Physics Unit 1 Key Points.

Physics Unit 1 Key Points

Topic 1: Visible Light and the Solar System
P1.1 – The Solar System P1.2 – Refracting telescopes P1.3 – Lenses: PCA P1.4 – Reflecting telescopes P1.5 – Waves

Geocentric Ptolemy Solar system goes round Earth Heliocentric Copernicus and Galileo Solar system goes round Sun Galileo used telescope to see Jupiter’s moons, this was evidence for heliocentric model

Lenses:

Lenses: Options: Object beyond 2F: image inverted, made smaller, appears between F and 2F (other side of lens), real image produced Object at 2F: image inverted, same size, appears at 2F, real image Object between 2F and F: image inverted, made bigger, appears beyond 2F, real image Object at F: no image formed Object between F and lens: image right way up, image made bigger, virtual image formed

Telescopes: You must be able to compare and contrast these and label diagrams

Waves: Wavelength Frequency Amplitude Wave equation: v = wave speed (metre per second, m/s) f = frequency (hertz, Hz) λ = wavelength (metre, m)

Topic 2: The electromagnetic spectrum
P1.6 – Beyond the visible P1.7 – The electromagnetic spectrum P1.8 – Electromagnetic dangers P1.9 – Using electromagnetic radiation P1.10 – Ionising radiation

frequency type of electromagnetic radiation wavelength highest gamma radiation shortest X-rays ultraviolet visible light infrared microwaves lowest radio waves longest

Herschel Discovered infrared Ritter Discovered ultraviolet

Dangers: IR – heat, causing burns UV – damage to eyes, skin cancer X-rays – cancer (medical doses are carefully monitored) Gamma rays – cancer (again, medical doses monitored) Uses: Various – read up on them! Ionising radiation: Radiation with energy levels powerful enough to remove electrons from atoms to form ions Radiation that doesn’t have enough energy to do this is non-ionising High energy X-rays and gamma rays are ionising So is radiation from radioactive materials This can be alpha (α), beta (β) or gamma (γ) radiation.

Topic 3: Waves and the Universe
P1.11 – The Universe P1.12 – Spectrometers: PCA P1.13 – Exploring the Universe P1.14 – Alien Life? P1.15 – Life-cycles of stars P1.16 – Theories about the Universe P1.17 – Red shift

Planet Comet Asteroid Moon Star Star cluster Galaxy Nebula (nebulae) Distances: Understand the scale of the Universe Telescopes are used to observe all regions of the EM spectrum Earth based telescopes v space based Advantages and disadvantages of each

Each colour in a rainbow corresponds to a different wavelength of electromagnetic spectrum: Spectrometers are used to measure the spectrum from a light source such as a star

Red-shift: Our sun contains helium. We know this because there are black lines in the spectrum of the light from the sun, where helium has absorbed light. These lines form the absorption spectrum for helium. When we look at the spectrum of a distant star, the absorption spectrum is there, but the pattern of lines has moved towards the red end of the spectrum, as you can see here. This is called red-shift, a change in frequency of the position of the lines. Astronomers have found that the further from us a star is the more its light is red-shifted. This tells us that distant galaxies are moving away from us, and that the further a galaxy is the faster it is moving away. Since we cannot assume that we have a special place in the universe this is evidence for a generally expanding universe. It suggests that everything is moving away from everything else. The Big Bang Theory says that this expansion started billions of years ago with an explosion.

Alien Life: Space probes Landers Rovers SETI

Star formation: Stars form from massive clouds of dust and gas in space Gravity pulls the dust and gas together As the gas falls together, it gets hot. A star forms when it is hot enough for nuclear reactions to start. This releases energy, and keeps the star hot. The outward pressure from the expanding hot gases is balanced by the force of the star's gravity. Our sun is at this stable phase in its life. Gravity pulls smaller amounts of dust and gas together, which form planets in orbit around the star

Big Bang Theory Steady State Theory Cosmic background radiation

Topic 4: Waves and the Earth
P1.18 – Infrasound P1.19 – Ultrasound P1.20 – Seismic waves P1.21 – Earthquakes: PCA P1.22 – Detecting earthquakes

Sound waves: Audible range between 20Hz and 20 000Hz (or 20kHz) Sounds waves with frequency <20Hz are called infrasound Sound waves with frequency >20 000Hz are called ultrasound

Sound waves: These diagrams show snapshots from oscilloscope traces of three sounds. Diagrams 1 and 2 show two sounds with the same frequency but different amplitude (the height of the trace). The trace on 1 comes from a sound with a smaller amplitude than on 2. Sound 1 is quieter than sound 2. Diagrams 2 and 3 show two sounds with the same amplitude but different frequencies. The faster the vibrations, the higher the frequency and the more highly pitched the sound. The trace on 3 comes from a sound with a higher frequency than the one on 2. So sounds 2 and 3 are the same volume (loudness), but 3 is higher pitched.

Infrasound: Cannot be heard by humans <20Hz frequency Used by some animals to communicate, eg elephants, giraffes, whales Produced by some natural events such as volcanic eruptions Can be used by scientists to help track meteorites

Ultrasound: Cannot be heard by humans >20 000Hz in frequency (=20kHz) Medical scanning (eg foetal scan) Ultrasound is sent into the patient's body. Some of the ultrasound is reflected at each boundary between different tissues or organs. The depth of each layer is calculated using the time taken for each reflected wave to return. Sonar Speed = distance ÷ time Don’t forget: depth = distance ÷ 2 v = wave speed (metre per second, m/s) x = distance (metre, m) t = time(second, s)

Seismic waves: P waves and S waves

Seismic waves

Seismic waves:

Topic 5: Generation and transmission of electricity
P1.23 – Renewable resources for electricity P1.24 – Non-renewable resources P1.25 – Investigating generators: PCA P1.26 – Generating electricity P1.27 – Transmitting electricity P1.28 – Paying for electricity P1.29 – Power consumption: PCA P1.30 – Reducing energy use

Renewable energy sources: Solar cells Hydroelectricity Wind turbines Geothermal energy Tidal power Wave power Biomass Make sure you can compare and contrast each of these

Non-renewable resources: Fossil fuels Oil Gas Coal Nuclear Make sure you can compare and contrast each of these Make sure you can compare and contrast renewable and non-renewable resources

Generating Electricity: Electromagnetic induction Simple generator size of current increased by Using a coil of wire or putting more turns on the coil Using an iron core inside the coil Using stronger magnets Moving the coil faster

Power generation: Water is turned into steam in the boilers The steam drives the turbines The turbines spin the generators, which produce the electricity The electricity goes to the transformers to produce the correct voltage The energy needed to boil the water comes from fossil fuels or nuclear fuels. Renewable energy resources such as wind and wave power may drive the generators directly.

Transmitting electricity:

Transformers: Step up transformers increase the voltage Step down transformers decrease the voltage Structure of a transformer: Transformer equation: Vs = voltage in the secondary winding (volt, V) Vp = voltage in the primary winding (volt, V) Ns = number of turns in the secondary winding Np = number of turns in the primary winding.

Various formulae: Electrical power, current and potential difference Power, energy and time Cost of electricity cost = power (kilowatts, kW) x time (hour, h) x cost of 1 kilowatt-hour (kW h) P = power (watt, W) I = current (ampere or amp, A) V = potential difference (volt, V) P = power (watt, W) E = energy used (joule, J) t = time taken (second, s) Care with units!

Reducing energy use: Be able to talk about methods of reducing energy use Solar panels Loft insulation Cavity wall insulation Draught proofing Insulation on hot water tank Using other appliance to do the job (microwave instead of oven / low energy light bulbs)

Payback time: Cost-efficiency: The most cost-efficient method saves the most money compared to its cost The most cost-efficient method is the one with the shortest payback time

Topic 6: Energy and the future
P1.31 – Energy transfers P1.32 – Efficiency P1.33 – Heat radiation: PCA P1.34 – The Earth’s temperature

Energy transfers Be able to list different types of energy and talk about how machines change energy from one type to another Thermal (heat); light; electrical; kinetic; sound; chemical potential; nuclear potential; gravitational potential; elastic potential Law of conservation of energy Energy cannot be created or destroyed It can only be transferred from one place to another or transformed from one form to another

Energy conversion diagrams (Sankey diagrams):

Efficiency:

Efficiency: How good a device is at converting energy into other useful forms of energy is call its efficiency

Heat radiation: Different colours absorb and radiate heat better than others Matt black is the best absorber and radiator Glossy silver is the worst absorber and radiator If an object is to stay at the same temperature then heat energy in must be equal to heat energy out

Greenhouse effect: Greenhouse gases cause the Earth’s temperature to warm up These gases are carbon dioxide, methane and others The Sun’s rays enter the Earth’s atmosphere Heat is reflected back from the Earth’s surface Heat is absorbed by greenhouse gases, such as carbon dioxide, and as a result becomes trapped in the Earth’s atmosphere The Earth becomes hotter as a result

Physics Unit 1 Key Points.

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Physics Unit 1 Key Points.

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