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# The Physics of Hair Dryers

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## Katie Moon

on 1 June 2015

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#### Transcript of The Physics of Hair Dryers

Currents
Switch turns dryer on/off & controls the heat & strength of air.
To control heat: change the power
To control strength: alter the current flowing through the part of the circuit feeding the motor
Best hair dryers have between 1300-1875 Watts
Current Cont.
Current flows from outlet to hair dryer
Goes through heating coils
big resistance=big voltage drop
AC current converted to DC current
Electric motor spins fan
Fan pushes air out of barrel over heating coils

Energy
How Hair Dryers Work
Need power source (outlet)
Turn on the hair dryer
Electricity powers the heating element & fan
Fan blows air over heating element
Air is heated
The Physics of Hair Dryers
Electrical potential energy is converted to thermal energy

Thermodynamics: study of heat transformations into other forms of energy
net heat transfer = change in internal energy + work
Q = U + W

q = m C (Tf - Ti)
What is a hair dryer
A hair dryer is used to accelerate the drying process of wet hair.
History
Invented by Alexander Godefroy in France in 1890
Energy Cont.
Electrical potential energy
U=(kQq)/r

Electric potential
V=Work/unit of charge moved
=U/q

Parts of a Hair Dryer
Outlet/Plug
Ground-fault circuit interrupter senses difference in power between the 2 prongs & shuts down power flowing through dryer when there's a short (current is being drawn at too high a rate)
Large prong (neutral)
Small prong (hot)
Polarized plug because it matters which way it's plugged in

Power wants to be grounded
Switch
Controls electricity going into dryer
Different settings
Ex: Conair 1875
16 A at 125 V
8 A at 250 V
Heating Element
Resistor & doesn't oxidize under heat
Warm air holds more moisture than cold
Thermal fuse - cuts off power if temperature goes too high
Bimetallic strip - has 2 different metal alloys expand at different rates, so one pushes in one directions & disconnects electricity
Serves as a giant resistor b/c the motor doesn't need as much voltage as the coils
Ex: Conair 1875
Knocks down voltage from 120 V to 12 V
Bridge Rectifier
Between heating element & motor
Convert AC current to DC current
4 diodes convert the sine waves of AC currents to DC currents b/c the motor needs a continuous loop of electricity
Electric Motor/Fan
Powered with DC current
Pulls air in & directs it around heating element
Ohm's Law
I= V/R
Current is directly proportional to electrical potential difference & inversely proportional to total resistance
Increase/decrease resistance in branch of circuit=Decrease/increase current in circuit
P=VI=I^2R=V^2R
Change one and all the rest change

Voltage:
electrical potential difference
electric potential
potential difference.

Electric potential energy per unit charge
Full transcript