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Sound
S U B T ITLE
What is Sound?
• Sound is produced when something vibrates, which means
it moves back and forth very quickly
• When something vibrates, it passes the vibration into its
surrounding environment
• The vibration creates regions of space in which the air
particles are bunched together, called compressions and
regions in which they spread out called rarefactions
• A sound wave is the movement of alternating compressions
and rarefactions
Types of Waves
• Transverse wave a wave in which the vibration is at
right angles to the direction the wave is travelling
• Longitudinal wave a wave in which the vibration is
in the same direction that the wave is travelling
The Speed of Sound
• The more closely packed particles are packed
together, the faster a sound wave will travel through
it
• As a result, sound travels faster through solids than
through liquids, and faster through liquids than
gases
Where does Sound Go?
• Sound passes through thin walls and is transmitted short
distances through most materials
• Hard surfaces such as concrete or bathroom tiles, reflect sound
waves
• This reflected sound is known as an echo
• The time difference between sending and receiving sound can
be measured e.g. calculating the depth of objects in the sea
using sonar
• Soft materials like curtains, carpet and cushions absorb sound
and convert it to heat
• Sound absorption like this is needed in concert halls, so there is
no overlap between sounds performed and their echoes which
would other wise distort what you hear
Frequency and Pitch
• Frequency the number of waves passing a point every
second
• Hertz the unit to measure frequency
• Wavelength the distance from one peak of a wave to the
next, measured in metres
• Louder sounds have larger peaks so louder sounds have
greater sounds than softer sounds
• Pitch is the highness or lowness of sound. The pitch that
you hear depends on the frequency of the vibrating air
• Our ability to hear higher frequencies of sound reduces as
we age
• Young people hear a range of frequencies up to 20 000 Hz, yet most
people over 65 years cannot hear frequencies above 5000 Hz
• Ultrasound is the name given to sound waves with
frequencies above our hearing range e.g. ultrasound in
pregnancy
• Infrasound is the rang of sound below our frequencies
The Ear: How you hear
• Your ears collect sound waves, amplify their vibrations and convert
these into electrical impulses
• Your brain interprets these impulses as sound
• The measurement for sound is the decibel dB
• The sound level above 130 dB can cause pain
• Exposed to sound levels of 80 dB long enough can also cause
damage to your ears
• The threshold of hearing is the smallest sound level that can be heard
when the air is vibrating at 1000 Hz
The Electromagnetic Spectrum
• Electromagnetic spectrum complete range of wavelengths
of energy radiated as electric and magnetic fields
• Radio waves include the low-energy waves that are used to
communicate over long distances through radio and
television, they also include radar and microwaves
• Infra-red radiation invisible to the human eye is emitted by
all objects and is sensed as heat. The amount of infrared
radiation emitted by an object increases as its temperature
increases
• Visible light is necessary for the sense of sight and
photosynthesis
• Ultraviolet radiation is invisible to the human eye, it helps
the body produce vitamin D, too much causes sunburn
• X-rays have enough energy to pass through human flesh;
can be used to kill cancer cells, find weakness in metals.
Bones absorb more x-ray energy than sorter tissue
• Gamma rays have more energy than x-rays and also do
more damage to living cells
• Electromagnetic waves transmit energy from one place to
another
Light
Properties of Light
Light hits the surface and
The material is called
Examples
Almost all light is transmitted
through the substance. A
clear image can be seen
through it.
Transparent
Clear glass
Shallow water
Some light may be reflected,
and light that passes through
is scattered. An image seen
through it is fuzzy.
Translucent
Tissue paper
Fingernails
Frosted glass
Light is either reflected from
or absorbed into the
substance, and no light is
transmitted. No image can be
seen through it.
Opaque
A brick
A piece of wood
A desk
A football
The Law of Reflection
• According to the law of reflection:
angle of incidence = angle of
reflection
Refraction
• Refraction is the bending of light as it enters or leaves different
substances
• Light refracts when it travels from one transparent substance into
another
Convex Lenses
• A lens is a transparent piece of plastic or glass that is shaped or
curved outward or inwards
• A lens that bulges outwards is called a convex lens
• It enlarges the virtual image like a magnifying glass
Concave Lens
• A lens that curves inwards is called a concave lens
• A concave lens only produces images that are smaller upright and
virtual
The Eye
• Light enters the eye, is refracted by the cornea and
focused by the lens which is convex
• The clear upside-down image is formed on the
retina at the back of the eye
• This image is converted into a series of electrical
signals, which then travel along the optic nerve to
the brain for the brain to interpret the information
Vision Problems
• Short-sightedness (myopia) can focus on close
objects, such as a book, but distant objects such as
children in a playground are not clear
• Long-sightedness (hyperopia) can see distant
objects clearly but has trouble focusing on close
objects. They need to use glasses for reading or
doing close work
The Visible Spectrum
• Visible spectrum is the range of colours that can be seen by the eye
• Dispersion splitting of white light into separate colours.
• We see a red apple as being red if it reflects red light towards our
eyes; it will absorb yellow green, blue, indigo and violet
• The seven colours are: red, orange, yellow, green, blue, indigo, violet
• Primary colours: red, green and blue
• Secondary colours: magenta, cyan and yellow
• Your eyes have three types of photoreceptor cells called cones. Each
type of cone is sensitive to one of the primary colours.
• Combinations of signals from these three types of cells can give us
our full colour view of the world
Heat and Electricity
Heat
Conduction
• Conduction is the transfer of heat through a substance as a
result of neighbouring vibrating particles
• By colliding with other particles they transfer some of
their energy to other particles
• Most solids are better conductors than liquids and gases
because their particles are closer together
• Materials that are poor conductors are called insulators
Convection
• Convection is the transfer of heat through the flow of
particles
• Convection current is circular movement that occurs when
warmer, less dense fluid particles rise and cooler, denser
fluid particles sink
Radiation
• Heat is transferred without the presence of particles as
electromagnetic radiation
Electricity
• Static electricity is the build up of charge on the surface
• Electrons have rubbed off of one surface and have transferred it
to another surface
• If a build up of charge continues, electrons may jump across the
gap from the negatively charged surface to the positively charged
surface
• As they jump back, the electrons release all their energy in one go
into heat, light, sound and motion like a lightening bolt
• Current is the moment of charge
• These moving electrons have energy that is transformed into
other forms of energy as the electrons pass through thrings like
globes, heating elements and motors
Simple Electric Circuits
• Electrons need a path to travel around so they can deliver their
energy called an electric circuit
• An electrical circuit needs 3 things
1. An energy source e.g. Battery (power supply)
2. An energy war e.g. light globe, motor (load)
3. Wires to connect everything (conducting path)
Current and Voltage
• Current is a measure of how much electric charge flows
through a circuit, the more charge that flows, the bigger
the current
• Current is measured in units called amps, the symbol is A
• Voltage is the measure of the difference in electrical energy
between two parts of a circuit, the bigger the difference in
energy, the bigger the voltage
• Voltage is measure in units called volts, the symbol is V
Series and Parallel Circuits
• In a series circuit all the components of the circuit are connected up
one after another to form a single loop
• In this type of circuit there is only one path for the current to flow
• A parallel circuit has a number of branches where each branch has its
own components
• Each bulb glows as brightly as if it was the only bulb in the circuit
• If you disconnect on bulb the other still glows, because the current
still flows through the unbroken branch of the circuit
Using an Ammeter
• An ammeter is used to measure the size of electric
current flowing in an electric circuit
• It measures the electric current in amperes
• It is connected in series with the circuit
Using a Voltmeter
• A voltmeter is used to measure the voltage gain
across the terminals of a power supply or voltage
drop across parts of an electric circuit
• It is measured in volts
• It is connected in parallel to the circuit
Resistance
• How much current flows in a circuit is determined by the resistance of
the circuit
• The electrical resistance of a material is a measure of how difficult it is
for charged particles to move through it
• Most connecting wires have very low resistance and hardly any
energy lost by the electrons
• Resistors are devices that are placed deliberately in circuits to control
or reduce the size of the current
• Resistance is measured in units called Ohms Ώ
• The relationship between voltage, current and resistance is known as
Ohm’s Law