Transcript Dynamic Electricity - RiverdaleCollinsScience

Dynamic Electricity
What is a conductor and insulator?
A conductor is a material which allows an electric
current to pass. Metals are good conductors of
electricity.
An insulator is a material which does not allow an
electric current to pass. Nonmetals are good conductors
of electricity. Plastic, glass, wood, and rubber are good
insulators
What is the difference between static
electricity and current electricity?
Static electricity is stationary or collects on
the surface of an object, whereas
current electricity is the flow of
electrons very rapidly through a
conductor.
Current Intensity
This is how many electrons are flowing through
an electrical circuit every second.
Current Intensity (I) is measured in amperes (A)
1 Amp is equal to 1 C per second.
I = q_
∆t
1C=1A
1s
I is current intensity (A),
q is charge (C), ∆t = seconds
(C stands for Coulomb, the unit of electrical charge)
Question
A car headlight requires a current of 15 A.
How much charge, in Coulombs are
needed to operate the headlight for one
minute?
Answer
I = q/ ∆t, therefore q = I x ∆t
q = 15 x 60 = 900 Coulombs of charge
The flow of electricity in current electricity
has electrical pressure or voltage. Electric
charges flow from an area of high voltage to
an area of low voltage.
Water pressure and voltage behave in similar ways.
Voltage is like
the water
pressure in the
upper reservoir
pushing the
water through
the pipe. The
difference in
pressure is
called Potential
Difference.
The unit used to measure voltage is volts (V).
Voltage is calculated as the energy (joules)
pushing each coulomb (C) of charge through the
circuit.
V=E
q
V = voltage (V), E = energy (J)
q = charge (C)
Question: How much energy is transferred by
200 C of charge in a home with 110 V voltage?
Answer
V = E/q therefore E = V x q
E = 110 x 200 = 22 000 joules of energy
(Also, 22 kJ would be correct)
What are batteries?
Batteries are composed of a chemical substance which
can generate voltage which can be used in a circuit.
There are two kinds of batteries: dry cell and wet cell
batteries. Below is an example of a dry cell.
The zinc container of the
dry cell
contains a moist chemical
paste surrounding a carbon
rod suspended in the
middle.
Wet cell batteries are most commonly
associated with automobile batteries.
A wet cell contains two
connected plates made of
different metals or metal
compounds in a
conducting solution. Most
car batteries have a series
of six cells, each
containing lead and lead
oxide in a sulfuric acid
solution.
What is electrical resistance?
Resistance (R) is the opposition to the flow of
an electric current, causing the electrical energy
to be converted to thermal energy or light.
The metal which makes up a
light bulb filament or stovetop
eye has a high electrical
resistance. This causes light
and heat to be given off.
The unit for measuring resistance is the
ohm (Ω).
Also , colder wires have less resistance than hot wires.
Electrical Calculations – What is Ohm’s Law?
I=
3V
2Ω
I = 1.5 amps
Power
• Electrical power is the amount of energy
used by an electrical device every second.
• This energy can be used to perform work.
• P=E
∆t
power is measured in watts (W)
energy is measured in joules (J)
Question
• An ipod device uses 12 watts of power. If it
is run for 10 hours, how much energy is
used?
Answer
• Power = energy/time
therefore
energy = power x time
= 12 watts x 10 hours x 60 min x 60 sec
= 432 000 joules
Another way to calculate power
• Power can also be calculated using
Voltage and Intensity.
P = V•I
Ex.
if a television uses 110 watts at home
and voltage is 110 V, How much
current does it need?
Answer
P=
V•I
therefore I = P
V
I = 110 W = 1 amp
110 V
And…
• For really big quantities of energy we use
kilowatts of power and hours of time.
• 1 kW•h = 1000 watts x 3600 seconds
= 3600 000 joules.
We pay for electricity by the kW•h, so it’s handy
to know this calculation.
E = P X time
P=IV
Example problem:
Answer
P = (2A) (120 V) = 240 W = .240 kW
E = (.240 kW) (4 h) = 960Wh = 0.96 kWh
(We pay about 7 cents per kWh of electricity
in Quebec)
How is Electrical Power calculated?
Electrical Power is the product of the current (I) and the
voltage (v)
The unit for electrical power is the same as that for
mechanical power in the previous module – the watt (W)
Example Problem: How much power is used in a circuit
which is 110 volts and has a current of 1.36 amps?
P=IV
Power = (1.36 amps) (110 V) = 150 W