Topic C Key Terms Flashcards
What is SHM behaviour
The acceleration (or restoring force) is DIRECTLY PROPORTIONAL to the displacement from the rest point.
The acceleration is always towards the rest point.
what is the phase difference of one oscillation
One oscillation is from 0 radians to 2π radians.
What is the gradient of a T^2 on y axis, and mass on x axis graph
4pi^2/k
How does energy vary with time over one oscillation?
SHM systems constantly transfer energy between PE and KE.
Total Energy = KE + PE at all times.
Total Energy will be equal at all times (no energy loss).
How does energy vary with displacement x ?
SHM systems constantly transfer energy between PE and KE.
Total Energy = KE + PE at all displacements.
Total Energy will be equal at all displacements (no energy loss).
The energy graphs must not extend beyond the amplitudes.
If you start at the rest point, which formula should you use?
x = A . Sin (ω.t)
v = A.ω . Cos (ω.t)
a = - A.ω2 . Sin (ω.t)
so a = - ω2
A. Sin (ω.t)
(Hence a = - ω2 . x )
If you start at the amplitude which formula should you use?
x = A . Cos (ω.t)
v = - A.ω . Sin (ω.t)
a = - A.ω2 . Cos (ω.t)
(Hence a = - ω2 . x )
Where is max KE in a pendulum?
KEmax = Total Energy when x = 0 since the object is at max speed at the rest point and there is no PE since there is no restoring force at the rest point.
Mechanic waves
A wave that requires a physical medium through which to travel. Example - sound waves. Sound waves can not travel through a vacuum (empty space).
Electromagnetic Waves
Do not require a physical medium through which to travel. Electromagnetic waves can travel through a vacuum. Examples: Radio waves, visible light, x-rays, etc. All EM waves travel at the same speed (speed of light) in a vacuum.
Wave
A periodic disturbance that transfers energy through a medium.
Medium
The material through which a wave travels.
Transverse Wave
A wave in which the particles of the medium move perpendicular to the direction of energy transfer the wave motion.
Examples of transverse waves: EM Waves (light), water surface waves
Longitudinal Wave
A wave in which the particles of the medium move parallel to the direction of energy transfer.
Displacement (x)
Displacement, (distance with direction), that a given particle in the medium is from its rest point. Measured in metres.
Amplitude (A or Xo)
maximum displacement from the rest point. Measured in metres.
Time Period (T)
the time taken for one complete wave to pass a fixed point. Measured in seconds.
Frequency(f)
number of complete waves that passes a fixed point in one second. Measured in Hertz.
Wavelength (𝜆)
the distance from a peak to the next consecutive peak. Measured in metres.
Wave speed (v)
the distance that a given wave-front/peak progresses in one second. (m.s-1)
v = f . 𝝀
Intensity (Link to apparent brightness)
is the incident power of a wave per unit area. Units of intensity are (W.m-2)
I = P / area
what is Constructive Interference
Two or more waves meet at a point. If they are IN PHASE the resultant Amplitude increases. This is CONSTRUCTIVE INTERFERENCE.
what is Destructive interference
Two or more waves meet. They are OUT OF PHASE and this results in a decreased Amplitude we call this DESTRUCTIVE INTERFERENCE.
what is Principle of Superposition
The principle of superposition is that the resultant displacement at any point is the algebraic summation of the displacements of the individual waves at that point.
What is path difference
Two (or more) wave trains can be in phase, or out of phase etc……
They can be moved in or out of phase depending on the relative distance between them this is called a PATH DIFFERENCE.
What path difference will allow the waves will meet in phase and there will be constructive interference?
If the PD is 0, λ, 2λ, 3λ
What path difference will allow the waves will meet out of phase and there will be destructive interference.
If the PD is ½ λ, 3/2 λ, 5/2 λ
what is a ray
A ray is a straight line (with an arrow) that indicates the direction of energy propagation.
what are wave fronts
A wavefront is a line connects places of equal phase, say the crest of the wave.
Wavefronts are always perpendicular to the ray.
explain why frequency does not change during refraction
If frequency were to change during refraction, the transmitted wave would become of out phase with the incident wave
and therefore energy would be transferred before or after it were to arrive at the interface
and this would mean that energy was not being conserved.
Why does a minimum occur? in a Single Slit Diffraction Pattern
Two waves meet and interfere
The two waves are out of phase (π out of phase) (in anti-phase)
Destructive superposition occurs
There is zero (or a minimum) brightness/intensity.
what are the minimas and maximas in a single slit light patter
Then minimas (dark fringes) and less bright maximas (bright fringes).
What causes the First Order Minimum? in a Single Slit Diffraction Pattern
2 waves meet
The 2 waves are completely out of phase
Destructive interference occurs
The First Order Minimum
what is the formula for the Angle of the First Order Minimum
ϴ = λ / b
what are coherant sources:
This means they have the same frequency and a constant phase difference (in this case they are in phase)
what is fringe separation
Between one maxima and the next maxima
What causes the First Order Minimum?
Two waves meet on the screen and interfere
The two waves are out of phase (π out of phase) (in anti-phase)
Destructive superposition occurs
There is zero (or a minimum) brightness/intensity.
how to draw a single slit diffraction pattern
Note the general shape with bright central maximum
1st order maximas no higher than 1/3 of the central maximum
the width of the first order maximum is equal to the distance from the centre point to the first order minimum
𝜃 = 𝝺/b so if b is doubled the pattern will be half the width
a wider slit will allow through more light energy so intensity is greater
𝜃 = 𝝺/b so if b is halved the pattern will be twice as wide
a narrower slit will allow through less light energy so intensity is reduced
what are diffraction gratings
Basically a very high number of slits, with very fine slit spacing and width. Oftens hundreds of slits per mm.
what are the characteristics of diffraction gratings
Maximas are very intense
Mini-maximas become zero
Wide fringe spacing
No modulation by single slit diffraction pattern
Excellent choice for analysing a spectrum (eg. star light)
Small ranges of wavelengths can be measured
