National 4 & 5 Physics Portree High School



Waves and Radiation 2 – Summary NotesWave Parameters – revisited 2952750278130When discussing a wave, we need to know about AMPLITUDE, FREQUENCY, WAVELENGTH, PERIOD, SPEED.FREQUENCY (F) – This is the number of waves produced each second, measured in Hertz (Hz). ‘C ‘on the piano has a frequency of 260 Hz, that is 260 waves each second. AMPLITUDE (A) – This is the distance in metres from the CENTRE LINE to the CREST or TROUGH.WAVELENGTH (?) – This is the distance of one complete wave measured in metres. It can be from CREST to CREST, TROUGH to TROUGH, or CENTRE to CENTRE. The symbol ? (lambda) is used to represent wavelength.PERIOD (T) – This is the TIME it takes one wave to pass a point, measured in seconds (s). If you know what the FREQUENCY of a wave is, you can work out the PERIOD using the formula T = 1/F. For example if a wave has a frequency of 100 Hz, the period, T = 1/100 = 0.01s.SPEED (v) – The speed of a wave can be calculated by knowing the DISTANCE the wave travels in a given TIME. Speed is measured in metres per second (ms-1). Speed , v = d/t.4257675189230The Wave Equation????v/ff = v/?This equation links the SPEED, FREQUENCY and WAVELENGTH of a wave.Speed = frequency x wavelengthV = f x ??Example:What is the speed of a wave of frequency 50 Hz and wavelength 2.5m?4257675163830V = ?f = 50 Hzv = f x ? = 50 x 2.5 = 125 ms-1? = 2.5mYour well known favourite equation for speed, d = v x t can also be used to solve wave problems.1390650-90170Diffraction 19050144780-4295775222250All waves DIFFRACT.Diffraction is when waves ‘bend’ round an object or through an opening in their path.LONG WAVELENGTHS diffract more than SHORT wavelengths.356235045085-28575321310-2618740292735Diffraction of laser light round a pin headWater waves diffracting between two islands350520069850Light diffracting through cloudsPractical Applications of Diffraction19050278130Using Diffraction to Split up White lightWhite light can be split up into the colours of the rainbow by using a DIFFRACTION GRATING.5334006350-38100256540 Using Diffraction to Measure the Wavelength of LightStudents follow these instructions. a Hold a metre rule straight out in front of you towards the lamp, with the near end of the rule at your face. Hold the diffraction grating against the near end of the metre rule and look at the lamp through it. b Ask your partner to place another metre rule, at 90° to your metre rule at its far end (see the sketch). c Your partner should hold a pencil vertically above their metre rule and move it along until you see it in the green region of your bright spectrum. Note the distance, y, along your partner's ruler from the pencil to the far end of your ruler. d When you have made your observation, record it and change places with your partner so that he or she can take their turn. e Divide your measurement y by the length of your ruler, 100 cm. This gives you tan X, where X is the angle between the line of direct white light and the light to the green in the spectrum marked by the pencil. From tan X, use your calculator to find the angle X, and from this find sin X. f Use the formula wavelength = d x sin X to calculate the wavelength of green light. You will need the value of d, spacing, i.e. distance between slits in your diffraction grating.Diffraction GratingValue of d to be used in formula15000 lines per inch1.67 x 10-680 lines/mm1.25 x 10-5Use of Diffraction – HOLOGRAMS2476501154430Holography is a technique that allows the light scattered from an object to be recorded and later reconstructed so that when you look at the hologram, an image of the object will be seen even when the object is no longer present. The image changes as the position and orientation of the viewer changes in exactly the same way as if the object were still present, thus making the image appear three-dimensional.IBM recon by 2015 we will all be able to use our smart phones to make mobile ‘hologram’ calls.Electromagnetic Spectrum247650-1905All members of the Electromagnetic spectrum travel at the speed of light (3 x 108ms-1).247650314325Medical Uses of the Electromagnetic Spectrum:Other uses of the Electromagnetic Spectrum:2476500445770057150Hazards Associated with the Electromagnetic RadiationsAlmost all the radiations that make up the Electromagnetic Spectrum are classed as ‘non-ionising’. Later, we will explore a family of radiations that are ‘ionising’.133350223520Ultraviolet (UV) RadiationCauses sunburn, premature skin ageing, wrinkles, skin cancer and cataracts. Precautions include covering up in the sun, use of sun lotion, eye protection.465772580645Infrared (IR) RadiationExposure to high intensity IR sources may cause skin burns. Stay away from hot objects!Radio-frequency and Microwave Radiation3286125473075May cause cataracts, sterility, and possibly cancer. Devices that emit these types of radiation should be properly shielded to avoid radiation leakage.Microwave ovens also have a safety feature that switches off the oven if you try and open the door when the oven is switched on – why do you think ovens have been made this way?219075253365Relationship Between Frequency and Energy Associated with a form of Radiationh = Plank’s Constant (6.63 x 10-34 JS)E = Energy in each photon of radiation (J)f = frequency of radiation (Hz)This can be described by the equation E = h x f4203700-342900Ionising (Nuclear) Radiation247650621030Ionising (or nuclear) radiation is radiation that can cause ionisation of living cells.Natural Sources of Ionising RadiationIonising radiation occurs naturally and is all around us. This is known as background radiation as comes from the following sources;Rocks (granite).Radon gas.Cosmic rays from space.Naturally occurring Potassium in our bodies.Our bodies have adapted to cope with this background radiation, and under normal conditions, it is harmless.ActivityThe ACTIVITY of a radioactive source is measured in BEQUERELS (Bq).One radioactive particle produced each second is an activity of 1 Bq.We can use the formula A = N/t to calculate the activity of a source.A = Activity in BqN = Number of decays in time t secondsExample:Calculate the activity of a source if there are 12000 decays in 5 minutes.A = ?N = 12000t = 5 mins = 5 x 60 = 300 sA = N/t = 12000/300 = 40 BqApplications of Ionising RadiationIonizing radiation has many uses, including killing cancerous cells and power generation. However, although ionizing radiation has many applications, overuse can be hazardous to human health. For example, at one time, assistants in shoe shops used X-rays to check a child's shoe size, but this practice was halted when it was discovered that ionizing radiation is dangerous.-552450889635Nuclear Power. The energy released as a result of NUCLEAR FISSION (see later) can be used to turn water into steam, which in turn can be used to turn a turbine that is linked to a generator. The generator produces electricity as it turns. Vast quantities of energy are potentially available from small quantities of radioactive fuel. 107632566675However, there are some major problems. Generation of electricity in this way causes harmful ionising radiation to be produced and the creation of dangerous radioactive waste that takes decades to decay to a safe state. Under normal safe operating conditions nuclear power plants are safe to be around, but they have, in the past, resulted in some very high profile accidents.4095750-266700 Non-destructive testing. Ionising radiation (x-rays) can be used to penetrate solid objects to find if there are any cracks or failures. For example, aircraft wings and oil rig legs. 4400550400050 Level indicators. A source and detector are placed at either side of a container. The level of radiation received by the detector can be used to determine the correct level of fluid in the container. Thickness Gauges. Similar to above. The level of radiation received is an indication of the thickness of material placed between the source and detector. 142875164465Smoke Detectors. Most smoke detectors have a small radioactive source that produces ionisation of the air around it. These ions help close an electrical circuit and a current flows. If smoke enters the detector, the ions are prevented from flowing, this disrupts the current and the alarm is made to sound. Sterilisation of Medical Tools and Equipment. Tools are placed in a container and then exposed to ionising radiation that kills off any bacteria.4162425-238125Radioactive Tracers. A radioactive substance can be injected into the blood stream. By taking pictures with special cameras or by taking blood samples at different points in the body, many thinks can be found out about a patient’s condition. Radiation Therapy. Cancerous tumours within the body are targeted by beams of ionising radiation. The cancerous tissue is killed off by the radiation.176212516510The nature of Alpha, Beta and Gamma RadiationType of RadiationWhat stopped byHow far in airWhat is it?Alpha, ?PaperA few cmHelium nucleusBeta, ?Several cm AlA few 10s of cmElectronGamma, ?Lead/ concreteFor everElectromagnetic waveEquivalent DoseEquivalent Dose is a quantity that gives us an idea of the risk of biological harm due to ionising radiation. It is measured in Sieverts (Sv).Comparison of Equivalent DoseAverage exposure due to watching colour TV = 0.000002SvAircrew flying for many hours at high altitude = 0.001SvAnnual exposure due to background radiation = 0.0037 SvRadiation induced cancers from nuclear accidents = 0.2 Sv4686300170180Half life -171450535940This is the time it takes the activity of a radioactive source to fall to half of its original value.Half Life QuestionsExample 1:54292543815Calculate the half life of a radioactive source of the activity falls from 4800 Bq to 600 Bq in 18 days.It takes 3 half lives for the activity to fall from 4800 to 600 Bq.3 half lives is 18 days, therefore 1 half life is 18/3 = 6 daysExample 2:542925386715The half life of a source is 30 s. What fraction of the activity will remain after 3 mins has elapsed?3 mins is 6 half livesAfter 6 half lives, the activity falls to 1/64th of its original value.Example 3:762000705485At 7am on 12 May, a hospital receives a radioactive sample with an activity of 1000 Bq. The material has a half life of 2 hours, and can only be used on a patient when the activity falls to 125 Bq. Calculate at what time of day the sample will be safe to use.From 1000 to 125, there are 3 half lives:Three half lives = 3 x 2 = 6 hours.7am + 6 hours = 1pm in the afternoon4467225-156845Nuclear ReactionsThere are two forms of reaction that we need to know about:FissionFusionBecause these words look quite alike, you really need to get the spelling right!28575330200Nuclear FissionThis is the process that takes place in our nuclear power stations. One large radioactive nucleus splits into two smaller nuclei, and energy is given off. 3657600343535Nuclear fission is an example of a CHAIN REACTION. Each neutrons produced by the first reaction can go on and cause other separate reactions which in turn produce their own neutrons...Energy is given off every time a nucleus splits.Nuclear Fusion3132455142240This is how energy is produced in the sun. Fusion is when two small nuclei combine to give one large nucleus, releasing energy in the process.447675130175 ................
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