electricity did not become an integral part of our daily lives until scientists learned to control...
TRANSCRIPT
Electricity did not become an integralPart of our daily lives until
Scientists learned to control the Movement of electric charge.
This is known as current
Current is the rate at whichElectric charges move through
A given area.
Electric currents are responsibleFor many things; computers,
Cars, and every move you make.
Conventional current is definedIn terms of positive movement.
Electricity is the movement of Electrons, the negative charge,
Moving in a direction. This directionIs in the positive direction.
Solutions that have dissolved Ions can be charge carriers,
These are called electrolytes.
Drift velocity is the net velocity of a charge carrier moving in
An electric field.
Drift speeds are relatively small.
The speed of an electron in a Copper wire is only about
0.000246 m/s! The electric Field, on the other hand, is Almost the speed of light.
Batteries and generators Supply energy to charge carriers.
Both batteries and generators Contain a potential difference (volts) across their terminals.
Batteries use chemical energyAnd generators use mechanical
Energy.
Current can be direct or alternating.
In Direct Current (DC) the chargeMoves only one way through the
Wire. (like my electric truck)
In Alternating Current (AC), the Charges are constantly changing,
Creating no real movement of Electrons.
Our house current in the US is 60 Hz.
I = Qt
I = electric currentQ = charge through a given area
t = time
The SI unit for current is the Ampere (A).
The SI unit for charge is theCoulomb (C).
So the Ampere is 1 C per second.
The amount of charge that passesThrough the filament of a Certain light bulb in 2 s if
1.67 C. Determine the current inThe light bulb.
I = 0.835 A
There are insulators and Conductors, but there are also
Not so good conductors. The impedance of the motion of
Charge through a conductorIs the conductor’s resistance.
Resistance is the ratio of the Potential difference acrossA conductor to the current
It carries.
R = VI
SI unit for resistance is the Ohm,And is represented by Ω.
Ohm’s law states that the Resistance is constant over a
Wide range of appliedPotential differences.
It is usually shown by…
V = IR
Resistance depends on length,Cross-sectional area, material,
And temperature.
Resistors can be used to controlThe amount of current
In a conductor.
The plate on an iron states that The current in the iron is 6.4 A
When the iron is connected acrossA potential difference of 120V.
What is the resistance of the iron?
R = 19 Ω
Electric power is the rate of Conversion of electrical energy.
P = IV
The SI unit is the Watt.
An electric space heater is Connected to a 120 V outlet. The Heater dissipates 3.5 kW of power
In the form of heat. CalculateThe resistance of the heater.
R = 4.1 Ω
An electric circuit is a Continuous path through which
Electric charges can flow.
There are two types of circuit Connections,
Parallel & Series
A parallel circuit is one with Several current paths, whose
Total current equals the sum of theCurrents in its branches.
A series circuit is one in whichCurrent passes through oneDevice and then another.
Electric companies measureEnergy consumption in
Kilowatt-hours.
1 kW h = 3.6 X 106 J
Electrical energy is transferred atHigh potential differences to
Minimize loss. (up to 1000000 V)
When the wires are strung, they areVery tight and straight, they bow
Because they are soooo hot!
How much does it cost to operateA 100 W light bulb for 24 hoursIf electrical energy costs $0.08 Per kW h? What is the cost per
Year? What is the cost if you used A energy conserving bulb at 14 W?
Cost = $0.19/day $69/year
Cost = $ 0.03/day$9.81/year
Current moving through a resistorCauses it to heat up because
Flowing electrons bump into the Atoms in the resistor.
These collisions increase the Atoms’ kinetic energy and, thus, The temperature of the resistor.
If we rearrange Ohm’s Law, andThe formula for power, we have
3 new formulas that we can use…
P = I2R
P = V2
R
And for the thermalEnergy dissipated…
E = V2
Rt
A heater has a resistance of 10 Ω. It operates on 120 V.
What is the power dissipated by The heater? What is the thermal
Energy supplied by the heaterIn 10 s?
1.44 kW 14.4 kJ
