heat, light and sound
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Year 9 Heat, Light and Sound - For additional resources visit: http://www.iheartscience.netTRANSCRIPT
Heat, Light and SoundSarah Jones
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Heat• 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 energy.
1L of water will heat quicker than 2L because there are fewer particles. The particles each absorb more energy and move faster.
Temperature• Is an indicator of how hot or cold something is.• Hotter substances have particles that are
moving faster (more kinetic energy) than cooler substances.
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• Liquids expand when heated and contract when cooled – this is how a glass thermometer works.
• Temperature is measured in degrees Celsius °C, degrees Fahrenheit °F, and Kelvin K.
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Heat Transfer• 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 another.
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Conduction• 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 (e.g. rubber).
Convection• When air is heated the particles have more
energy and move apart.• Hot air is less dense than cool air – hot air
rises.
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Radiation
• The transfer of heat energy from the Sun is by radiation.
• 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.
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• 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 heat.
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Sound• 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 and down.
• Longitudinal wave – Sound wave i.e. the particles that make up the wave move in the same direction the wave is travelling.
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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 heat.
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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.
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• 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• Light is a form of energy known as
electromagnetic radiation.• Light travels as an electromagnetic wave.• Light travels through the vacuum of space –
unlike sound.• It travels at 300 000 km/s
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• 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.
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The Law of Reflection
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Plane MirrorsWhen viewing yourself in a flat mirror your reflection appears reversed. This is known as lateral inversion.
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Refraction• Refraction occurs when light travels from one
transparent substance into another e.g. air to water.
• Light is bent when it travels from water into air.
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• Light travels at different speeds through difference substances – bending or refraction of light as it passes from one substance to another.
• 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
Convex lenses cause light rays to converge.
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Concave Lenses
Concave lenses cause light rays to diverge.
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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 the eye.
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.
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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 objects.
Myopia• Short-sightedness • See objects that are close clearly but objects
in the distance are out of focus.
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• 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 with age.
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Hyperopia
• Long-sightedness• 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 accommodation.
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