Standard Grade Physics Summary Notes Health Physics Telecommunications Electricity
Health Physics Thermometers Sound Light and Sight Using EM Waves Ionising Radiation
Thermometers You should be able to: State thermometers need a property that changes with temperature and is easily measurable. Describe how a liquid in glass thermometer works. Describe the main differences between a clinical and ordinary thermometer. Describe how body temperature is measured using a clinical thermometer. Explain how body temperature is used in the diagnosis of illness.
Types of Thermometer • Thermometers have a property which is easy to measure and changes with temperature. Different thermometers have different properties. • Liquid in Glass – Volume of liquid changes • Rotary – Contains a bimetallic strip which bends • Digital – Some electrical property • Crystal strip – Colour change • Thermometers are carefully designed to measure specific things,
Clinical Thermometers • Clinical thermometers measure body temperature. They are different from normal thermometers in a number of ways: • Small Range The range only goes from 32ºC - 42 ºC (outside this range a person is dead) • Small Divisions Allows more accurate readings • Kink in the glass Stops mercury until it is reset • Toughened Glass Safety feature • White background Make it easier to read • Lens-like glass Make it easier to read
Measuring Body Temperature • Clinical thermometers can be used to measure body temperature using the following steps. • Disinfect the thermometer • Shake the thermometer • Place the thermometer under the patient's tongue • Leave the thermometer for a few minutes • Remove the thermometer and read the scale • Normal Body Temperature is 37 ºC • Above this you are too hot – Fever • Below this you are too cold - Hypothermia Back to Health Menu
Sound You should be able to: State what sound energy can and cannot travel through. Explain how a stethoscope can aid to hearing. Give one example of a use for ultrasound in medicine. Name sounds too high for humans to hear. Give examples of sound levels of some everyday sounds. State that excessive noise can damage hearing. Give two examples of noise pollution. Explain a use for ultrasound in medicine.
Sound Waves • Sounds are vibrations – the number of vibrations every second is called the frequency. • Sounds need to travel through matter. • Sounds can travel through solids, liquids and gases • Sounds can’t travel through a vacuum (like space).
Stethoscope • Stethoscopes are used in medicine to listen to sound made by the body. • The stethoscope has ear-pieces, tubing and two bells. • The open bell is for listening to low frequency sounds from the heart • The closed bell is for listening to high frequency sounds from the lungs
Ultrasound • Humans can hear sounds of certain frequencies. • The range of human hearing is 20-20,000 Hz. • Sounds greater than this are called ultrasounds • Ultrasounds have many uses in medicine, from shattering kidney stones to scanning unborn babies. • Ultrasound is very safe and will not damage cells unlike X-rays.
Sounds can be loud or quiet. Loudness of a sound is is measured in decibels (dB) Loud sounds (over 100dB) can damage hearing. People who work with loud noises wear protection to prevent damage. Sound Levels Unwanted sounds are called noise pollution – for example traffic or loud music Back to Health Menu
Light and Sight You should be able to: Explain what is meant by refraction. Explain how an image is formed in the eye Draw ray diagram of an object and image Describe the affects of long and short sightedness. State how lens can correct eye defects. Describe how to measure the focal length of a lens Carryout calculations with power and focal length Describe how light travels in a Fibre Optic Explain how fibre optics are used in an endoscope Explain the meaning of a “cold-light source”
Refraction is the bending of light as it passes from one material to another. The normal is an imaginary line at 90° to the boundary. The angle between the ray and normal is small in denser materials. Refraction You must be able to draw this.
The Eye • Light is focussed in the eye by the lens and cornea. • An image is produced on the retina and information is carried to the brain by the optic nerve. The blind spot is where the optic nerve joins the retina.
object f f lens Ray Diagrams 4 Steps to drawing a ray diagram: • Draw a line from the top of your object to the lens • Continue this line through the focal point. • Draw a line from the top of the object through the middle of the lens. • Draw in your object to where the rays cross
Long sighted people can only see long distances clearly. Light focuses long of the retina Eye Defects Short sighted people can only See short distances clearly. Light focuses short of the retina
Convex Lens: Converges Light Corrects for Long-sightedness Lenses Lens are transparent objects that bend light Convex Lens: Diverges Light Corrects for Short-sightedness
Measuring Focal Length • Set up the equipment as shown and with light from a distance source (e.g. the sun) focus an image of a sheet of paper. • Measure the distance form the lens to the image in meters to find your focal length
Power = 1 focal length Power = 1 = 1 = 5D f 0.2 Power and Focal Length • The power of a lens is measured in Dioptres (D) • Find it using the equation: • Example: A lens has a focal length of 20 cm • P = ? • f = 0.2 m
Fibre Optics • Fibre optics are very thin strands of glass. • Light travels along them at 2x108 m/s by total internal reflection. • = the normal – at 90º to the boundary
Endoscopes • An endoscope is an instrument that Doctors can use to look inside your body. It has two Optical fibres. • One fibre provides a “cold light source”, allowing light (but not heat) to travel down and light up the area, the other fibre allows light to travel up to the Doctor’s eye. Back to Health Menu
Using EM waves You should be able to: Describe one use of the laser in medicine Describe one use of X-rays in medicine State how X-rays can be detected Describe the use of infrared and ultraviolet radiation in medicine State that too much ultraviolet radiation may cause skin cancer Describe the advantages of computer aided tomography
Electromagnetic Waves The electromagnetic spectrum is a collection of light waves that have different frequencies. Different frequencies of light have different uses in medicine. Visible light: RichardOfYorkGaveBattleInVain. Any light with a frequency higher than violet light waves or lower than red light waves are invisible to the naked eye.
Lasers • A laser is a very concentrated form of light. Lasers can provide either heat or light to treat parents. • Examples: • Laser Eye surgery • Reattaching Retina • Bloodless scalpel
Infra Red Infra-red (I.R.) Radiation is low frequency light waves. Tumours tend to give off heat (infra-red) , which can be detected by an I.R. camera. Infra-red radiation is used to treat muscle strains.
UV • Ultra Violet radiation is a high frequency light wave. It can be used to treat skin problems and jaundice. • UV light is also used to sterilise medical instruments. • Overexposure has been shown to increase the risk of skin cancer.
X-rays X-Rays are very high frequency light waves which pass through soft tissue but not bone. This means that if X-rays are sent in to the body, they will pass through skin and muscle but will be reflected by bone.
CAT Scan C.A.T. (Computer Assisted Tomography) scans make use of X-Rays. The patient is placed in to a tube and X-Rays are emitted in to the patient from many different positions and at many different trajectories. This results in a 3D image of the patient which also shows tissue.
Ionising Radiation You should be able to: State the effect of nuclear radiation on living cells Explain how radiation can be used in medicine Describe the range and absorption of α, β and γ Describe a model of the atom and ionisation Give one effect of radiation on non-living things State the unit of radiation activity Describe how to measure activity Describe the activity of a source over time and calculate half-life State the unit used to measure dose equivalent”
Radiation and Cells • Nuclear radiation can mutate and kill living cells. • Because of this they are used in medicine to: • Sterilise instruments (by killing bacteria) • Kill cancer cells • Radiation can also be used as a tracer – a picture of the body can be taken with a gamma camera to show if an organ is working correctly.
Ionising Radiation • There are three main types of nuclear radiation: • alpha(α) – a helium nucleus (2 protons, 2 neutrons) • beta(β) – a high energy electron • Gamma (γ) – part of the EM spectrum Alpha is the most ionising, gamma is the least ionising
Atoms • Atoms are made up of: • Protons (+ve) • Neutrons • Electrons (-ve) • Atoms have no overall charge as the no. of protons is cancelled out by the equal number of neutrons. • Ionisation is when an electron is lost of gained by an atom and it becomes charged. Alpha radiation causes the most ionisation.
Detecting Radiation • Ionisations caused by radiation can be measured using a Geiger- Müller tube. The tube contains a gas which conducts a pulse of electricity every time an atom is ionised. • Radiation also turns photographic • film white. Radiation badges are • worn by people who have to work • with radiation – the amount that • a piece of film has fogged shows • the exposure to radiation.
Measuring Radioactivity • The activity of a radioactive source is the number of nuclear decays per second measured in Becquerels, Bq. • Activity (Bq) = Number of decays • time (s) • To calculate the activity of a source: • Find the background activity • Find the activity next to the source. • Subtract the background activity form your results
Half-life • Over time the activity of a source decreases. • The half-life of a source is the time taken for the activity to decrease to half its original value. • You should be able to calculate • half-life from a graph and • from information about the • Source.
Equivalent Dose • The biological effect of radiation is called the equivalent dose it has the units Sieverts (Sv). • It depends on: • The type of tissue exposed • The type of ionising Radiation • The energy of ionising radiation • Alpha has greater effect than beta or gamma. • The longer you are near radiation the greater the risk. Back to Health Menu
Telecommunications Communication with Waves Communication with Cables Radio and Television Transmission of Waves
Communication with Waves You should be able to: Compare the speed of sound and light with examples. Describe to measure the speed of sound in a lab. Use the following terms correctly : wave, frequency, wavelength, speed, energy transfer and amplitude Use the equation speed = distance/time. Use the equation speed = frequency x wavelength. Explain the equivalence of frequency x wavelength and distance / time.
Speed of Sound and Light • The speed of light is about a million times faster than the speed of sound • The speed of sound is about 340 m/s • The speed of light is 300 000 000 m/s • This is obvious during a lightning storm. • You see the lightning then you hear the thunder even though they are produced simultaneously (at the same time)!
Measuring the Speed of Sound • Set up the equipment as shown • Make a sharp noise at X • As the sound passes mic 1 thetimer starts, as it passes mic 2the timer stops. • Use the equation: Speed = distance/time
Wave Properties You should know the following terms Amplitude (A) - height of wave Wavelength () - length of wave Wave-speed (v) - speed of wave Frequency – (f) - waves per second Waves transfer energy. The greater the energy the greater the amplitude.
Frequency of Waves Frequency = no. of waves time Example: 240 waves pass a point in 1 minute. f = ? n = 240 t = 1 minute = 60 s f = n = 240 = 4 Hz t 60 f = frequency (Hz)v = speed (m/s)t = time (s)
Speed, distance and time speed = distance time Example: A wave travels 120 m in 1 minute. v = ? d = 120 t = 1 minute = 60 s v = d = 120 = 2 m/s t 60 d = distance (m)v = speed (m/s)t = time (s)
Speed, frequency and wavelength speed =frequency x wavelength Example: Find the speed of a 20 m wave and a frequency of 30 Hz. λ = 20 m v = ? f = 30 Hz Speed = f x λ = 20 x 30 = 600 m/s λ = wavelength (m)f = frequency (Hz)v = speed (m/s)
Wave Equations Speed = frequency x wavelength = distance time f = frequency (Hz) n = no. of wavest = time (s) f = frequency (Hz)v = speed (m/s)t = time (s) d = distance (m)v = speed (m/s)t = time (s) Back to Telecoms Menu
Communication with Cables You should be able to: Describe a method of communication using wires. Explain how a telephone sends and receives signals. State that electrical signals travel along wires Describe how signal patterns change with volume/freq. Explain the term reflection Explain the term total internal reflection State what is meant by an optical fibre. Describe how signals are transmitted in a fibre optic State advantages/disadvantages of a fibre optics Carryout calculations involving v = d/t for fibre optics.
Communicating with cables Messages can travel through air or through cables. Messages which travel through cables are usually more private and faster than messages which travel through air. Examples include: The telephone (landline) Broadband Internet Morse code
The Telephone • Telegraphs and telephones use wires to send messages. • Telephones have a receiver and transmitter. • The earpiece contains a loudspeaker. • (electrical energy sound energy) • The mouthpiece contains a microphone. • (sound energy electrical energy) • Telephones transmit electrical signal .
Low and Quiet High and Quiet Low and Loud High and Loud Sounds on an Oscilloscope