Random physics stuff I didn't previously have a flashcard for
How has knowledge and understanding of EM radiation changed over time
End of 17th century - 2 theories published
Newton - light is composed of ‘corpuscles’ (tiny particles)
Huygens - light is composed of waves
Young’s double slit provided evidence for light as waves
Then later Einstein provided evidence for light as particles
Conclusion - it’s both
Applications of diffraction gratings
Used by chemists and astronomers to identify elements - more accurate than prisms
E.g. X-Ray crystallography and analysing the elements present in stars - split up light from a star to form a line absorption spectra
X-Ray crystallography
X-Rays are diffracted by the atoms of crystalline solids
Forms a diffraction grating
Atoms act as a diffraction grating
Used to identify elements
Used in the discovery of DNA structure
Out of phase
Destructive interference
Phase difference of pi radians or 180 degrees
Resonance, displacement and periodic force
Phase difference of 1/2 pi radians between displacement and periodic force
Differences between stationary waves and progressive waves
In a stationary wave points of a particular phase remain in the same location as time passes, but in progressive waves the points of the given phase travel forwards
In a stationary wave, no energy is transferred along the wave (from one point to another) it instead stores energy in ‘pockets’ whereas a progressive wave transfers energy
Stationary waves, nodes and antinodes for open ends and fixed (closed) ends
Open end -> antinode
Closed end -> node
SHM amplitude and displacement definitions
Displacement is the distance from equilibrium
Amplitude is maximum displacement
Brownian motion conclusions
Movement of smoke particles caused by collisions by randomly moving air molecules
Smoke particles are visible but air molecules are not hence air molecules must be very small
Small movement of smoke particles is due to the large number of air molecules from all sides
Boyle’s law definition
Pressure is inversely proportional to volume for a fixed mass of gas at a constant temperature
Single slit diffraction pattern
Wider central maximum surrounded by other lower intensity maxima with dark minima between maxima
Impact of increasing wavelength on diffraction pattern
Larger fringe spacing
Wider central maxima
Impact of using a light source which emits a range of wavelengths on the interference pattern
Central maxima unchanged in width (depending on the range)
Broader maxima and maxima get even broader as order increases
Equation for calculations involving mol
N = nNa
N is number of atoms
n is number of moles
Na is Avagadro’s constant
Widths of central maximum
Increasing slit width decreases the amount of diffraction - decreases width of central maximum (gets narrower) and increases its intensity
Increasing wavelength increases diffraction - central maximum is wider and intensity is lower
Phase difference for two points on the same wave
The phase difference of two points on a wave is the difference in their positions in the wave’s cycle
Resonant frequencies on a string - stationary waves
A frequency at which a stationary wave is formed because an exact number of waves are produced in the time it takes for a wave to get to the end of the string and back again
An exact number of half wavelengths fit on the string
The string vibrates at maximum amplitude
Observing stationary waves using sound waves and microwaves
Use a loudspeaker to direct sound waves into a glass tube with a flat end to reflect them, put powder in the tube and it will collect at the nodes
Use a metal plate to reflect microwaves and a probe to observe the nodes and antinodes
Why does f decrease when L increases
The harmonic frequencies correspond to the number of half wavelengths on a string
If the length is increased, the wavelength of the resonant frequency would also increase
Speed of the wave must remain constant so f must increase
Can also use the formula for the first harmonic to reason this
Why is a laser better than white light for producing a clear diffraction pattern?
Laser light is monochromatic - all the same wavelength, all diffract by the same amount giving sharp, bright fringes
White light is made up of a range of wavelengths which diffract by different amounts
How to create coherent sources of sound waves and light
Connect two loudspeakers to a single amplifier
Direct monochromatic light into a double slit
Investigating the interference and diffraction pattern of sound waves and microwaves
Attach two loudspeakers to an amplifier and create sound waves at a set frequency, walk along a straight line parallel to the line of the speakers and mark the minima and maxima
Same for microwaves except using microwave emitters and a probe