Transcript Electricity

ELECTRICITY
CHAPTER 1
ELECTRIC CHARGE
• Charges Exert Force
• Atoms are composed of particles with ______. The law
of electric charges states that like charges _____and
opposite charges _______
THE FORCE BETWEEN PROTONS AND
ELECTRONS
• Protons and electrons have ________ charges, they
are ________ to each other
THE ELECTRIC FORCE AND THE
ELECTRIC FIELD
• _____________ the force of attraction or repulsion on
a charged particle that is due to an electric field
• ____________ – the space around a charged object
in which another charged object experiences an
electric force
CHARGE IT!
Friction
• ________- occurs when
electrons are “wiped”
from one object to
another
Conduction
• __________ – electrons
move from one object to
another by direct
contact.
CHARGE IT!
• _________ – charges in an uncharged metal object
are rearranged without direct contact with a
charged object
CONSERVATION OF CHARGE
• When you charge something by any method,
____________________________________. The numbers
of ________ and _______ stay the same.
• Detecting Charge
• You can use a device called an _____________ to
see if something is charged
MOVING CHARGES
• __________- a material in which charges can move
easily
• Examples:
• __________- a material in which charges
cannot move freely
• Examples:
STATIC ELECTRICITY
• _________________ electric charge at rest; produced
from friction or induction
• _________________ – the release of electricity stored
in a source
1.2 ELECTRIC CURRENT & ENERGY
• _______________ – rate at which charges pass a
given point
• When you flip a switch, an _____________ is set up
in the wire at the speed of light. The electric field
causes the _________ in the wire to move.
• This electric field is created so quickly that all
electrons start moving through the wire _________.
• Think of the electric field as a command to the
electrons to charge ahead.
TYPES ELECTRIC CURRENT
Direct Current (DC)
• ___________________ –
charges always flow in
one direction.
• Ex:
Alternating Current (Ac)
• ___________________ –
charges shift
from flowing in one
direction to flowing in
the reverse direction
• EX:
VOLTAGE AND ENERGY
• _______ – the potential difference between points
• SI unit :
• You can think of voltage as the amount of energy released as
a charge moves between two points in the path of a current.
• As long as there is a voltage between _________, charges
will flow in the wire. The ____ of the current depends on the
_______
Varying Nature of Voltage
• Different devices need different levels of voltage.
1.5 V
9V
12 V
Resistance
• ___________ – opposition to the flow of electric
charge
• SI unit:
• Good conductors, such as copper, have _____________
• Poor conductors, such as iron, have ______________
• Resistance depends on thickness, length, &
temperature
• Thick, _____ wires have ____ resistance than ____, thin wires.
• The resistance of metals _________ as temperature _________
Resistance
Generating Electrical Energy
• Remember energy is not created or destroyed – it
only changes forms
• Parts of a Cell
• A cell contains a mixture of chemicals called an __________.
Every cell also has a pair of __________made from
conducting materials
Types of Cells
• There are 2 types of cells:
• ___ – have an electrolyte
• Example: batteries – sulfuric acid is the electrolyte
• ___ – have a dry electrolyte
• Example: small radios or flashlights
Generating Electrical Energy
• Cells change chemical or radiant energy into
electrical energy. Batteries are made of one or
more cells.
• ____________ can take thermal energy and transfer
it to electrical energy.
• _________convert light energy into electrical energy.
1.3 ELECTRICAL CALCULATIONS
• How fast is a nanosecond? A nanosecond (ns) is
one-billionth of a second. Electrical signals travel at
30 cm/ns. Calculate how far electrical signals travel
in 1 second.
•
CONNECTING CURRENT, VOLTAGE,
AND RESISTANCE
• Georg Ohm Ohm (1789 –1854) studied the
resistance of materials. He measured the current
that resulted from different voltages applied to a
piece of metal wire.
Electric Power
• Ohm’s Law – the ratio or voltage (V) to current (I) is
the resistance (R) of a material
• V=IxR
Unit
SI Unit
Voltage (V)
V - volt
Current (I)
A- Amps
Resistance
(R)
Ohm - Ω
OHM’S LAW CALCULATIONS
• Ex: 1 What is the voltage if the current is 2 A and the
resistance is 12 Ω ?
• Ex: 2 Find the voltage if the current is 0.2 A and the
resistance is 2 Ω
OHM’S LAW CALCULATIONS
• Ex 3: The resistance of an object is 4 Ω. If the current
in the object is 9 A, what is the voltage used?
• Ex 4: An object has a resistance of 20 Ω. Calculate
the voltage needed to produce a current of 0.5 A.
ELECTRIC POWER
• Electrical Power (P) – the rate at which electrical
energy is converted into other forms of energy
• Si Unit: Watts (W)
• Power = voltage x current
• P=VxI
Unit
SI Unit
Voltage (V)
V - volt
Current (I)
A- Amps
Power (P)
W - Watts
ELECTRICAL POWER CALCULATIONS
• Ex 1: A toaster draws approximately 10 A of current.
A home receives 120 V at each electrical outlet.
What is the power of the toaster?
• Ex 2: A car uses a 12 V battery. One headlight draws
3.0 A. What is the power of the headlight?
ELECTRICAL POWER CALCULATIONS
• EX 3: A light bulb draws a 0.5 A current at a voltage
of 120 V. What is the power rating of the light bulb?
ELECTRICAL ENERGY
• Measuring Household Energy Use
• Different amounts of electrical energy are used
each day in a home. Electric companies usually
calculate electrical energy by multiplying the
power in kilowatts by the time in hours.
1.4 ELECTRIC CIRCUIT
• Just like a roller coaster, an electric circuit always forms a
loop— it _____ and ____ at the ____ place
• Parts of an Electric Circuit
•
•
•
(light bulb, appliance)
SWITCHES
• Sometimes, a circuit also contains a _____
• _____ – opens or closes a circuit
• _____ – electrons can ____
• _____ – electrons _____________
TYPES OF CIRCUITS
• ______________– a circuit in which the parts are joined
one after another such that the current in each part is
the same.
• _________for charges to follow – charges must flow through
each part of the circuit
• The voltage across each load is _________
Series circuits are useful
in wiring burglar alarms. If
any part of the
circuit fails, there will be
__________in the system
and the alarm will sound.
TYPES OF CIRCUITS
• _______________- a circuit in which the parts are
joined in branches so that the voltage (potential
difference) across each part is the same
• Loads do ___have the _________________
• Charges have more than ___ path to follow
Parallel Circuits are used
in almost all appliances
and decorative string
lights
HOUSEHOLD CIRCUIT SAFETY
• Circuits can ____ if they are __________ or a wire
breaks or has water damage.
• To prevent fire:
•
• A thin strip of metal in circuit that the charges flow through.
If the current is too high, the metal will melt and the circuit
is broken
•
• A switch that automatically opens if the current is too high. A metal
strip heats up, bends, and opens the switch stopping the flow of
current