# Physics - chapter 2

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What does the conservation of energy state?
Energy cannot be destroyed or created it can only be transferred into different types of energy.
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When can energy be useful?
Energy can only useful when it can be converted from one form to another
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Why is the efficiency of an appliance always less than 100%?
Because, some energy is always wasted and so all the input energy isn't transformed usefully
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What device are an exception to being 100% efficient?
Electric heater; because, all the electricity is converted to useful heat
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1) More efficient than a low energy light bulb. 2) Last even longer
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1) More expensive. 2) Don't give out as much light
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What are U-Values?
Is how fast heat can transfer through a material. The lower the U-Value, the better the insulator
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What is payback time?
The aount of time it takes for the initial cos,t to equal the money saved
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What is the formula for payback time?
Initial cost divided by annual saving
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What does draught proofing do?
Strips of foam and olastic around doors and windows. Which tops draughts of cold air from blowing in, they reduce heat loss due to convection
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What is a loft insulation?
A think layer of fibreglass wall laid out across, the loft floor and ceiling reduce heat by convection and conduction
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What is a cavity wall insulation?
Foam between bricks to reduce convection, conduction and radiation across the gap
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What does a thick curtain do?
Creates an air gap between the gap to reduce heat loss by convection and conduction
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Define specific heat capacity?
It is the amount of energy needed to raise the temperature to 1kg to a substance of 1°
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What is waters specific capacity?
4200 J/kg°c
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What are the units for specific heat capacity?
Measured in J/kg°c
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What are the units for temperature change?
Measured in °c
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What are the units for power?
W (watts)
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What are the units for energy?
J (joules)
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How to calculate cost of electrity?
1) energy transferred = power (in kW) x time (in hours) . 2) energy used (answer to step one) x price per unit
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How you convert kilowatts to watts?
times by 1000
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How do you convert watts to kilowatts?
divide by 1000
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What are non-renewable resources?
Non-renewable resources will run out one day
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What are renewable resources?
Renewable resources will never run out
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What are the four non renewable resources?
1) coal 2) oil 3) natural gas and 4) nuclear fuels (uranium and plutonium)
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1) emit greenhouse gases (e.g. CO2) 2) there supply is limited, will run out one day
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Cheap
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For a given amount of energy released, which fuel releases the most carbon dioxide?
Coal
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Which type of power station takes the least time to start up?
Natural gas
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Why are coal, oil and natural gas non-renewable resources?
Because, they cannot be replaced, except over millions of years
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1) Does not emit any greenhouses gases (e.g. CO2). 2) lots of energy released from a small piece of uranium and plutonium
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1) Radioactive material produced is hazardous to health for thousands of years. 2) Expensive to build
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Which type of power station takes the most time to start up?
Nuclear power stations
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How is nuclear energy released?
Through the process nuclear fission
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Name three types of renewable resources
Wind, solar, hydroelectric, geothermal, bio-fuels, tides
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1) No air pollutants released 2) No fuel cost
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1) Don't produce constant supply of electricity 2) Noise pollution 3) Visual pollution
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1) Immediate response to an increase demand in electricity 2) No greenhouse gases produced (e.g. CO2)
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1) Can effect wildlife 2) Initial costs are high 3) Can only be located in certain places
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1) No air pollutants released 2) low maitence
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1) unreliable sunlight varies 2) requires large surface area
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1) easily available 2) animal waste viable from farmer
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1) Releases C02 2) Expensive 3) large amount of land needed
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What is the national grid?
Distributes electricity from power stations to home
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What voltage do power-stations produce electricity at?
At 25000V
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What is the voltage used at homes?
At 230V
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What does the step down transformers do?
Decrease voltage and increase the current
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What does the step up transformers do?
Increase voltage and decrease the current
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Why do we increase the voltage?
To make the system more efficient
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What is the amplitude?
It is from the rest to the crest
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What is the wavelength?
Is from crest to crest
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What are the unit for amplitude in?
Metres (m)
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What are the unit for wavelength?
λ
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What are the units of frequency?
Hz
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1) Less expensive to set up 2) If there is faults easier to access 3) less
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1) Spoils landscape 2) Affected by severe weather e.g. storm 3) Greater risk of electric shock
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How to convert minutes into hours?
divide by 60
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how to convert seconds into hours?
divide by 3600
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Describe the directions on a longitudinal wave
In longitudinal waves the vibrations are parallel to the direction of energy transfer
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Describe the directions on a transverse waves
In transverse waves, the vibrations are perpendicular to the direction of energy transfer
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Give three examples of longitudinal waves
1) sound waves 2) shock waves 3) slinky spring
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Give three examples of longitudinal waves
1) electromagnetic waves 2) ripples on water 3) waves on strings
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What is the wave speed formula?
wave speed = frequency x wavelengh
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Say the electromagnetic wave
Radio waves, microwaves, infra-red, visible light, ultaviolent, x-rays and gamma rays
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Which type of EM wave has the highest energy?
Gamma rays
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Which type of EM wave has the the longest wavelength?
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Which type of EM wave has the shortest wavelength?
Gamma rays
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Which type of EM wave has the least energy ?
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Which type of EM wave has the lowest frequency?
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What speed do ALL electromagnetic waves travel at ?
300000000 (8 zeros!!)
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What do EM waves travel through?
Vacuum
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Which type of EM wave has the highest frequency?
Gamma rays
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Which type of EM wave is used in traditional photography?
Visible light
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What is the main use of gamma rays?
To sterilise food and medical equipment
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What is the main use of x-ray?
Used to check broken bones
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What is the main use of ultraviolet?
Absorbed by the skin for vitamin D
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What is the main use of visible light?
1) Enable us to see 2) In film and photography
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What is the main use of infra-red? (2)
1) remote controls 2) optical fibres
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What is the main use of microwave?
1) satellite TV 2) communication
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What is the main use of radio waves?
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What is diffraction?
The spreading out of waves when they pass a gap
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What is refraction?
When sound waves or light waves travel through a gap and changes direction
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Are soundwaves longitudinal or transverse?
Longitudinal
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How does the frequency of a sound wave affect the pitch of the sound?
The higher the frequency, the higher pitched the sound waves will be
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What type of waves do remote controls usually use?
Infra-red
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Why does light bend as it moves between air and water?
It refracts
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Why can't sound waves travel in space?
Becaus, in space it is mostly vacuum
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What does the red-shift observations tell us about the universe?
It tells us that the universe is expanding
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Describe the big bang theory
The universe was concentrated at a small point. This then began to enlarge rapidly in a hot explosion-the Big Bang began expanding and it is still expanding today
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What is an echo?
Reflection of sound
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Where does soundwaves travel faster at?
Solids and liquids
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Why are microwaves used for satellite communications?
1) Can travel through the earth without spreading out 2) Can penetrate the atmosphere to reach the satellite in space
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What is the Doppler affect?
Is the change in frequency of a wave for an observer moving relative to the source of the wave
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Give two evidence that supports the big bang theory
1) The light from other galaxies is red-shifted meaning universe is expanding 2) The Cosmic Microwave Background Radiation
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What is the Cosmic Microwave Background Radiation?
Is the remains of microwave energy created just after the Big Bang
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According to the Doppler effect, what happens to sound waves emitted at a constant pitch from a car moving towards you?
Their frequency increases, so their pitch increases
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Why is the light from distant galaxies red-shifted?
Shows that they are moving away from us
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Describe how the design of a vacuum flask keeps the liquid inside hot? (4)
1) Double walled with a vacuum between the two walls which stops all conduction and convection 2)The walls are silvered to keep heat loss by radiation to a minimum. 3) Supported using insulation foam, minimises heat conduction from the outer glass. 4
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What is a plane mirror?
A plane mirror is a mirror with a flat (planar) reflective surface.
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What does the law of reflection?
The angle of incidence equals the angle of reflection
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## Other cards in this set

### Card 2

#### Front

When can energy be useful?

#### Back

Energy can only useful when it can be converted from one form to another

### Card 3

#### Front

Why is the efficiency of an appliance always less than 100%?

### Card 4

#### Front

What device are an exception to being 100% efficient?