Les Vagues Flashcards
What is wavelength?
distance btw 2 successive pts (eg consecutive crests/troughs) in a wave which are in phase
Consider a wave of amplitude A, period T, what are 2 possible displacement-time eqn?
y = Asin(2πt/T)
OR
y = Acos(2πt/T)
From a graph, how to know motion of particle?
Draw same graph slightly to the right; next waveform (to show particle’s position at next instant)
eg at amplitude particle is instantaneously at rest
What are the meanings of:
- in phase
- in antiphase
- out of phase
- In phase
when 2 oscillating particles hv φ of 0 or any integer multiple of 2π - In antiphase
When 2 oscillating particles hv φ of π or any odd integer multiple of π - Out of phase
when 2 oscillating particles hv φ other than 0 or any integer multiple of π (any other angle; NOT to confuse w antiphase)
*NOTE: don’t forget that φ is in rad
What is the eqn of phase diff, φ, for distance and time?
- distance:
φ = 2πx/λ - time:
φ = 2πt/T
How to derive v=fλ?
- Consider wave of wavelength λ, period T
- From def n of wavelength, in 1 cycle, wave energy moves distance λ, & time taken for 1 cycle is T
- Speed v is distance moved per unit time
v= λ/T - Since f is related to T by f=1/T, thus
v=f λ
Define transverse and longitudinal wave
- Transverse wave is one in which direct n of oscillat n of particles is perpendicular to direct n of energy transfer of wave
- Longitudinal wave is one in which direct n of oscillat n of particles is parallel to direct n of energy transfer of wave
What is relationship between energy and amplitude of wave?
energy is directly proportional to square of amplitude
Define intensity
power per unit area perpendicular to direct n of wave propagat n
eqn: Intensity = Power/Area
intensity … amplitude² ?
is directly proportional to
Intensity of wave at distance, r, fr pt source is given by what eqn?
What can you tell abt this eqn?
Intensity, I = Power/4πr²
*NOTE: surface area of sphere, not volume!
eqn shows inverse square law, where
Intensity is inversely proportional to r²
For a spherical wave emitted fr pt source of constant power,
amplitude … r?
is inversely proportional to
Explain what is polarisation
Said to occur when particles in wave oscillate oni in single direct n perpendicular to direct n of energy transfer of wave
What is Malus’ Law
New Intensity = Icos²θ,
where polarising filter is at an angle θ to polarising axis, and I is og intensity
How does amplitude and intensity of unpolarised light change when it is polarised?
Amplitude same, intensity is halved
What are the wavelengths of electromagnetic spectrum? (hint: Germaine do not…)
C (Cosmic rays) - 10^-12 m
G
X - 10^-9 m
U
V
I - 10^-6 m
M
radar - 10^-3
R - 1m
broadcast band - 10^3m / 1km
*All travel at 3.00 x 10^8 m s^-1 in vacuum
What are the wavelengths of visible light?
- 700nm
R
O
Y - 600nm
G
B - 500nm
I
V - 400nm
Define progressive wave
progressive waves move energy IN DIRECTION OF TRAVEL OF WAVE from place to place without transfer of matter
