Transcript Electricity & Magnetism

Electricity
Currents, Circuits
Electricity that moves…
 Current:
The flow of electrons
from one place to another.
 Measured in amperes (amps)
 Kinetic energy
How can we control currents?
 With
circuits.
 Circuit: is a path for the flow of
electrons. We use wires.
There are 2 types of currents:
Current (DC) – Where
electrons flow in the same
direction in a wire.
 Direct
There are 2 types of currents:
Current (AC) –
electrons flow in different
directions in a wire
 Alternating
There are 2 types of circuits:
 Series
Circuit: the components
are lined up along one path. If
the circuit is broken, all
components turn off.
Series Circuit
There are 2 types of circuits:
Circuit – there are several
branching paths to the
components. If the circuit is
broken at any one branch, only
the components on that branch
will turn off.
 Parallel
Parallel Circuit
What is Resistance?
 The
opposition to the flow of an
electric current, producing heat.
 The greater the resistance, the
less current gets through.
 Good conductors have low
resistance.
 Measured in ohms.
What Influences Resistance?
of wire – aluminum and
copper have low resistance
 Thickness – the thicker the wire the
lower the resistance
 Length – shorter wire has lower
resistance
 Temperature – lower temperature has
lower resistance
 Material
What is Voltage?
 The
measure of energy given to
the charge flowing in a circuit.
 The greater the voltage, the
greater the force or “pressure”
that drives the charge through the
circuit.
Difference b/t Volts and Amps
 Example
 Amps
– you could say that…
measure how much water
comes out of a hose.
 Volts measure how hard the water
comes out of a hose.
Ohm’s Law
 Resistance
 Ohms
= Voltage / Current
= Volts / Amps
Practice with Ohm’s Law
Ohms
4
15
2
9
6
Volts
100
150
30
45
48
Amps
25
10
15
5
8
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.
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
How is electrical energy determined?
Electrical energy is a measure of the amount of power
used and the time of use.
Electrical energy is the product of the power and the
time.
Example problem:
E = P X time
P=IV
P = (2A) (120 V) = 240 W
E = (240 W) (4 h) = 960Wh = 0.96 kWh