Presentation on theme: "Atomic structure refresher….."— Presentation transcript:
1 Atomic structure refresher….. An atom contains: protons, neutrons and what other particle?....A proton has a positive charge? (true or false)In the nucleus are protons and which other particle?....Which particle is not in the nucleus?....The ATOMIC number means the number of what?....The MASS number means the number of what?.... Plus what?....An isotope of an atom has the same number of protons, but different number of what?....An ion (charged atom) is formed when by the addition or removal of what?....What particle is modelled to exist only at fixed distances from the nucleus according to the corresponding energy level?...
2 Physics of Radiography Electricity, EM and waveparticle duality
3 By the end of the session you should be able to: Explain the difference in how energy is transferred with transverse and longitudinal wavesGive one example of each type of wavePoint out on a wave diagram what the amplitude/wavelength/crest/trough areShow how a wave would look if it’s frequency or amplitude were changedDescribe wave particle dualityUnderstand how electricity is generated
4 How does energy change across the electromagnetic spectrum How does energy change across the electromagnetic spectrum? Which is more energetic microwave or x-rays?
5 WAVESWaves transfer energy & information but without transferring matterThe energy is transferred by oscillations in the material which the wave is travelling thoughA wave transfers energy through a medium without the medium itself having to move.The energy is transferred by disturbances (oscillations) in the medium (material) through which the transfer is occurring.There are many different kinds of wavesElectromagnetic waves pass through a vacuum & do not need to be carried by a substance.Light, infra red & microwaves all make things warm up. X-rays & gamma rays can cause ionisation and damage to cells, which also show that they carry energy.Loud sounds make things vibrate or move. Even the quietest sound move your eardrumWaves on the sea can toss big boats around and can generate electricity.Waves also transfer information, as well as energy. E.g. TV, radio, speech, fibre optics etc5
6 CLASSIFYING WAVES Mechanical Waves Waves that pass though a material are vibrations of that materialeg. Sound waves, seismic waves, strings2) Electromagnetic WavesVibrating electrical or magnetic fields through space (no material needed)eg electromagnetic spectrum
7 TYPES OF WAVES 1. Longitudinal Waves E C DirectionofTravelECOscillations occur parallel to direction of travelSound waves – a vibrating surface in contact with air.The surface pushes air molecules away which push adjacent air moleculesDepending on the motion of the medium compared to the movement of the wave, waves are classified as either transverse or longitudinal.Transverse waves have sideways vibration. Vibrations are at 90* to the direction of travel of the wave.Most waves are transverse.Longitudinal waves have vibrations along the same direction as the wave is travelling.which push adjacent air molecules which push adjacent air molecules which push adjacent air molecules which push adjacent air molecules which push adjacent air molecules which push adjacent air molecules which push adjacent air molecules which push adjacent air molecules which push adjacent air molecules which push adjacent air molecules which push adjacent air molecules which push adjacent air molecules which push adjacent air molecules which push adjacent air molecules which push adjacent air molecules…….Compression (C)Expansion (E)7
9 TYPES OF WAVES 2. Transverse Wave DirectionofTravelOscillations at right angles (90o) perpendicular to direction of travelElectromagnetic waves – radiowaves, X-rays, microwaves, visible light etcWaves on a string or wire – plucking a guitar stringDepending on the motion of the medium compared to the movement of the wave, waves are classified as either transverse or longitudinal.Transverse waves have sideways vibration. Vibrations are at 90* to the direction of travel of the wave.Most waves are transverse.Longitudinal waves have vibrations along the same direction as the wave is travelling.9
10 Parts of a WaveWavelengthPeakAmplitudeATroughx1 complete wave
11 Key TermsDisplacement (s) – the distance from the equilibrium positionWavelength (l) – the distance between identical points in a wave trainAmplitude (A) – maximum displacement of a particle (peak or trough max.)Period (T) – the time taken for 1 complete wave to pass a pointFrequency (f) – number of cycles per second. Measured in Hertz (Hz).
12 Amplitude and Frequency Low amplitude, low frequency:Low amplitude, high frequency:High amplitude, low frequency:High amplitude, high frequency:
13 WAVE SPEEDDTSWe know the relationship between distance, speed and time.Speed = Distance / TimeTherefore…Wave Speed = Wavelength / PeriodV = λ / TBut we know that T = 1/fSo we can substitute….
14 Wave speed (v) = frequency (f) x wavelength () The Wave Equationrelates the speed of the wave to its frequency and wavelengthWave speed (v) = frequency (f) x wavelength ()m/s Hz mVf
15 Speed (m/s) = wavelength (m) x frequency (Hz) Let’s try a few…An ocean wave has a wavelength of 1.5m. There are 2 of these waves hitting the shore each second. What speed is the wave travelling at?Wavelength = 1.5m Frequency = 2HzSpeed = 1.5m x 2Hz = 3m/sWhat speed would a wave be travelling if it had a wavelength of 4m and a frequency of 3Hz?Wavelength = 4m Frequency = 3HzSpeed = 4m x 3Hz = 12m/s
16 WAVE PROPERTIES 1. Reflection Waves will bounce off a surface under certain conditionseg the surface must be shiny for electromagnetic wavesReflective surfaceAll waves can be ReflectedIncident RayReflected Ray16
17 Angle of Incidence = Angle of Reflection WAVE PROPERTIESAngle of Incidence = Angle of ReflectionAngle of IncidenceNormalWhen waves are reflected from a flat surface, the Angle of Incidence (i) = the Angle of Reflection (r)Angle of Reflection17
18 WAVE PROPERTIES 2. Refraction Air Glass Block Normal Normal Waves cross a boundary causing a change in speed and consequently wavelengthDepends on the refractive index of different substancesNormalAll waves can be Refracted.Refraction is a change of direction due to a change of speed.The example I used involves light rays hitting a glass block. Glass is a medium which is more dense than air. so the light will travel more slowly within the glass block than it would do in air. As the light ray crosses the boundary from one medium to another, it bends.AirGlass BlockNormal18
20 WAVE PROPERTIES 3. Diffraction Occurs when waves pass through a gap or around an object of roughly the same size or smaller than their wavelength.Large gap - the middle parts of the waves go straight through the gap, with a slight curving at the edges of the waves.Small gap - if the gap is smaller than the wavelength of the waves, the waves fan out in circles.Diffraction occurs when waves pass through a gap or around an object of roughly the same size or smaller than their wavelength.When parallel water waves move towards a large gap, the middle parts of the waves go straight through the gap, with a slight curving at the edges of the waves.If however, the gap is smaller than the wavelength of the waves, the waves fan out in circles from the gap. The gap seems to act as a vibrating source and waves spread out from the gap.Diffraction provides evidence for the wave nature of water waves, sound waves & light.A good example of Diffraction of sound waves occur when you can hear people talking, out of sight, on the other side of a doorway. When the sound waves reach the doorway, they spread out and become diffracted around the door way.20
21 INTERFERENCE1. Constructive Interference - when the crests (or troughs) of two waves coincide, they combine to create an amplified wave.All waves can be ReflectedThe two waves are in phase with each other – there is zero phase difference between them.21
22 INTERFERENCE2. Destructive Interference - where the crests of one wave are aligned with the troughs of another, they cancel each other out.All waves can be ReflectedThe waves are out of phase (or in antiphase) with each other – they are half a cycle different from each other.22
30 To observe the photoelectric effect, you create a vacuum chamber with the photoconductive metal at one end and a collector at the other. When a light shines on the metal, the electrons are released and move through the vacuum toward the collector. This creates a current in the wires connecting the two ends, which can be measured with an ammeter.When electromagnetic radiation hits a metallic surface, the surface can emit electrons (called photoelectrons) An electric current is a flow of electric charge around a circuit.
32 Definitions: Energy in the form of transverse magnetic and electric waves. In a vacuum, these waves travel at the speed of light. Electromagnetic radiation:Photon:a quantum of electromagnetic radiation, usually considered as an elementary particle that has zero mass and chargeWave-Particle duality:Electromagnetic radiation exhibit wave like and particle like properties
33 How are energies and frequency related? Using the formulaE=hfWhat is the relationship between energy and frequency?i.e. if the frequency goes up, what happens to the energy?(h always stays the same it is constant)RecallIn excited atoms an electron from a lower energy level is given energy to move to an outer shell.
34 Binding energy – energy required to free electrons from their atomic orbit Half filled electron shells more stable so higher binding energyElectrons in outer orbits are shielded from the pull of the nucleus so lower binding energy
35 Energy level number Orbital letter 1 K 2 L 3 M 4 N 5 O 6 P Maximum electrons28183250…..PONMLK