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Waves
| Question | Answer |
|---|---|
| Define transverse wave | An oscillating system where the disturbance causing the wave is perpendicular to the direction of propagation of the wave |
| Define longitudinal wave | An oscillating system where the disturbance causing the wave is in the same direction as the direction of propagation of the wave |
| Define progressive wave | A wave that is unbounded and therefore travels outward from its source |
| Define mechanical wave | A wave that causes oscillations of particles in a solid, liquid or gas and must have a medium to travel through |
| Define electromagnetic wave | Cause oscillations in electrical and magnetic fields |
| Define equilibrium position | The position in which the resultant force on an oscillating body would be at rest if it were not oscillating |
| Define amplitude | The maximum displacement from the mean position |
| Define wavelength | The length of one complete cycle or oscillation |
| Define peak | The highest point above the rest position |
| Define trough | The lowest point below the rest position |
| Define frequency | The number of cycles per unit time |
| Define period | The time taken for one complete cycle |
| What is the equation linking period and frequency | T=1/f |
| What is the equation for wave speed | v=fλ |
| Describe how to measure the speed of sound in air | -Person A raises hand and fires air horn -Person B starts stopwatch when they see the hand -Person B stops stopwatch when they hear the horn -Speed of sound can be calculated using speed=distance/time |
| What is the speed of sound in air | 330m/s |
| What is the equation to calculate radians | arc length/radius = radians degrees x π/180 = radians |
| When are two waves in phase | -When they have the same timing wavelength and velocity -Displacements are the same at all times |
| Give two examples of transverse waves | -EM waves -Water waves |
| Give two examples of longitudinal waves | -Sound -Ultrasound |
| When are two waves of the same frequency and wavelength coherant | Constant phase difference between them |
| What is the equation for resonant frequency of the first harmonic | f=1/2L √(T/μ) |
| Define Node | A point on a standing wave where the amplitude is zero |
| Define Antinode | The point on a standing wave where the amplitude is at its maximum |
| What is the theory of superposition of waves | When two waves of the same type interact, the displacement of the new wave produced at that instant is equal to the vector sum of the displacements of the individual waves |
| What is constructive superposition | Superposition in which the two waves that combine are in phase |
| What is destructive superposition | Superposition in which the two waves that combine are out of phase |
| What is total destructive interference | If two waves with equal and opposite displacements meet they will completely cancel each other out |
| Define plane polarised transverse wave | A transverse wave in which the direction of oscillation and the direction of travel are in the same plane |
| What do we call the second polarising filter | analyser |
| What happens if the analyser is perpendicular to the polarising filter | No light can pass through |
| How do we use polarizing filters | -Camera lenses and sunglasses |
| What is a pulse | Several wavelengths |
| Define diffraction | Spreading of wave energy into area that (if the wave had travelled in a straight line have been in shadow |
| How does slit size affect diffraction | Slit much bigger than the wavelength-> No diffraction Slit several wavelengths-> Some diffraction Slit same size as wavelength-> Maximum diffraction Slit smaller than wavelength-> Mostly reflection |
| What happens when you shine monochromatic light through a single slit. | It produces a diffraction pattern with a large central fringe with alternating light and dark fringes on either side. these fringes are caused by interference |
| Define intensity | Power per unit area |
| What happens when we increase the slit width for single slit diffraction | Slit width up, diffraction down, Width of central maximum down, Intensity up, |
| Why does white light split when it is shined into a prism | High frequencies (blue) are refracted more than low frequencies red. |
| What is needed for two source interference | The two waves must be coherent and in phase |
| For two source interference what happen if there is a path difference of nλ wavelengths | Constructive interference |
| For two source interference what happen if there is a path difference of (n+1/2)λ wavelengths | Destructive interference |
| What is huygen's secondary source theory | Every point on a wavefront acts as a secondary source. The new secondary wavefront is the envelope of the secondary wavelets created from the secondary sources |
| What is newtons corpusclar theory | Light is made up of particles called corpuscles |
| How did Newton's corpuscular theory explain reflection | There was a force that pushed the particles of the surface |
| How did Newtons corpuscular theory explain refraction | Light travelled faster in a less optically dense material |
| How does young's double slit experiment prove that light was a wave | An alternating light/dark pattern is formed , this proves that light is a wave as if it was a particle it would just create two light fringes |
| Why can't you use two lamps for the young's double slit experiment | -Not monochromatic -Different frequencies -Not identically timed |
| Why was Huygens theory rejected | Couldn't explain polarisation or double refraction |
| What is the photoelectric effect | When a surface is exposed to EM radiation electrons are emitted |
| How did Hertz's experiment prove that light is a particle | -Emission of e- does not take place below the threshold frequency -No of e- emitted per second ∝ intensity provided that f > threshold -Emission is instantaneous -Wave theory cannot explain this as emission should occur at low f but would take longer |
| What is the equation for energy of a photon | E=hf |
| When can an electron leave the metal in photoelectric emission | If hf>ϕ |
| What is the equation for maximum kinetic energy of a photon | Ekmax=kf-ϕ |
| How can you attract electrons back to the metal | Positively charging metal |
| Define stopping potential | Minimum potential that needs to be applied to a plate to attract all electrons emitted from the surface back to the surface |
| Define de broglie hypothesis | Matter particles have a wavelike nature characterised by the de broglie wavelength |
| Define de broglie wavelength | The wavelength of a matter particle= h/p where p is momentum |
| What is the equation for a diffraction grating | nλ=dsinθ |
| Describe the image formed by an object positioned beyond 2F (lenses) | -Real -Inverted -Smaller than object -Forms between F and 2F |
| Describe the image formed by an object positioned at 2F (lenses) | -Real -Inverted -Same size as object -Forms at 2F |
| Describe the image formed by an object positioned between F and 2F (lenses) | -Real -Inverted -Larger than object -Forms beyond 2F |
| Describe the image formed by an object positioned at F (lenses) | -Image forms at infinity -Rays never meet |
| Describe the image formed by an object positioned closer than F (lenses) | -Virtual -Right way up -Larger than object |
| Define oscillation | A reciprocating back and forth motion about an equilibrium point |
| Define displacement | The displacement of an oscillating body at a time is the distance and direction of that body from the equilibrium position at that time |
| Define one cycle | One complete movement of an oscillating system from its equilibrium position, to the amplitude of its displacement in one direction to the amplitude of its displacement in the other direction and finally back to its equilibrium position once again |
| Define antiphase | Displacements are exactly half an oscillation apart, phase difference is π radians |
| Define standing wave | Created when two progressive waves that are travelling in opposite directions at the same speed meet |
| Define intensity | Energy passing through the unit area per unit time |
| Define wavefront | A line joining identical points on adjacent waves that are in phase |
| Define ray | Direction of energy travel, perpendicular to wavefront |
| Define refraction | The bending of waves at an interface due to the change in speed of the wave as it moves from one medium to another |
| Define wave | The process by which energy is transferred from one place to another without permanent displacement of particles |
| Define inverse square law | Intensity of flux at a distance from a point source is inversely proportional to the distance from the point source squared |
| What is the value of the electron volt | 1.6x10^-19 J |
| Define excitation | The process by which an atom absorbs energy without becoming ionised due to an electron moving from an inner shell to an outer shell |
| Define threshold frequency | The minimum frequency of EM radiation that can cause the photoelectric effect |
| Define work function | The minimum energy needed to release the least strongly bound surface electrons from the metal |
| Define ionisation energy | The energy needed to free an electron from the influence of the nucleus |
| What are the conditions for the formation of a stationary wave | -Same wavelength/frequency -Equal and opposite velocities -Same amplitude |
Created by:
Liam P
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