Physics Flashcards
The hotter an object is the more infrared radiation …
… It radiates in a given time
Black, matte surfaces are …
… Good absorbers and emitters of infrared radiation (heat)
Light, shiny surfaces are …
… Poor absorbers and emitters of infrared radiation but good reflectors
Kinetic theory is used to …
… Explain the different states of matter
Particles of solids, liquids and gases have …
… Different amounts of energy
What are particles involved in
The transfer of energy by conduction, convection, evaporation and condensation
What do all objects emit and absorb
Infrared radiation
What is conduction
When the particles/free electrons/ atoms at the hot and gain energy and vibrate faster. They then pass on their extra kinetic energy and heat to neighbouring particles/atoms/free electrons through diffusion and collision.
What is convection currents
The heated particles becomes less dense therefore rising. The warm air displaces the cooler air and the cool denser air falls.The cool, denser air flows to fill the gap left by the rising, heated air
What is evaporation
Evaporation is when particles escape from the liquid.
What is condensation
When gas cools, the particles in a gas slow down and lose kinetic energy. The attractive forces between the particles pull them closer together. If the temperature gets cold enough and the gas particles get close enough together that condensation can take place, the gas becomes a liquid.
Factors affecting the rate of evaporation
Temperature (higher temperature = faster rate) Density (lower density = faster rate) Surface area (larger surface area = faster rate) Airflow over the liquid (greater airflow = (faster rate)
Factors affecting the rate of condensation
Temperature of the gas (lower temperature = faster rate)
Temperature of the surface the gas touches (lower temperature = faster rate)
Density (higher density = faster rate)
Airflow (less airflow = faster rate)
The rate at which an object transfers energy by heating depends on
Surfaces area and volume
The material from which the object is made
The nature of the surface with which the object is in contact
The bigger the temperature difference between an object and its surrounding…
… the faster the rate at which energy is transferred by heating
What does U-value measure
What does U-value measure
The lower the U-value …
… The better the material is as an insulator
What do certain solar panels contain
Water that is heated by radiation from the sun. This water may then be used to heat buildings or provide domestic hot water
What is the specific heat capacity of a substance
The amount of energy required to change the temperature of 1 kg of the substance by 1°C
Energy transferred = mass x specific heat capacity x temperature change
What is the conservation of energy principle
Energy can be transferred usefully, stored, or dissipated, but cannot be created or destroyed
When energy is transferred …
… Only part of it may be usefully transferred, the rest is ‘wasted’
Wasted energy is eventually…
… transferred to the surroundings, which become warmer. The wasted energy becomes increasingly spread out and so becomes less useful
How do you calculate the efficiency of the device
Efficiency = useful energy out /total energy in * 100
What are the differences between the three states of matter
The arrangement and energy of the particles
What happens when you heat a substance
You give its particles more kinetic energy so they vibrate or move faster
How do you know whether a material is a conductor
Conductors are usually dense solids. Their particles are closer together and so collide more often and pass energy between them. This allows conduction to happen faster therefore they are conductors
How do you know whether a material is an insulator
Insulators are materials that have larger spaces between their particles so they conduct heat much more slowly.
How do you calculate payback time
Payback time = initial cost / annual saving
How does cavity wall insulation reduce heat loss
The foam squirted into the gaps between the bricks reduces convection and radiation across the gap. Pockets of air in the foam reduce heat transfer by conduction
How does loft insulation reduce heat loss
The thick layer of fibreglass wool laid out across the loft floor and ceiling reduces heat loss from the house by conduction and convection
How does draught proofing reduce heat loss
The strips of foam and plastic around doors and windows stop draughts of cold air blowing in. This reduces heat loss due to convection.
How do hot water tank jackets reduce heat loss
The fibre glass wool reduces conduction and radiation
How do thick curtains reduce heat loss
It reduces heat loss by convection and conduction
The amount of energy an appliance transfers depends on …
… How long the appliance is switched on and its power
How do you calculate the amount of energy transferred from the mains
E= P*t
Energy transferred in kWh = power in kW * time in h OR
Energy transferred in J = power in w * time in s
What are the different types of energy
Electrical Light Sound Kinetic Nuclear Thermal Gravitational potential Elastic potential Chemical
What is stored energy
Energy waiting to be turned into one of the other forms e.g. Potential and chemical
When is energy useful
When it can be converted from one form to another
What happens in a power station
An energy source is used to heat water. The steam produced drives a turbine that is coupled to an electrical generator
What are some energy sources used in power stations
The fossil fuels (coal, oil &gas) which are burned to heat water or air
Uranium and plutonium, when energy from nuclear fission is used to heat water
Biofuels that can be burned to heat water
Renewable energy resources
Wind Waves Tides Hydroelectric Solar Geothermal Food Biofuels These sources can be used to drive turbines directly
How do solar cells work
Solar cells generate electric currents directly from the Sun’s radiation
Using different energy resources has different effects on the environment. These effects include
The release of substances into the atmosphere
The production of waste materials
Noise and visual pollution
The destruction of wildlife habitats
What is carbon capture & storage
A rapidly evolving technology that works by collecting the CO2 from power stations before it is released into the atmosphere. The captured CO2 is then pumped into empty gas fields and oil fields, like those under the North Sea
What is potential difference
Voltage
What does the National Grid do
Distribute electricity from power stations to consumers
Essential parts of National Grid
Power station - step-up transformer - pylons - step-down transformer - consumers
What are the use of transformers
The transformers have to step up the voltage up at one end, for efficient transmission, and then bring it back down to safe, usable levels
What are the different ways to transmit electricity
Overhead cables
Underground cables
What do waves do
Transfer energy
Features of waves
Amplitude
Wavelength
Crest
What is amplitude
The displacement from the rest position to the crest
What is the wavelength
The length of a full cycle of the wave e.g. from crest to crest or trough to trough
What is frequency
The no. of complete waves passing a certain point per second OR the no. of waves produced by a source each second
What is frequency measured in
Hertz (Hz). 1 Hz is one wave per second
Types of waves
Transverse
Longitudinal
Examples of transverse waves
All Electromagnetic waves
Ripples
What do transverse waves have
Sideways vibrations. In transverse waves the vibrations are perpendicular (90 degrees) to the direction of energy transfer of the wave
What do longitudinal waves have
Vibrations along the same line. In longitudinal waves the vibrations are parallel to the direction of energy transfer of the wave. They also have areas of compression and rarefactions
What is the calculation for wave speed
Speed = Frequency * Wavelength
(m/s) = (Hz) * (m)
OR
v = f * lamda
Examples of longitudinal waves
Sound waves
Shock waves e.g. seismic waves
Mechanical waves may be …
… either transverse and longitudinal
All types of electromagnetic waves travel …
… at the same speed through a vacuum (space)
What do electromagnetic waves form
A continuous spectrum
What is the order of the electromagnetic spectrum and their wavelengths
Radio waves (1m - 10 4) Micro waves (10 -2) Infrared (10 -5) Visible light (10 -7) Ultra violet (10 -8) X-Rays (10 -10) Gamma Rays (10 -15) The longer the wavelength, the lower the energy and frequency
Waves can be …
…reflected, refracted and diffracted
When does significant diffraction occur
When the wavelength of the wave is of the same order of magnitude as the size of the gap or obstacle
What happens when waves are refracted at an interface
They undergo a change in direction. Waves are not refracted if travelling along the normal
What type of waves can be used for communication
Radio waves, microwaves, infrared and visible light
What are radio waves specifically used for
Television and radio
What are micro waves specifically used for
Mobile phones and satellite television
What is infrared specifically used for
Remote controls - They work by emitting different patterns of infrared waves to send different commands to an appliance e.g. a TV
What is visible light specifically used for
Photography
What is Cosmic Microwave Background Radiation (CMBR)
A form of electromagnetic radiation filling the universe. It comes from radiation that was present shortly after the beginning of the universe
What is the normal
A construction line perpendicular to the reflecting surface at the point of incidence
The angle of incidence is …
… equal to the angle of reflection
Rules about drawing a ray diagram
- ) The image is the same size as the object
- ) It is as far behind the mirror as the object is in front
- ) The image is virtual and upright in the plane mirror
- ) The image is laterally inverted - the left and right sides are swapped
What is diffraction
When waves spread out at the edges when they pass through a gap or pass an obstacle. The amount of diffraction depends on the size of the gap relative to the wavelength of the wave. The narrower the gap, or the longer the wavelength, the more the wave spreads out.
What is refraction
A wave refracts when it meets a different medium at an angle and therefore changes direction
How does red shift help prove the ‘Big Bang’ Theory
It shows that other galaxies are moving away from us and that the whole universe is expanding. This supports the theory that the start of the universe could have been from a single explosion.
What are sound waves
Longitudinal waves that cause vibrations in a medium, which are detected as sound
What is the pitch of a sound determined by
Its frequency
What is the loudness of a sound determined by
Its amplitude
What are echoes
Reflections of sound
What is the Doppler Effect
When a source that emits waves (either light, sound or microwaves), the wavelengths and frequency seem different - compared to when the source is stationary.
The frequency of a source moving towards you will seem higher and its wavelength will seem shorter. The frequency of a source moving away from you will seem lower and its wavelength will seem longer
What is red-shift
Different chemical elements absorb different frequencies of light. Each element produces a specific pattern of dark lines at the frequencies that it absorbs in the visible spectrum. When we look at light from distant galaxies we can see the same patterns but at slightly lower frequencies than others - they’re shifted towards the red end of the spectrum
More distant galaxies have greater red shifts than nearer ones
How does CMBR help prove the ‘Big Bang’ theory
The relatively uniform background radiation is the remains of energy created just after the Big Bang.
