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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
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
...1111
321
RRRRP
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 V1 Ω 0.25 A 0.25 V2 Ω 0.25 A 0.50 V3 Ω 0.25 A 0.75 VTotal = 6 Ω
Total = 0.25 A
Total = 1.5 V
• 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.
Parallel Circuits
R I V1 Ω 3 A 3 V2 Ω 1.5 A 3 V3 Ω 1 A 3 VTotal = 6/11 Ω
Total = 5.5 A
Total = 3 V
...1111
321
RRRRP
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
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)
Fuses
• A fuse prevents too much current from flowing through a circuit
• It “breaks” if the current is too high.
Additional Problems1. Determine the power used by a hair dryer
that draws a current of 8 amps and runs on 120 volts of electricity.
2. Determine the current used by an iPod that runs on a 3.7 V battery and has a power of 2 watts.
3. Convert 200 cV to kV4. 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. 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– 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