Physics topic 9 Light

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  • Created by: asch
  • Created on: 27-05-14 18:48
What does temperature tell us?
How hot something is
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what do we use to measure temperature?
a thermometer
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What do units do we measure temperate in today?
degrees celcius
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What is heat?
heat is a form of energy.
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What does the amount of energy needed to heat something depend on?
how much is being heated, what it is made of and the temperature you want it to be.
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How does heat flow?
Heat always flows from a hotter to a colder object.
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What then happens to these objects?
the hotter objects cool down and the cooler objects warm up.
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What do you do when you heat something?
you transfer energy to its particles and they move faster.
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What do the particles do in a solid when they are heated?
In a solid they vibrate more!
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what do the particles do in liquids or gases when they are heated?
they move around faster. This means the temperature increases.
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Why do you feel a breezing blast of air if you open a window on a cold night?
Its not the cold rushing in its the heat fishing out from your nice warm room.
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What is conduction?
conduction is the way heat is transferred in a solid.
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What are the best conductors by far?
metals
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Which metal is especially good at conducting heat?
copper
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why do expensive saucepans often have copper bottoms?
to quickly conduct heat throughout the base to the food inside.
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What non metals are bad conducers of heat?
things like paper, cloth, wood and plastic.
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What do we call them if they are bad conductors of heat?
thermal insulators
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what is another bad thermal conducer?
air.
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Why do things like duvets and ski jackets keep us warm?
its because they are made from padded material that traps lots of air between its fibres. This makes it a good insulator.
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Why is carpet a good insulator?
because the heat energy is stored between and cannot escape.
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Why are bathroom tiles good thermal conductors?
it means the energy stored in your feet is conducted away by the tiles leaving your feet cold.
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Feeling cold is always due to.... what?
losing heat not gaining cold.
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how can we explain conduction?
by thinking about what is happening to the particles in a solid!
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What are the particles in a solid like?
The particles in a solid are close together and are arranged in a regular pattern. They vibrate on the spot.
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What does heating the solid do?
heating the solid at one end transfers energy to the particles there and they vibrate more. They bump into nearby particles transferring energy to them and making them vibrate more. These then bump into particles further along.
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Why is this good?
because in this way heat energy is transferred quickly to the other end of the solid!
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Why are some metals better conductors than others?
Their particles are closer together so they transfer energy more quickly.
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What are bad conductors of heat called?
insulators!
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how is heat transferred in liquids and gases?
by convection
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What is convection?
convection is the rising of warm air through colder air.
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What is a convection current?
Its when warm spots on the ground heat the air above and this warm air rises. Colder air falls towards the ground where it is heated. This movement of warm and cool air creates a convection current.
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What uses convection currents.
birds and gliders.
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When planes separate with the glider what are the two things they use?
They use convection currents when they separate and the glider uses thermals to stay in the air.
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How can we use a glass tube to show how convection works in liquids?
because some water at the top is coloured with dye. The tube is then heated at one corner. The dye spreads around the tube.
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Why does the dye spread around the tube?
The water near the flame gets hot and expands because the particles in the hot water move faster and get further apart. The water becomes less dense and rises. Cooler denser air takes its place. The water gets heated and so on. The dye is all around.
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When do we use convection currents?
a lot in our everyday lives!
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What does an electric kettle rely on?
on convection currents to heat all the water inside it. The heating element in the kettle is at the bottom and this sets up a convection current.
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In a fridge why is the freezing compartment mostly always placed at the top?
so that convection current keep the whole fridge cold.
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Are liquids and gases good or bad conductors of heat?
poor
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What happens if you heat a metal object?
it will heat up
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what happens if you heat a liquid from the top?
only the liquid at the top would boil
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what do convection currents have?
lots of uses.
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what is a thermogram?
a record of the image made by a thermal imaging camera.
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What does a thermogram show?
Its shows the temperature on their surfaces?
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How is the temperature scale colour coded?
from dark to blue ( coldest ) though red to white ( warmest )
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Why can we see the temperature of an object!
because hot objects give off fared radiation
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what is infrared radiation
a wave like light.
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where do both infrared and light come from?
the sun. You see the sunlight but you cannot see infrared radiation but you can feel it.
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how far is the sun from the earth?
150 million km away.
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why can't the sun reach the earth buy conduction or convection?
its because there is a lot of empty space with no air particles in-between.
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whats another word for gives out?
emits
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what do hot objects emit?
heat energy as radiation.
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what happens to the more energy it radiates if it the object is hotter?
the hotter the object the more energy it radiates?
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do we give out infrared?
yes
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if you put your hand near the fire or iron what do you feel?
you can feel the infrared radiation from it!
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What do thermal imaging cameras do?
they detect infrared radiation given out by warm objects and produce thermograms.
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why dont we paint our central heating radiators black?
because radiators actually heat a room manly by convection.
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what do shiny surfaces do?
they are bad at emitting and absorbing infrared, they reflect it.
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what do matt black surfaces do?
they are good at emitting and absorbing infrared.
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what do objects do all the time?
they give out and take in heat energy all the time. the hotter the object the more heat it gives out.
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why does energy move from a warm place to a cold place?
because of the difference in temperature between them. The energy transfer is always from hot to cold.
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how can energy be transferred?
by conduction, convection and radiation and often all three together.
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what does a vacuum do?
it reduces energy transfer to or from the air outside by conduction, convection or radiation.
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what does a vacuum have.
no particles inside of any kind this reduces transfer by any of the three.
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what does a light bulb transfer?
it transfers energy from electricity to light. But the bulb gets hot so some electrical energy is also transferred to heat which transfers to the air.
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what do you call energy you can't use again?
wasted air.
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whats a word equation for total energy?
total energy input = total energy output.
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what do we measure energy in?
joules ( j)
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what do sankey diagrams show?
they show the energy transfers in a process.
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What are some features of a sankey diagram?
the thicker the arrow the more amount of energy is transferred.
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does energy always exist?
yes it does however once it has spread out in the air it brings no use to anyone!
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can energy be gained or lost?
no it can only be changed from one form to another!
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Other cards in this set

Card 2

Front

what do we use to measure temperature?

Back

a thermometer

Card 3

Front

What do units do we measure temperate in today?

Back

Preview of the front of card 3

Card 4

Front

What is heat?

Back

Preview of the front of card 4

Card 5

Front

What does the amount of energy needed to heat something depend on?

Back

Preview of the front of card 5
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