P1 Flashcards
Heat energy only flows in which direction?
From hotter objects to colder objects.
When do things cool down the fastest?
When there is a big difference in temperature.
What is a thermogram?
A picture where different colours are used to show different temperatures.
Which colour on a thermogram shows where it is hottest?
White or yellow to red.
Which colour on a thermogram shows where it is coldest?
Black or purple to blue.
What is specific heat capacity?
The energy needed to raise the temperature of 1 kg of a substance by 1 degree.
What is specific latent heat?
The energy needed to change the state of 1 kg of a substance without it changing temprature.
If a substance has a high specific heat capacity, what does this tell you about how it heats up?
Substances with a high specific heat capacity take a lot of energy to heat up, so will heat up slowly.
If a substance has a high specific heat capacity, what does this tell you about the amount of energy it stores?
Substances with a high specific heat capacity take a lot of energy to heat up, so can store a lot of energy.
If a substance has a high specific heat capacity, what does this tell you about how it cools down?
Substances with a high specific heat capacity store a lot of energy so will cool down slowly.
Would you want a high or low specific heat capacity for a liquid used to fill a radiator? Why
You would want a high specific heat capacity for a liquid used to fill a radiator because it would store a lot of energy and cool down slowly.
What happens to the temperature of something as it changes state (melts, freezes, boils etc)?
Nothing, it stays the same while the substance changes state. E.g. Ice at zero degrees will melt to water at zero degrees.
What happens to the energy used to freeze something if the temperature doesn’t change?
Intermolecular bonds are made which releases energy, so the temperature stops falling and remains constant, until all the substance is frozen.
What happens to the energy used to melt something if the temperature doesn’t change?
The energy is used to break intermolecular bonds.
Name 5 ways you can reduce energy loss in your home.
Loft insulation, cavity wall insulation, double glazing, draught excluders, silver foil behind radiators.
Explain how conduction happens in solids.
Particle gain energy and vibrate more. These vibrations are passed on to the next particle, then the next and so on until the vibrations (heat energy) have passed along the solid.
Why are metals such good conductors of heat?
They have free electrons which can move between the metal ions and transfer heat energy quickly along the metal.
Why is water a bad conductor?
Water is a bad conductor because it is a liquid and in a liquid the particles are not held together very tightly, so the vibrations don’t get passed on to the next particle.
Explain how heat is transferred by convection in liquids and gases.
As the particles are heated they gain energy and move around more. This makes them spread out. The spread out areas (hot areas) are less dense than the cold areas and therefore lighter, so the hot liquid or gas rises. It is replaced by cold fluid which sinks. This sets up a convection current.
Is it true to say that ‘heat rises’?
No, heat is not a substance! Hot liquids or gases rise!
How is heat transferred by radiation?
Heat transferred by radiation in the form of infra-red waves. This is like light but a longer wavelength.
What sort of surfaces are the best absorbers of infra-red radiation?
Black matt surfaces absorb radiation the best, so will heat up more than white shiny surfaces.
What sort of surfaces are the best emitters of infra-red radiation?
Black matt surfaces emit radiation the best, so will cool down more than white shiny surfaces.
What is meant by ‘efficiency’?
A measurement of the useful energy output as a percentage of the total energy input. Eg. a Bulb that converts 50 J of energy into light out of 200 J of electricity siupplied would be 25% efficient.
What is a Sankey diagram?
A diagram that uses arrows to show energy transfer and efficiency.
What is ‘pay-back time’?
The time it takes for you to save money from insulation and pay back the cost of the insulation itsself.
E.g. draught excluders cost £100 and save you £25 a year.
Payback time = 4 years.
What are the two types of waves?
Transverse and longitudinal are the two different types of wave.
How would you define a transverse wave?
The movement of the particles is at right angles to the direction of the wave.
How would you define a longitudinal wave?
The movement of the particles is parallel to the direction of the wave.
Name a longitudinal wave
Sound is good example of a longitudinal wave.
What is frequency?
Frequency is the number of waves per second OR oscillations per second.
What is diffraction?
As waves move through gaps they spread out. The maximum diffraction happens when the gap is the same size as the wavelength of the wave.
Waves also diffract when they move past an object.
What is refraction?
As light moves from a less dense medium to a more dense medium the light bends towards the normal. This change of direction is called refraction.
What is the electromagnetic spectrum?
A family of waves: radio waves, microwaves, infrared waves, visible waves, ultraviolet waves, x rays and gamma rays.
Can you recall the e/m spectrum in order of decreasing frequency?
What is the law of reflection?
The angle of incidence = angle of reflection
What is a digital signal?
A signal that is either on or off i.e. 1 or a zero
What is an analogue signal?
A signal that can have any value within a range. An example would be sound.
What are the advantages of digital signals over analogue signals.
Both signals pick up noise, but on a digital signal the noise is not recognised when the signal is looked at. This can make digital signals clearer than analogue ones.
What is total internal reflection?
Total internal reflection is when light reflects at the boundary of two substances rather than refracting out.
When does total internal reflection happen?
It happens if they angle of incidence is greater than the critical angle.
What is the critical angle?
Trhe critical angle is the lowest angle of incidence at which total internal reflection can happen.
Give two examples the uses of total internal reflection.
Optical fibres and endoscopes.
What’s special about laser light?
Laser light is just one wavelength or frequency (monochromatic), doesn’t spread out much (has low divergence) and is in phase.
What does ‘coherent’ mean when talking about laser light?
Coherent means in phase and monochromatic
How does a laser read a CD?
The laser reflects from a series of pits and lands on the surface of the CD. The reflections are detected and produce a digital signal.
How does light travel down an optical fibre?
Light travels down an optical fibre in a series of total internal reflections.
Why are radio waves easier to pick up than microwave signals?
Radio waves diffract more arouind buildings and hills beacause they have a longer wavelength than microwaves.
What sort of waves do mobile phones transmit?
Mobile phones transmit and receive microwaves.
Why do some people think mobile phones are dangerous?
Some people think mobile phones are dangerous because microwaves can damage or kill living cells.
How can radio waves be sent round the Earth?
Radio waves can reflect off the ionosphere (the charged layer of the atmosphere) and reflect around the Earth.
Why is it a good idea to stir food at intervals during microwave cooking?
It’s a good idea to stir food to allow the cooler food in the centre to move to the outside where the microwaves can heat it up.
Why is it a good idea to let food stand for a while after mocrowave cooking?
Food is left to stand so that the he heat has time to reach he centre of the food by conduction or convection.
What are some uses of infra -red radiation?
Cooking
Remote controls
Passive Infra Red (PIR) detectors in burglar alarms and outside lights.
Night vision goggles.
How does a remote use infra red to send a signal?
The infra red wave carries information coded in the signal so it know the difference between each button on the remote control.
What does DAB stand for?
Digital Audio Broadcasting (digital radio)
What are the advantages of DAB
The advantages of DAB are that there is less interference and more stations can be carried.
What sort of waves are used to send signals via satellites?
Microwaves are used to send signals via satellites because they can penetrate the atmosphere.
What type of radiation does the ozone layer protect us from?
The ozone layer protects us from ultra-violet radiation.
What effect can ultra-violet radiation cause to the skin?
UV can cause sun-tan, sun burn or even skin cancer.
Why do people with darker skin have a lower risk of skin cancer?
Dark skin absorbs more ultra violet. This stops it penetrating deeper into the skin damaging the tissue below.
What are the two types of earthquake (seismic) waves?
The two types of earthquake (seismic) waves are P and S waves.
What are the key features of P waves?
The key features of P waves are:
Primary waves
Faster than S waves
Longitudinal
Can go through solids and liquids
What are the key features of P waves?
The key features of S waves are:
Secondary waves
Slower than P waves
Transverse
Can go through solids only
How do scientsist use earthquake waves to work out what the inside of the Earth is like?
S waves don’t travel through liquid, and leave a shadow zone which shows that the outer core must be made of liquid. Refraction also shows how the density inside the Earth changes.
What’s a seismometer?
A seismometer is a device for measuring seismic waves.
What’s a seismograph
A seismograph is the picture of vibrations caused by earthquake waves.
