Topic 4 - Oscillations and waves Flashcards
What are examples of oscillations?
- Tides of the ocean
- The movement of our legs when we walk
- A heart beating
- Clock mechanisms
- Atoms vibrating
- Machinery and engines
- A guitar string played
- Eardrums
- Radio waves and microwaves
What is the displacement of an oscillator (x)?
The distance in a specified direction from its equilibrium position
What is amplitude (x0)?
The maximum displacement, the distance from the equilibrium position to the furthest point of travel
What is period (T)?
The time it takes for one complete oscillation
What is frequency (ƒ)?
The number of oscillations in unit time (second)
What is the relationship between frequency and period?
What is phase difference?
The angle (radians) between two similar oscillations
What is angular frequency (angular speed)(ω)?
Unit: rads–1
What is simple harmonic motion?
An oscillation in which the acceleration (a) of a body is proportional to its displacement (x) from its equilibrium position and in the opposite direction
What is the interchange between kinetic energy and potential energy during SHM?
All mechanical oscillations involve a continual interchange between kinetic energy and some form of potential energy
What is the kinetic energy, potential energy, and total energy of SHM?
What is damping?
The dissipation of energy of an oscillator due to resistive forces
What are the types of damping?
- Light damping
- Heavy damping
- Critical damping
What is natural frequency of vibration?
When something is disturbed and then left to osillate without further interference, it is said to oscillate at its natural frequency of vibration
What is forced oscillation?
Occurs when an external oscillating force acts on another system tending to make it oscillate at a frequency which may be different from its natural frequency
What is resonance?
The increase in amplitude and energy of an oscillation that occurs when an external oscillating force has the same frequency as the natural frequency of the system
What are examples of unwanted resonance?
- Parts of engines and machinery vibrate
- Earthquakes
- Strong winds can cause resonance in bridges
What are examples of useful resonance?
- Radios and TVs are tuned by changing the frequency to mach the transmitted signal
- Quartz crystals can be made to resonate and it’s useful in driving accurate timing
- Magnetic resonance imaging (MRI)
What are continuous progressive (travelling) waves?
Waves which transfer energy away from a source
What is a wave pulse?
A wave formed from a disturbance of single oscillation (not continuous)
Do progressive (travelling) waves transfer energy?
Yes.
Describe transverse waves?
- Parts of the medium are not all moving in phase
- Each part of the medium oscillates perpendicularly to the direction in which the wave is transferring energy
- They have troughs and crests
e. g. light and other EM waves and water waves
Describe longitudinal waves
- Each part of the medium oscillates parallel to the direction in which the wave is transferring energy
- Have compressions and rarefactions
- The medium in which the wave transfers energy does not undergo net translational motion away from the source
e. g. sound and eartquakes
What is a wavefront?
A line joining adjacent points moving in phase in a wave
How can wavelength be determined from wavefronts?
The distance between adjacent wavefronts is the wavelength
What is a ray?
A line pointing in the direciton in which the wave is transferring energy
What is the intensity (I) of a wave?
The wave power passing through unit area
Unit: Wm–2
What is wavelength (λ)?
The shortest distance between two points moving in phase
What is wave speed?
The distance travelled by a wave (wavefront) in unit time
What is the relationship between wave speed, wavelength, and frequency?
v = ƒλ
Do all electromagnetic waves travel with the same speed in free space?
Yes
What happens to waves when they are reflected on a surface?
The angle of incidence (i) is equal to the angle of reflection (r)
What happens to waves when they travel into a different medium?
Their speed changes
What is refractive index (n)?
The ratio of the speeds of the wave in the two media and also of the angles of indicendence and refraction
What is Snell’s law?
What is diffraction?
The effect when waves pass through gaps (apertures) or pass around obstacles in their path and spread or bend around them
Describe the diffraction around different gaps and obstacles
What are examples of diffraction?
- Sound is diffracted around corners, buildings, doors, and furniture
- Light is diffracted in the eye
- Radio waves need to diffract around buildings and various obstacles to reach the receivers
- The diffraction of X-rays is used to study the arrangement of atoms
What is the principle of superposition?
At any moment the overall displacement at any point will be the vector sum of all the individual wave displacements
What is constructive interference?
- Occurs when coherent waves arrive at a point in phase
- Occurs when the path difference is equal to a whole number of wavelengths:
path difference = nλ
What is destructive interference?
- Occurs when coherent waves arrive at a point exactly out of phase
- Occurs when the path difference equals to an odd number of half wavelengths:
path difference = (n + 1/2)λ
