Transcript Electricity did not become an integral Part of our daily lives until

Electricity did not become an integral
Part of our daily lives until
Scientists learned to control the
Movement of electric charge.
This is known as current
Electric currents are responsible
For many things; computers,
Cars, and every move you make.
Current is the rate at which
Electric charges move through
A given area.
Conventional current is defined
In terms of positive movement.
Electricity is the movement of
Electrons, the negative charge,
Moving in a direction. This direction
Is 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 energy
And generators use mechanical
Energy.
Current can be direct or alternating.
In Direct Current (DC) the charge
Moves 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.
Q
I=
t
I = electric current
Q = charge through a given area
t = time
The SI unit for current is the
Ampere (A).
The SI unit for charge is the
Coulomb (C).
So the Ampere is 1 C per second.
The amount of charge that passes
Through the filament of a
Certain light bulb in 2 s if
1.67 C. Determine the current in
The 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 conductor
Is the conductor’s resistance.
Resistance is the ratio of the
Potential difference across
A conductor to the current
It carries.
V
R=
I
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 applied
Potential differences.
It is usually shown by…
V = IR
Resistance depends on length,
Cross-sectional area, material,
And temperature.
Resistors can be used to control
The 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 across
A 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. Calculate
The 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 the
Currents in its branches.
A series circuit is one in which
Current passes through one
Device and then another.
Electric companies measure
Energy consumption in
Kilowatt-hours.
1 kW h = 3.6 X 106 J
Electrical energy is transferred at
High potential differences to
Minimize loss. (up to 1000000 V)
When the wires are strung, they are
Very tight and straight, they bow
Because they are soooo hot!
How much does it cost to operate
A 100 W light bulb for 24 hours
If 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 resistor
Causes 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, and
The formula for power, we have
3 new formulas that we can use…
P=
I2R
V2
P=
R
And for the thermal
Energy dissipated…
V2
E=
t
R
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 heater
In 10 s?
1.44 kW
14.4 kJ