage drops are the same The current across each load adds up to the current supplied by the battery. Resistance decreases as more resistors are added. R I V 1 Ω 3 A 3 V 2 Ω 1.5 A 3 Ω 1 A Total = 6/11 Ω Total = 5.5 A Total = 3 V

R I V Total =

R I V Total =

R I V Total =

Combination Circuits A combination of series and parallel. Simplify resistors just in series or just in parallel Redraw simplified circuits until there is a single resistor

Determine the total resistance

Find the Total Resistance

Find the Total Resistance

Find the Total Resistance

Short Circuits Short Circuit (Short): a circuit made with a parallel branch using only a wire Bypasses a part of the circuit Increases the current through a circuit (less resistance) Electricity always follows the path of least resistance. Short circuits in homes can Waste energy Heat wires (melt the insulation or cause fires)

Which circuit below has a short in it?

Fuses A fuse prevents too much current from flowing through a circuit It “breaks” if the current is too high.

What Is Power?

Power Power: the amount of energy (work done) each second by a circuit. Measured in watts

Determine the amount of power the circuit below has.

How much current flows through a 70 watt guitar amp that runs on a voltage of 120 volts?

Additional Problems Determine the power used by a hair dryer that draws a current of 8 amps and runs on 120 volts of electricity. Determine the current used by an iPod that runs on a 3.7 V battery and has a power of 2 watts. Convert 200 cV to kV Convert 4.5 in/min to m/hr

Electrical Power at Home Electric meters measure kilowatt hours (kW·hr) A 1 kW appliance ran for 1 hour = 1 kW·hr Energy = P·t

An electric stove uses 3,000 watts of power An electric stove uses 3,000 watts of power. It is used to bake for 30 minutes. How many kilowatts of power does it use? How many kilowatt hours does it use while baking? If electricity costs $0.15 per kilowatt hour, how much does this cost?

A 100 watts light bulb is left on for 5.5 hours. How many kilowatts of power does it use? How many kilowatt hours does it use? If electricity costs $0.15 per kilowatt hour, how much does this cost?

DC and AC DC current AC current Direct current Current or voltage keeps the same direction AC current Alternating current Current or voltage reverses (60 times / sec in US)

DC and AC DC current is good for short distances AC can be converted to lower voltages or DC AC current can travel over large distances (from power plant) Transformers convert high voltage to lower voltage

Capacitors Capacitors: devices that store electrical energy by separating charges Can supply power for a short amount of time Measured in farads (F) 1 F = 1 coulomb of charge stored using 1 V

Capacitors Capacitance depends on 3 things Surface area of plates Type of insulator Distance between the plates Smaller distance = greater capacitance Capacitors discharge over time

Capacitors Defibrillators Subwoofers Crosswalk lights