Heat, Light and Sound
• Temperature – measured with a thermometer.
• Heat – is described as the total energy of all
particles within an object.
• 2L of water at 100°C has more energy than 1L
of water at 100°C . It has twice as many
particles and therefore, twice as much heat
1L of water will heat quicker than 2L because
there are fewer particles. The particles each
absorb more energy and move faster.
• Is an indicator of how hot or cold something is.
• Hotter substances have particles that are
moving faster (more kinetic energy) than cooler
• Liquids expand when heated and contract
when cooled – this is how a glass
• Temperature is measured in degrees Celsius
°C, degrees Fahrenheit °F, and Kelvin K.
• Heat flows from areas of higher temperature
to areas of lower temperature.
• The greater the temperature difference the
faster the heat flows from one object to
• Is heat transfer by vibrating particles.
– Heat from warm objects melts ice.
– A hot mug transfers heat to hands.
• Conductors (e.g. copper wire) and insulators
• When air is heated the particles have more
energy and move apart.
• Hot air is less dense than cool air – hot air
• The transfer of heat energy from the Sun is by
• Radiation transmits heat as waves at the
speed of light.
• All objects release infra-red radiation – the
hotter something is the more heat is radiates.
• Dark coloured objects are good absorbers of
heat e.g. a black car.
• Light coloured objects reflect more radiation
and heat slower.
• Clear materials such as glass transmit radiated
• Sound is produced when something vibrates.
• A sound wave occurs when air particles
alternate between being bunched together
(compression) and spread out (rarefactions).
• Sound waves rely on particles – either a solid,
liquid or gas.
• Transverse wave e.g. how an ocean wave
travels to the shore while a boat just moves up
• Longitudinal wave – Sound wave i.e. the
particles that make up the wave move in the
same direction the wave is travelling.
Speed of Sound
• Sound travels faster through a solid than a
liquid, and faster through liquids than gases.
– Think about the number of particles in each.
• Hard surfaces reflect sound – echo. Soft
surfaces absorb sound and convert it into
Frequency and Pitch
• A source that vibrates rapidly produces sound
of higher pitch (frequency).
• Frequency of a wave is the number of
vibrations a sound makes per second.
• Frequency is measured in Hertz, Hz.
• Wavelength is the distance between
successive peaks (measured in metres).
• Ultrasound – sound waves with frequencies
above our hearing range.
• Infrasound – lower than our hearing range.
• Light is a form of energy known as
• Light travels as an electromagnetic wave.
• Light travels through the vacuum of space –
• It travels at
300 000 km/s
• Light can be transmitted through transparent
material (glass), reflected through translucent
material (paper), and reflected or absorbed by
opaque material (brick wall).
• Luminous objects emit light.
Most objects do not produce there own light.
You see them because light bounces off them
and into your eyes.
When viewing yourself in a flat mirror your
reflection appears reversed. This is known as
• Refraction occurs when light travels from one
transparent substance into another e.g. air to
• Light is bent when it travels from water into
• Light travels at different speeds through
difference substances – bending or refraction
of light as it passes from one substance to
• The refractive index is a measure of how easily
light travels through different substances.
• Light travels more slowly through glass and
diamonds, than air.
Convex lenses cause light rays to converge.
Concave lenses cause light rays to diverge.
How We See
In the eye, refraction occurs when light passes
from the air to the cornea, from the cornea to
the aqueous humor, from the aqueous humor to
the lens and from the lens to the vitreous
humor. Light spreading out from one point on an
object can therefore be focused on a particular
point on the retina.
The wavelengths can be detected by the light-sensitive
cells called rods and cones present in
Cornea - The cornea is the transparent
membrane which forms the outer coating at the
front of the eyeball and covers the iris and pupil.
It also focuses light on the retina.
Retina - is the light-sensitive inner lining of the
back of the eye. Rays of light enter the eye and
are focused on the retina by the cornea and
lens. The retina produces an image which is sent
along the optic nerve for the brain to interpret.
Lens - a transparent body
behind the iris. The lens
bends light rays so that they
form a clear image at the
back of the eye – on the
retina. As the lens is elastic,
it can change shape, getting
fatter to focus close objects
and thinner for distant
• See objects that are close clearly but objects
in the distance are out of focus.
• Rays from distant objects are focused in front
of the retina rather than on the retina.
• The usual cause of myopia is that the eyeball
is too long. Some forms of myopia improve
• See objects that are in the distance clearly but
close objects are out of focus.
• Rays from distant objects are focused behind
the retina rather than on the retina.
• The usual cause of hyperopia is that the
eyeball is too short or that the lens gradually
hardens with age, reducing its power of