Physics end of year

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  • Created by: Izzybc
  • Created on: 31-05-15 14:00
Describe the arrangement of particles in a solid
- Regular, close arrangement; -particles vibrate about fixed positions; -solid stays in shape
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Describe the arrangement of particles in a liquid
-irregular arrangement, particles held close together; -vibrate more, move around randomly; -Fill the bottom of the container
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Describe the arrangement of particles in a gas
-particles are widely spaced, random movement; -very high energy, fast movement; -fill whole container
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Where does conduction occur?
In solids, particularly metals
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What is a thermal insulator?
A poor conductor of heat
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Explain what happens during conduction
When one part of a solid is heated, the temperature of the particles there increases, and they gain kinetic energy, they vibrate faster and further, particles collide with their neighbours making them vibrate more. They transfer their kinetic energy
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Why are air and water good insulators?
They conduct heat much more slowly than solids, as their particles aren't held so tightly together
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Explain why a piece of metal left outside in the cold feels colder than a piece of wood
The metal and the wood are the same temperature- however, because metal is a better conductor of heat, heat is conducted away from your hand quicker, making your hand feel cold
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Explain what happens during convection
When one part of a fluid is heated, the particles there gain kinetic energy and move further apart. The fluid becomes less dense in that particular region and rises, being replaced by cooler fluid. This is called a convection current
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Does heat radiation require particles?
No- heat radiation can occur through a vacuum, for example- heat reaches earth from the sun despite the vacuum of outer space
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Complete this sentence: An object that is hotter than its surroundings...
...emits more radiation than it absorbs (cools down)
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Complete this sentence: An object that is cooler than its surroundings...
...absorbs more radiation than it emits (warms up)
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Does a larger surface area cause heat to be radiated slower or quicker?
Heat is radiated away quicker: the bigger the surface area, the more infared waves can be emitted from the surface (heat is radiated from the surface of an objce)
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Why do car engines have cooling fins?
they increase the surface area so that heat is radiated away quicker- keeping the engine cool
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Do dark surfaces absorb or reflect infared radiation?
they absorb infared radiation and get warmer
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Do white/ shiny surfaces absorb or reflect infared radiation?
They reflect infared radiation
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Why is a motorcycle with a black engine cooler than a motorcycle with a shiny engine?
Dark surfaces are better emitters of heat radiation, so the heat is radiated away quicker, making the engine cooler
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What can be done to maximise the rate of energy transfer?
-large temperatue difference between object and suroundings, -large surface area, -dull black surfaces, -maximise air flow, -object is a good conductor
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What can be done to minimise the rate of energy transfer?
-object is a good insulator, -white shiny surfaces, -air trapped in small pockets to reduce convection (trapped air cannot move around in a convection current) -vacuum to stop energy transfer by conduction and convection
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What is the difference between boiling and evaporation? pt 1
BOILING occurs when the molecules are able to escape from all parts of the liquid. Occurs at the boiling point of a liquid. For example when water reaches b pt (100 degrees C) bubbles of water vapour from anywhere in the liquid rise to the surface
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What is the difference between boiling and evaporation? pt 2
EVAPORATION takes place at the surface of the liquid pver a range of temperatures lower than boiling point
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What effect foes heat have on the rate of evaporation?
The evaporation rate is increased as more molecules in the liquid have enough energy to escape
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Name four factors that increase the rate of evaporation
1) higher temperature, 2) large surface area, 3) lower humidity 4) breeze across surface of the liquid
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Why does humidity decrease the rate of evaporation?
lots of moisture already in the air and it would be difficult for more moisture to evaporate as there is little room
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Why does evaportation cause cooling? pt 1
1) When a liquid evaporates, molecules leave the surface of the liquid 2) these molecules must overcome the bonds between them and the other molecules 3) so only the particles with the largest amount of energy are able to escape from the liquid
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Why does evaportation cause cooling? pt 2
4) therefore the molecules that remain in the liquid will have a lower average temperature (lower amount of energy)
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Why do you feel cold after getting out of the swimming pool?
The liquid on your skin absorbs energy from your skin so that the liquid particles have enough energy to evaporate. Our body temperature drops- as we transfer energy to the cool liquid
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When does condensation occur?
condensation occurs when water vapour turns back into a liquid as it hits a cool surface
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What happens in condensation in terms of particles?
When the gas particles lose energy they move more slowly, come closer together and turn back into a liquid state
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Name 2 factors that increase the rate of condensation
1) large difference in temp, 2) cold surface has a large area
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How does the vacuum flask minimise the rate of energy transfer?
1) vacuum between the walls of the double glass container to prevent heat energy transfer by conduction and covection, and "silvering" on the glass surfaces to reduce energy transfer by radiation
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Why does this happen?
When heat is applied, the particles in the gas gain more kinetic energy, and the particles in the gas move further apart. This causes the volume of gas to expand and escape through the tubing
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What happens when the flask is no longer heated?
The bubbles no longer rise from the tubing, this is because heat is no longer provided, so the volume of air contracts and occupies less space in the tube. This allows room for the water to be sucked throught the tube
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What happens when the ball is heated in the ball and ring experiment whent the ball is heated?
Th ball can no longer fit through the ring. This is because the silid particles gain more energy and spread further apart, causing the metal to expand
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What happens when a bimetallic strip is heated?
The outer metal (usually brass- as the bonds between the brass particles are weaker) expands more than the inner metal (iron) causing the strip to bend with the brass on the longest side as they are riveted together
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How does the bimetallic strip help a thermostat work? pt 1
The strip works as abridge in an electrical circuit connected to your heating system. When the bridge is down, the strip completes the circuit and the heating is on.
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How does the bimetallic strip help a thermostat work? pt 2
However, because the strip is getting hotter with the high temperature, it eventually bends so much that it breaks the circuit, and the heating is no longer on
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How does turning the control knob change the temperature at which the circuit switches on and off?
Because the circuit is connected to the bimetallic strip, when twisted, it can apply pressure to the bimetallic strip (making it harder for the strip to bend away) and therefore completing the circuit for longer
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How do rollers prevent damage to bridges?
They allow for the bridge to contract in cool weather without damaging the system. They act as a sterdy set of wheels, allowing the upper system to roll back and forth
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Where can expansion by heating cause problems?
Expansion by heating can cause problems in train tracks- as the heat causes them to expand and place a lot ofstress on the anchors that hold them down. Eventually, these tracks buckle under the stress.
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How can these be overcome?
This can be overcome by having overlapping gaps in the tracks to allow room for the expansion to take place
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Other cards in this set

Card 2

Front

Describe the arrangement of particles in a liquid

Back

-irregular arrangement, particles held close together; -vibrate more, move around randomly; -Fill the bottom of the container

Card 3

Front

Describe the arrangement of particles in a gas

Back

Preview of the front of card 3

Card 4

Front

Where does conduction occur?

Back

Preview of the front of card 4

Card 5

Front

What is a thermal insulator?

Back

Preview of the front of card 5
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