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science year 8
Science energy revision term 2
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Ava Swift
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Cards (32)
What is power defined as in physics?
Power is the amount of
energy
transferred each
second
.
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In which unit is power measured?
Power is measured in
watts
(W).
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What does a power rating of 100 watts indicate about a device?
It means that 100
joules
of energy are transferred each
second
.
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What is the relationship between kilowatts and watts?
1 kilowatt =
1000
watts.
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How can you calculate the energy transferred by an appliance using its power rating?
Use the formula:
Energy transferred
(J) =
Power
(
W
) ×
Time
(s)
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What is the formula to calculate energy transferred in joules?
Energy transferred
in joules (J) =
Power in watts
(W) ×
Time in seconds
(s).
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Why might some appliances have their power rating shown in kilowatts instead of watts?
Because they transfer large amounts of
energy
.
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How does the power rating of an appliance affect the energy transferred over time?
A
higher
power
rating results in
more
energy transferred in the
same
amount
of
time.
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What is work defined as in physics?
Work is done when a
force
causes an object to move.
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How is work related to energy in physics?
Work is a measure of the energy transferred when a
force
acts over a distance.
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In what situations is work done besides moving an object?
Work is done when a
force
compresses or extends a
spring
or other flexible object.
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What is the relationship between energy transferred and work?
Energy transferred = Work
Both are
measured
in
joules
(J)
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What unit is used to measure work and energy?
Joules
(J)
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What does it mean when work is done on a flexible object?
It means that a
force
is either compressing or
extending
the object.
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What is the formula for work done in joules (J)?
Work done (J) =
force (N)
x
distance (m)
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What is conduction?
Conduction is the flow of
heat energy
from high to low
temperature
without overall movement of material.
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Which materials are considered good conductors of heat energy?
Metals
are good conductors of heat energy.
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What are poor conductors of heat called?
Poor conductors of heat are called
insulators
.
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How are atoms in a solid held together?
The atoms of a solid are held together by
chemical bonds
.
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What happens to atoms in a solid when they absorb heat energy?
They vibrate faster and with bigger
amplitude
.
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How does heat energy transfer in solids?
Heat energy transfers from
atom
to atom through vibrations.
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Why is conduction in metals faster than in non-metals?
Conduction in metals is faster due to
free electrons
and collisions with
metal ions
.
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What are free electrons in metals responsible for?
Free electrons in metals are responsible for good
thermal conductivity
.
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What is convection?
Convection is the flow of heat energy by movement of a
fluid
from high to low
temperature
.
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What types of materials are considered fluids?
Liquids
and
gases
are considered fluids.
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How does convection occur in fluids?
Convection occurs when particles with high
heat energy
move and replace particles with less heat energy.
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Why is water heated from the bottom in kettles and saucepans?
Water is heated from the bottom to easily set up
convection currents
.
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What happens in a lava lamp during convection?
The wax warms up, expands, becomes less dense, and rises, creating
convection currents
.
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What are the processes involved in conduction in metals?
Collisions between fast-moving
free electrons
and
metal ions
Passing vibrations
from atom to atom
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What are the characteristics of good insulators?
Poor
conductors
of
heat
Traps
air
(e.g., trapped air, hair, fur, feathers, wool)
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What is the difference between conduction in metals and insulators?
Metals: conduction by free electrons and vibrations
Insulators
: conduction only by passing vibrations
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How does heat transfer occur in a beaker heated by a Bunsen flame?
Heat is transferred by
conduction
through the glass.
Water near the flame heats up.
Convection currents
are set up in the water.
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