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Description
Flashcards by Moa Lindström, updated more than 1 year ago
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Created by Moa Lindström
over 10 years ago
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| Question | Answer |
| Examples of oscillations | a pendulum, a swing, a car going over bumps |
| Cycle | one cycle is defined as one complete oscillation of the pendulum (A-B-A). (the term cycle is also used to describe circular motion; one cycle is one complete circle or 2pi radians) |
| Equilibrium position | the position where the pendulum bob would rest if not disturbed - this is position O |
| Amplitude (x0) | the amplitude is defined as the maximum displacement from the equilibrium position, this is distance OB or OA, (m) |
| Time period (T) | time taken for one complete cycle (seconds) |
| Frequency (f) | number of cycles that the pendulum makes per unit time. this is equal to 1/time period. (s^-1 or hertz (Hz)) |
| Angular frequency (w(curved "w" really...)) | found by multiplying f by 2pi (w=2pi f). this quantity is normally used when describing circular motion. an angular frequency of 2pi rads s^-1 means that a body makes one revolution per second. however, it is also used to describe an oscillation, 2pi being equivalent to one complete cycle. (s^-1 or Hz) |
| When stretching a spring, the tension is... | ...proportional to the extension |
| Simple harmonic motion (SHM) | the acceleration is proportional to the distance froma fixed point. the acceleration is always directed towards a fixed point |
| When calculating cos wt, you must have your calculator set on... | ...radians |
| Interchange between KE and PE during SHM | at the top of the swing the mass (pendulum) has maximum PE and minimum KE. at the bottom of the swing the mass has maximum KE and minimum PE |
| Total energy | total energy=KE+PE |
| Potential energy | potential energy at any moment = total energy - KE |
| Light damping | if the opposing forces are small, the result is a gradual loss of total energy. this means that the amplitude of the motion gets slowly less with time. |
| Critical damping | critical damping occurs if the resistive force is so big that the system returns to its equilibrium position without passing through it. this would be the case if a mass on a spring were suspended in for example oil |
| Forced oscillation | if a system is forced to oscillate at a frequency other than the natural frequency |
| Resonance | increase in amplitude that occurs when an oscillating system is forced to oscillate at its own natural frequency |
| In phase | same displacement at the same time |
| Out of phase | different displacement at same time |
| Reflection (of a (water) wave) | if a water wave hits a wall, the waves reflect |
| Refraction | change of direction, waves are bending |
| Interference | when two waves cross each other, they can add together (or cancel out) creating an extra big wave (or result in no wave!) |
| Diffraction | when (water) waves pass through a small opening the waves spread out |
| Also waves | anything that reflects, refracts, interferes and diffracts can also be called a wave |
| Wave pulse | (if a string held between two people is displaced (flicked),) a disturbance can be seen to travel from one end to another |
| Wave speed | the wave pulse travels with a certain speed, distance travelled by the wave profile per unit time (if a string held between two people is flicked and creates a wave) |
| Transfer of energy | as a string is lifted up, it is given PE. this PE is transferred along the string, and a wave can therefore be thought of as a transfer of energy |
| Wave properties | |
| Example of transverse waves | wave in a string, light. (the direction of disturbance is perpendicular to the direction that the wave profile moves) |
| Example of longitudinal waves | sound, compression wave in a slinky. (the disturbance is parallel to the direction of the wave) |
| What type of waves can be polarized? | only transverse waves. a wave is polarized if the displacemnt is only in one direction |
| Constructive interference | two in phase waves add to give a wave of twice the amplitude |
| Destructive interference | two out of phase waves cancel |
| Wave poperties, two-dimensional waves | |
| Wavefront | this is a line joining points that are in phase, straight or circular lines |
| Rays | rays are lines drawn to show the direction of the waves - they are always at right angles to the wavefront |
| Circular wavefronts | produced by a point disturbance. the rays are radial, as they are perpendicular to the wavefronts. (for example a waterdrop landing in a pool of water - point disturbance) |
| Plane wavefront | produced by an extended disturbance, for example a long piece of wood dipped into the water, or a point that is so far away that the circles it produces look like straight lines |
| Reflection | when a wave hits a barrier, it is reflected. note that the reflected wave appears to originate from somewhere on the other side of the barrier, same as when looking at yourself in a mirror |
| The laws of reflection | describes how waves are reflected of barriers. ~the angle of incidence = the angle of reflection. ~the incident and reflected rays are in the same plane as the normal |
| Transmitted part of a wave | the part of the wave that passes through a medium; not reflected |
| Refraction | the change of direction when a wave passes from one medium to another |
| Snell's law | sin i(ncident)/sin r(efracted)=v1/v2 |
| Refractive index | the ratio of the velocity of light in the two medias, found by using Snell's law. if the refractive index is large then the light is refracted by a large angle |
| Refractive index of water, glass and diamond | water - 1,33. glass - 1,50. diamond - 2,42 |
| Diffraction | takes place when a wave passes through a small opening. if the opening is very small, then the wave behaves just like a point source |
| Phase angle | if the waves are completely out of phase then phase angle = pi. if not completely out of phase, the phase angle can be calculated from the path difference (d). phase angle (strange "t"-looking symbol)=2pid/lambda (wavelength) |
| Standing (stationary) wave | if a continuous wave is sent along a rope, the original and reflected wave superpose to produce a wave where the peaks simply move up and down but don't progress along the rope. occurs whenever two identical waves travelling at opposite directions superpose. the wave profile doesn't progress |
| Antinode | the opposite of a node... maximum amplitude, 2A since two waves add together |
| Node | the opposite of an antinode... minimum displacement, A=0 |
| Differences between progressive waves and standing waves | ~the wave profile of a standing wave doesn't progress. ~all points in between teo nodes on a standing wave are in phase whereas points in a progressive wave that are closer than one wavelength are all out of phase. ~all points on a progressive wave have the same amplitude, but on a standing wave some points have zero amplitude (nodes) and some points have large amplitude (antinodes) |
| Formula for calculating frequency for a standing wave (with nodes as ends) | f=v/lambda |
| Calculating wave speed (v) in a string | v= (square root of) T/u. T= tension, u (greek letter "miu"(??)) =mass per unit length |
| Sound wave | a propagation of disturbance in air pressure. the change in air pressure causes the air to move backwards and forwards in the direction of the propagation |
| When a standing wave is formed in a closed pipe, only _____ harmonics are formed | odd |
| A standing wave in an open pipe will have ___________ at both ends | antinodes |
| The Doppler effect | "eeeeeeeeeeeeoowwwwwww" sound, the sound on approach is a higher frequency than on retreat. can occur when the source of the sound is moving or when the observer is moving, or when both is moving |
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