Class 7 Flashcards
What is Hooke’s Law?
F = -kx
F = restoring force k = spring constant (spring-dependent) `x = displacement from zero (relaxed position)
In a spring, what is amplitude?
The maximum value that x will have
How do you calculate the energy stored in a spring as it stretches/compresses?
PEelastic = 1/2kx^2
When a compressed spring extends, what is the work done by the spring?
Wby spring = - (delta)PEelastic
Does conservation of mechanical energy apply for a spring?
Yes
KEi + PEi = KEf + PEf
When is the maximum KE and PE of a spring?
Maximum KE is passing through equilibrium, moving quickly.
Maximum PE occurs when fully stretched or fully compressed.
What is the period in SHM?
The time it takes to complete one cycle
How do you calculate frequency?
f = 1/T
How do you calculate frequency for springs?
f = 1/2pi sqr.rt (k/m)
How do you calculate frequency for a pendulum?
f = 1/2pi sqr.rt (g/L)
L = length of pendulum arm g = gravity
What is the restoring force for a pendulum?
Frestore = mgsin(theta)
What is a transverse wave?
A medium that oscillates perpendicular to the direction of wave propagation.
e.g. string, EM waves
What is a longitudinal wave?
A medium that oscillates parallel to direction of wave propagation.
e.g. sound (longitudinal pressure wave)
What is the opposite of wave compression?
Wave rarefaction (spreading out)
With regard to wave speed:
v =?
v = lambda x f
What determines the speed of a wave?
The medium and type of wave and physical properties of a medium
What is constant for all waves in a certain medium?
v
frequency or wavelength can change, however
What stays the same for waves when moving from one medium to another?
frequency
What determines the speed of a wave in a string?
v = sqr rt. (tension/linear density)
Do sound wave travel slower (than air) in water?
No, faster!
Sound waves are slowest in gases, faster in liquids, and fastest in solids
What is the trend for sound wave speed in different phases?
Sound waves are slowest in gases, faster in liquids, and fastest in solids
What is the beat frequency?
Cycles between constructive and destructive interference.
fb = | f1 - f2 |
What is a standing wave?
A wave that is “waving” but not propagating because it is interacting with its own reflection (caused by a closed end of a tube) or tied down at both ends.
What is a first harmonic wave?
n=1
A string tied at each end. 2 nodes and 1 antinode.
Length of strand is 1/2 of a wave so L = 1/2lambda
What is a second harmonic wave?
n=2
3 nodes, 2 antinodes
L = lambda
What is the generic equation for wavelength (lambda) of a string:
lambda(sub n) = 2L/n
What is a third harmonic wave?
n=3
4 nodes, 3 antinodes
L = 3lambda/2
In terms of waves, intensity I = ?
I = Power/Area
Power is the total energy
But intensity is per unit area so kids and adults can wear the same strength sunscreen.
With regards to a spherical wave, how does intensity relate to distance from source?
I : 1/r^2
How does intensity relate to amplitude?
I : A^2
Essentially the energy of a wave and the amplitude of a wave are directly related (shocker!)
How do you human ears respond to sound intensity (mathematically)?
Logarithmically, which enables a larger sensitivity range
What is the threshold for hearing?
Io = 10^-12 W/m
What is the dB equation for hearing equation? What is the trick?
beta = 10log(sub10) I/Io
For every increase in the I by a factor of 10, ADD 10 to beta
For every decrease in I by a factor of 10, SUBTRACT 10 from b
What is the doppler shift when the detector and the source get closer?
Higher detected frequency
What is the doppler shift when the detector and the source get farther away?
Lower detected frequency
What is the speed of sound in air?
350 m/s
What is the equation for doppler shift?
x
What is alpha emission?
Loss of 2 protons and 2 neutrons ->
Atomic number decreases by 2, mass number decreases by 4
Is exposure to alpha decay?
Safe unless consumed
What is beta emission?
Electron emission:
Loss of 1 electron from a neutron that gets split into an electron and a proton ->
atomic number increases by 1, mass number does not change
ORRRR
Positron emission:
A proton splits into a positron which is emitted and a neutron ->
Atomic number decreases by 1, mass number does not change
What is electron capture?
A proton is combined with a (captured) electron to make a neutron.
Atomic number decreases by 1, atomic number does not change.
Same result as positron emission!
What is gamma emission?
Atomic number and mass do not change.
Nuclei relaxes from an excited state.
Nuclear reactions are ______thermic?
Exothermic
Decay, fission fusion, etc.
Nuclear fission, fusion, etc.
(delta)E = ?
BEparent - BEdaughter
BE = binding energy
