# Physics Revision

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• Created by: pvibrans
• Created on: 13-05-15 18:43
How does evaporation cause the cooling of water?
The most energetic molecules leave the surface of liquid during evaporation. This means that the average kinetic energy in liquid is less. Temperature depends on average kinetic energy therefore is reduced.
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The mass of water in a cup is 200 g. Calculate the energy (in joules) transferred from the water in the cup when the temperature of the water falls by 8 degrees. SHC= 4200 J/kg degrees.
E= mcϑ so 200 x 4200 x 8= 6, 720, 000 Joules.
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How does the vacuum in the vacuum flask help reduce heat transfer?
It reduces heat transfer by both conduction and convection because it has no particles.
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How does the silvered inner surfaces of the vacuum flask help reduce heat transfer?
It prevents heat transfer by radiation as it reflects the infrared rays back so the heat energy stays inside. Also, light shiny surface= good reflector.
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How does the plastic and the double-walled container of the vacuum flask help reduce heat transfer?
They both prevent heat transfer by conduction as plastic and glass are good insulators and a poor conductors.
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All objects emit _________ and absorb thermal radiation.
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The ________ an object is the more energy it radiates in a given time.
hotter.
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______, _______ surfaces are good absorbers and good emitters of radiation/
black, matt.
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______, _______ surfaces are poor absorbers and poor emitters, but good reflectors, of radiation.
light, shiny.
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Describe the process of condensation.
Condensation happens when a gas cools down. Energy is released. Particles become closer together. Form stronger bonds. Happens faster if the temperature is colder.
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the higher the wind speed, the ______ the evaporation.
faster.
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The higher the temperature, the ________ the evaporation.
faster.
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The higher the humidity, the _______ the evaporation.
slower.
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(1) Convection currents occur in _____ and _____ because their particles move _____ when they are hot causing the liquid or gas to _____. When particles move apart they make a fluid less ______.
Gases, liquids, apart, expand, dense.
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(2) Warm regions are then less ______ than cold regions. The warm fluids _____ through the colder ones and colder fluids replace the warmer ones which have risen.
dense, rise.
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Explain the process of conduction through metals.
The water particles gain energy. The particles vibrate more, so they collide with each other. The vibrations pass on. The free electrons help carry on the energy.
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Radiation: Can move through a _____. Heat energy transferred as a ____. ____, _____ surfaces are the best absorbers and emitters of heat. ____, ____ surfaces are the best reflectors of heat.
vacuum, wave, dark, matt, light, shiny
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Name all the types of energy. (Most Kids Hate Learning GCSE Energy Names!)
Magnetic, Kinetic, Heat/Thermal, Light, Gravitational Potential, Chemical, Sound, Electrical, Elastic Potential, Nuclear.
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Name the Electromagnetic spectrum. (Granny X's Umbrella Vanishes In Mild Rain!)
Gamma, X-Rays, Ultraviolet, Infra-Red, Microwaves, Radio waves
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What is diffraction?
The spreading out of waves through a gap. If gap>wavelength then we get small diffraction. If gap=wavelength then we get the most diffraction.
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1) The farmers in a village in India use solar powered water pumps to irrigate fields. A 1 sqm panel of solar cells receives 5 kWh from the sun every day. Efficiency of 0.15. Calculate the electrical energy available from 1 sqm panel of solar cells.
Efficency=useful energy out/total energy in. 0.15 x 5 = 0.75. energy = 0.75 kWh.
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2) Each solar water pump uses 1.5 kWh of energy each day. Calculate the area of solar cells required by one solar water pump.
1.5 / 0.75 = 2. Two solar panels are required.
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How can the heat loss through the windows of a house be reduced?
Double - glazing or curtains.
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What is the amplitude of a wave?
the distance of the bottom to the top of one wave.
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What is the frequency of a wave?
The width of the wave.
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Which one of the following statements is true for electromagnetic waves travelling through a vacuum? a) all the waves have the same frequency b) all the waves have the same wavelength c) all the waves travel at the same speed
c) All the waves travel at the same speed.
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What serious health problems can be caused by exposure to the UV radiation from the sun?
Skin cancer/damage to the skin.
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Calculate the speed of a sound wave with a frequency of 250 Hz and a wavelength of 1.3 m.
wave speed = frequency x wavelength. 250 x 1.3 = 325. Speed = 325 m/s.
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Which type of electromagnetic wave is used to communicate with a satellite in space?
Microwaves.
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Which four types of electromagnetic waves are used for communication?
Visible light, Infra red, Microwaves and Radio waves.
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Astronauts in space cannot hear sounds from outside their spacesuits. Why?
There are no air particles in space, therefore the sound waves will not be able to travel to the astronaut because waves need particles to travel.
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What happens to a ray of light travelling through a glass block?
It speeds up when travelling through the air and slows down when travelling through the glass.
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Angle of _______= Angle of Refraction
Incidence
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Describe the energy transfers which occur as an electric light bulb is used: ______ energy is transferred into ______ energy and ______ energy.
Electric, light, heat.
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An electric motor is designed to transform electrical energy into ______ energy. Some of the electrical energy supplied to the motor is wasted as ______ energy and ______ energy.
kinetic, sound, heat.
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A metal pan is being used to heat water. Energy from the gas flame is transferred through the metal pan by conduction. Explain the process of conduction through metals.
The water particles gain energy from the flame. The particles collide with each other and vibrate faster, so the vibrations pass on. The free electrons in the metal help carry on the energy.
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Plastic foam is good at reducing heat loss through the walls of a house. Why?
It contains pockets of trapped air. Air is a good insulator so it will keep the heat energy inside the house. The plastic prevents convection currents from forming and reduces conduction. Plastic is also a good insulator.
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Transverse waves are _______ to the direction of energy transfer. Longitudinal waves are _______ to the direction of energy transfer.
perpendicular, parallel
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A musical note with a high frequency sounds ______ than one with a low frequency.
higher
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A noise of small amplitude sounds ______ than one with a large amplitude.
quiter
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## Other cards in this set

### Card 2

#### Front

The mass of water in a cup is 200 g. Calculate the energy (in joules) transferred from the water in the cup when the temperature of the water falls by 8 degrees. SHC= 4200 J/kg degrees.

#### Back

E= mcϑ so 200 x 4200 x 8= 6, 720, 000 Joules.

### Card 3

#### Front

How does the vacuum in the vacuum flask help reduce heat transfer?

### Card 4

#### Front

How does the silvered inner surfaces of the vacuum flask help reduce heat transfer?

### Card 5

#### Front

How does the plastic and the double-walled container of the vacuum flask help reduce heat transfer?