Transcript Electromagnetic wave

Electromagnetic
Waves
Electromagnetic
wave
Ultraviolet
radiation
Radio wave
X-rays
Infrared wave
Gamma rays
Visible light
What are electromagnetic
waves?
• Energy travels from the Sun to Earth as
electromagnetic waves.
• Electromagnetic wave is a wave that
can travel through matter or space.
What are electromagnetic
waves? (cont.)
• If a charged particle moves up and
down, its electric field also moves up and
down.
• The changing electric field produces a
changing magnetic field.
• A wave of vibrating electric and magnetic
fields moves outward in all directions.
What are electromagnetic
waves? (cont.)
What are electromagnetic
waves? (cont.)
• All matter produces electromagnetic waves.
• There are many different types of
electromagnetic waves.
– These waves have a wide range of wavelengths,
frequencies and energy they contain.
– As wavelength shortens and frequency increases,
the energy of the electromagnetic wave increases.
What are electromagnetic
waves? (cont.)
• The range of electromagnetic waves forms the
electromagnetic spectrum.
• The spectrum is arranged from long waves
with the lowest amount of energy to short
waves with the highest amount of energy.
What are radio waves and
infrared waves?
• Radio waves the lowest-frequency
electromagnetic waves that have wavelengths
greater than about 0.3m and are used in most
forms of communication technology – such as
TVs, telephones and radios.
What are radio waves and
infrared waves? (cont.)
What are radio waves and
infrared waves? (cont.)
• Microwaves are radio waves between 0.3m
and 0.001m.
– Ex. Radar, Doppler, police and air-traffic control,
global positioning systems (GPS), communication,
cell phones and cooking food
What are radio waves and
infrared waves? (cont.)
• Infrared waves electromagnetic waves with
wavelengths between 1mm and 0.7millionths of
a meter.
• Electrons in atoms and molecules are vibrating
and emitting electromagnetic waves.
What are radio waves and
infrared waves? (cont.)
• Most of the electromagnetic waves given off
by objects at room temperature is infrared –
heat.
– Ex. Night vision goggles, thermal cameras
Why do we see color?
• Visible light a mixture of wavelengths
that the human eye can detect.
• Visible light from the Sun comes to Earth
as white light.
• White light contains a mixture of
wavelengths.
Why do we see color? (cont.)
• When visible light wavelengths are separated,
we see them as different colors.
• This happens when sunlight is refracted
through raindrops – you know it as a rainbow.
– Prisms and a diffraction grating can also separate
visible light into its separate wavelengths.
Why do we see color? (cont.)
• When visible light is refracted, the separate
colors are always in the same order from longest
wavelength to shortest wavelength.
– ROY G. BIV – red, orange, yellow, green, blue,
indigo and violet.
• Red light has the longest wavelength and the
lowest frequency.
• Violet light has the shortest wavelength and the
highest frequency.
Why do we see color? (cont.)
• Most objects you see do not give off visible
light. They simply reflect, refract and/or
absorb the visible light that is emitted by a
source of light, the Sun or a lightbulb.
– Ex. A red shirt appears red because it reflects red
light and absorbs all the other colors.
– Your whiteboard appears white because it reflects
all the colors.
– Why are tires black?
• They absorb all visible light
What are ultraviolet rays and xrays?
• Ultraviolet radiation electromagnetic waves
with wavelengths between about 0.4millionths
of a meter and 10billionths of a meter; has
frequencies and wavelengths between visible
light and x-rays.
What are ultraviolet rays and xrays?
• Ultraviolet waves
– carry enough energy to move through clouds and to
penetrate skin, which can cause sunburn or even
skin cancer.
– enables your body to produce the Vitamin D (with
small amounts of exposure to the Sun)
– Kills viruses and bacteria by destroying their DNA.
Ultraviolet lamps are used in operating rooms and
for sterilizing medical equipment.
What are ultraviolet rays and xrays? (cont.)
• X-rays high-energy electromagnetic waves
that can be used for medical diagnosis.
– Destroy living cells
– Penetrate deeper into the body than UV and can
damage muscles and organs.
– One medical X-ray is not harmful but numerous Xrays can be dangerous.
What are ultraviolet rays and xrays? (cont.)
• The ozone layer in Earth’s atmosphere serves
as a shield to block some types of
electromagnetic waves from reaching Earth’s
surface.
– Radio waves and Visible light move easily
through Earth’s atmosphere.
– Infrared waves and Ultraviolet waves are partially
blocked.
– X-rays and gamma rays are completely blocked
What are gamma rays?
• Gamma rays the highest-energy
electromagnetic waves with the shortest
wavelengths and highest frequencies.
– Have enough energy they can pass through several
centimeters of lead.
– Have enough energy that physicians can use them
to destroy cancerous cells.
– Although blocked by Earth’s atmosphere, gamma
radiation is found on Earth due to radioactive decay
of certain elements.
Which has a wavelength longer
than about 30 cm and is used for
communication?
A. X-ray
B. Radio wave
C. Microwave
D. Gamma ray
Which are produced when the
nucleus of an atom breaks apart
or changes?
A. X-ray
B. Ultraviolet ray
C. Infrared wave
D. Gamma ray
What do vibrating molecules in
any matter emit?
A. X-rays
B. Radio waves
C. Infrared waves
D. Gamma rays
Heat
Essential Question
• How is thermal energy
transferred?
Heat
Heat
Radiation
Conduction
Specific heat
Convection
What is heat?
• Heat the flow of thermal energy from
warmer to cooler objects.
• As an object is heated, the total amount
of kinetic energy, or thermal energy,
within the object increases.
• Thermal energy always flows from a
higher-temperature material to a lowertemperature material.
What is heat? (cont.)
• As thermal energy flows into a substance,
kinetic energy increases causing an increase
in temperature.
• This increase in energy can also cause
particles to move farther apart causing an
increase in volume known as thermal
expansion.
– Ex. Thermometers
• The total amount of thermal energy in a
substance depends on a combination of
temperature and mass.
How does heat travel?
• Thermal energy is transferred in three
ways.
– By conduction
– By convection
– By radiation
How does heat travel? (cont.)
• Conduction the movement of energy, such as
heat or electricity, through direct contact.
– Occurs in solids, liquids and gases.
• Ex. Cool drink warming in the air.
– The hot air transfers thermal
energy to the cool lemonade by
conduction. (direct contact)
– Eventually the kinetic thermal
energy and temperature of the air
and the lemonade will be equal.
How does heat travel? (cont.)
• Convection the
transfer of energy by
the flow of a liquid or a
gas.
– Caused by hot parts
rising and cool parts
sinking because most
liquids and gases
become less dense
when heated.
• Ex. Heating water.
How does heat travel? (cont.)
Convection Currents in Earth’s Atmosphere
How does heat travel? (cont.)
• Radiation the transfer of thermal energy
through electromagnetic rays.
– No medium is necessary because electromagnetic
rays can travel through empty space.
– Ex. Sun heating Earth, toasters, ovens.
How does heat travel? (cont.)
• When you are cold, you try to trap heat energy
around your body.
– This is why cold weather garments are often dark.
Dark colors absorb more energy.
– Summer clothes are light because they absorb less
energy (reflect more light) and allow heat to flow
away from the body easily.
How do we use heat?
• Buildings are heated by systems designed to
transfer heat energy.
How do we use heat? (cont.)
• Heating systems usually have a thermostat
that turn the system on and off automatically.
– The switch on the thermostat is often a strip made
of two different kinds of metals joined together and
bent into a coil.
– The metal on the inside of the coil expands and
contracts more than the metal on the outside of the
coil.
– When a room warms or cools, the thermal energy
causes the bimetallic coil to uncurl slightly or
tighten, which turns the furnace off or on.
How do we use heat? (cont.)
• Gasoline is burned in a car’s engine and
through thermal expansion causes the
crankshaft to move.
How do we use heat? (cont.)
• Gasoline is burned in a car’s engine and
through thermal expansion causes the
crankshaft to move. (cont.)
What is specific heat?
• Specific heat is the
Specific Heat of Substances
amount of heat energy,
usually measured in
Specific Heat
Substance
(in J/g °C)
joules, needed to raise
the temperature of 1gram Aluminum
0.90
of a substance by 1°C.
• Changing the
temperature of a material
with a low specific heat is
easier than to change the
temperature of a material
with a high specific heat.
Cooper
0.39
Iron
0.45
Mercury
0.14
Water (liquid)
4.19
Which term refers to the average
kinetic energy of the particles that
make up a material?
A. heat
B. temperature
C. potential energy
D. thermal energy
Which describes an increase in
a material’s volume when its
temperature increases?
A. conduction
B. thermal expansion
C. thermal conductor
D. thermal contraction
Which term refers to a device
that regulates the temperature
of a system?
A. heat engine
B. heating appliance
C. refrigerator
D. thermostat
Electricity
Essential Question
• What is electricity and how can it
be produced?
Electricity
Electricity
Series circuit
Static electricity
Parallel circuit
Current
electricity
Generator
Resistor
What is electricity?
• Remember that:
– Protons and neutrons
make up the nucleus
of an atom.
– Protons in the nuclei
of atoms have positive
charge.
– Electrons moving around
a nucleus have negative
charge.
What is electricity?
• As electrons move from one atom to
anther, the charge moves from atom to
atom as well.
• Electricity is a flow of electrons, or
particles that have negative electrical
charges.
• The flow of electricity is energy that is
available for creating change.
What is electricity? (cont.)
• When two materials touch one another,
electrons can move from one material to
the other.
• This causes one material to become
more negatively charged than the other.
– Material that gained the electron becomes
negatively charged.
– Material that lost the electron becomes
positively charged.
What is electricity? (cont.)
• Static electricity is the buildup of an
electric charge, either positive or
negative, on a material’s surface.
• Objects with opposite electric charges
attract each other, and objects with
similar electric charges repel each other.
What is electricity? (cont.)
• Charged objects can attract or repel each
other. The arrows show the direction of
the objects’ motion.
What is electricity? (cont.)
• The strength of the electric force
between two charged objects depends
on the total amount of charge on both
objects and the distance between the
objects.
How can electricity jump?
• A discharge corrects an imbalance, or
difference, in charge through the rapid
movement of electrons.
– Ex. Getting shocked when you touch a
light switch or doorknob.
• Shuffling your feet on the carpet causes
electrons to move from the carpet to you,
making you negatively charged. When you go
to reach for the light switch or doorknob, the
electric charge jumps from you to the switch or
doorknob.
How can electricity jump? (cont.)
• When a charged object is placed near a
neutral object – an object with no net
charge – the charged object can affect
the overall charge of the neutral object.
– An induced charge is a static charge
caused by the presence of an object that
has a net positive or negative charge.
How can electricity jump? (cont.)
• Ex.
– A negatively
charged balloon
repels electrons in
a metal soda can.
– The can is not
charged because
it has not gained
or lost any
electrons.
– When electrons
concentrate at
one end of an
object, the object
is polarized.
How can electricity jump? (cont.)
– When a charged
balloon is brought
near two cans that
are touching, the
balloon polarizes
the cans as if they
are one object.
– Electrons in both
cans move toward
the far end of the
can on the right.
Then, the two
cans separate.
How can electricity jump? (cont.)
– The cans that were
originally polarized
as a group are now
individually
charged.
– The can on the
right has an
unbalanced
negative electric
charge, and the
can on the left has
an unbalanced
positive electric
charge.
How can electricity jump? (cont.)
• One huge electric
discharge that occurs in an
instant is lightning.
–
Air currents cause clouds
to become polarized with
the negative charge at the
bottom of the cloud.
–
The negatively charged
cloud bottom, repels the
electrons on the ground,
inducing a positive charge
in the ground.
–
A lightning flash occurs
when huge amounts of
electrons jump from the
cloud to the ground.
How can electricity jump? (cont.)
• A lightning strike
can severely
damage a
building or injure
people.
Lightning rods
help protect us
against these
dangers.
How can electricity flow?
• The path that electrical energy flows through a
conductor is called a circuit.
– A simple circuit consists of an energy source, such
as a battery, electrical devices, such as a lamp, and
connecting
wires.
– An energy source,
such as a battery,
produces an electric
current in a circuit.
• Current electricity the flow of electrons moving
through a circuit.
How can electricity flow? (cont.)
• All electric circuits have one thing in
common—they transform electric energy
to other forms of energy.
– Ex. Flashlight – chemical energy from the
batteries to electrical energy through the
wiring to light energy through the light bulb.
• The number of electrons flowing into a
wire from a power source equals the
number of electrons flowing out of the
wire back into the source.
How can electricity flow? (cont.)
• An electric current
flows in a circuit if
the circuit is
complete, or
closed.
• Current will not
flow if the circuit is
broken, or open.
How can electricity flow? (cont.)
• Resistor is a material through which
electricity has difficulty flowing.
– Lights and other devices connected in a
circuit act as resistors, because they also
reduce current flow.
How can electricity flow? (cont.)
• The simple circuit in a flashlight uses
direct current, or DC, which refers to
current that flows in one direction.
– Ex. Batteries, solar cells
• Alternating current, or AC, refers to a
current that changes direction, moves
back and forth, at regular intervals.
– Ex. Microwaves, toasters, computers
What are some kinds of circuits?
• There are two types of electric circuits—
series circuits and parallel circuits.
– Series circuit is a circuit with only one
path along which current electricity can
flow. Ex. Flashlights
What are some kinds of circuits? (cont.)
– Parallel circuit is a circuit with multiple
paths along which current electricity can
flow.
• Parallel circuits have more than one path
through which electric current can flow.
• When one bulb burns out, there are other paths
along which electric charge can flow to all other
bulbs. Ex. Christmas lights
What are some kinds of circuits? (cont.)
• A short circuit is a path for current
electricity that has little or no resistance.
– Can reach dangerously high levels and
generate heat.
• In bathrooms and kitchens, outlets have
small buttons that say “test” and “reset”.
These are part of a ground fault
interrupter.
– The GFI will turn an outlet off if a short
circuit forms.
How do we use generators?
• Generator is a device that converts
mechanical energy – supplied by a
hand crank, a turbine, or a motor –
into electricity.
What are some tips on using
Electricity Safety Tips
electricity?
• A fuse is a wire
that breaks if too
much current flows
through it.
• A breaker is a
switch that opens
when it detects too
much current.
• Never touch a wall socket or the metal
part of a plug when you plug
something in.
• Never use a plug that is torn or
damaged; it can cause a short circuit.
• Never pull out a plug by the cord; it
can damage the cord.
• Do not overload an outlet with too
many plugs; this could overload the
circuit.
• Stay away from high-voltage wires. If
you see a downed power line, report it
to your power company.
• Never use electric devices when you
are wet or standing in water.
Which term refers to an electric
circuit with more than one path,
or branch, for electric current to
follow?
A. electrical device
B. fuse
C. parallel circuit
D. series circuit
Which is a source of energy for
an electric circuit?
A. battery
B. lightbulb
C. switch
D. wires
Which two particles attract each
other?
A. two electrons
B. two protons
C. one proton and one neutron
D. one proton and one electron
Visual Summary
Chapter Review
Standardized Test Practice
Energy is the ability to
cause change. Forms of
energy include light, heat,
sound, electrical, nuclear,
and mechanical energy.
Any form of energy can be
transformed into another
form.
Lesson 1: The Nature of Energy
• An object that is moving has kinetic
energy. Potential energy is stored
energy.
Lesson 2: Waves and Sound
• Characteristics of waves include
wavelength, frequency, and
amplitude.
• Vibrating objects produce sound
waves.
Lesson 3: Properties of Light
• Light travels from its source in straight
lines that move out in all direction.
• Matter can absorb, reflect or transmit
light.
Lesson 4: Electromagnetic
Waves
• Electromagnetic waves differ in their
wavelength, frequency and energy.
• An object’s color is determined by the
wavelength of light that object reflects.
Lesson 5: Heat
• Heat is the flow of thermal energy from
warmer to cooler objects.
• Thermal energy is transferred in three
ways – conduction, convection and
radiation.
Lesson 6: Electricity
• A generator is a device that converts
mechanical energy into electricity.
Which term describes the ability
to cause change?
A. energy
B. friction
C. motion
D. work
Which describes the maximum
distance the particles in a medium
move from their rest position as the
wave passes?
A. a wave’s wavelength
B. a wave’s speed
C. a wave’s frequency
D. a wave’s amplitude
Which refers to a material
through which light does not
pass?
A. luminous
B. opaque
C. translucent
D. transparent
Which has a shorter wavelength
and higher frequency than all
other types of electromagnetic
waves?
A. gamma rays
B. radio wave
C. ultraviolet wave
D. x-rays
The transfer of thermal energy
from one material to another by
electromagnetic waves is called
what?
A. conduction
B. radiation
C. specific heat
D. thermal expansion
Which is the distance between
a point on one wave and the
nearest point just like it?
A. amplitude
B. frequency
C. pitch
D. wavelength
Which term refers to what
happens when waves bounce off
a surface of a material?
A. absorption
B. reflection
C. refraction
D. transmission
Which is true according to the law
of conservation of energy?
A. Energy can be created or destroyed.
B. Energy can be created, but not
destroyed.
C. Energy cannot be created or
destroyed.
D. Energy cannot be created but can be
destroyed.
Which uses a mirror to gather and
focus light from distant objects?
A. laser
B. microscope
C. reflecting telescope
D. refracting telescope
In an electric circuit, which
transforms most of the electric
energy to other useful forms of
energy?
A. battery
B. circuit breaker
C. electrical device
D. fuse