Waves and Materials Flashcards
Young Modulus
tensile stress/strain (assuming the limit of proportionality has not been exceeded). The unit of the Young modulus is the pascal (Pa) which is to 1 Nm-2
yield point
point at which the stress in a wire suddenly drops when the wire is subjected to increasing strain
ultimate tensile stress
tensile stress needed to break a solid material
stiffness constant
the force per unit extension needed to extend a wire or a spring
stress
force per unit area of cross section in a solid perpendicular to the cross section
strain
extension per unit length of a solid when deformed
Hooke’s Law
the extension of a spring is proportional to the force needed to extend it up to a limit referred to as its limit of proportionality
elasticity
property of a solid that enables it to regain its shape after it has been deformed or distorted
elastic limit
point beyond which a wire is permanently stretched
breaking stress
tensile stress needed to break a solid material
( means the same as the ultimate tensile stress)
brittle
snaps without stretching or bending when subject to stress
transverse waves
The direction of oscillations are perpendicular to the direction of energy propagation
Longitudinal waves
The direction of oscillations are parallel to the direction of energy propagation
Young’s fringes
parallel bright and dark fringes observed when light from a narrow slit passes through two closely spaced slits
Stationary wave
Wave pattern with nodes and anti-nodes formed by the superposition of two progressive waves of equal amplitude and frequency travelling in opposite directions
amplitude
the maximuum displacement from equilibrium of an oscillating object. For a transverse wave it is the dstance from the middle to the peak of the wave
antinode
fixed point in a stationary wave pattern where the amplitude is a maximuum
coherent
two sources of waves are coherent if they emit waves with a constant phase difference
critical angle
the angle of incidence of a light ray must exceed the critical angle for total internal reflection to occur
cycle
interval for a vibrating particle (or wave) from a certain displacement and velocity to the next time the particle (or wave) has the same displacement and velocity
diffraction
the spreading of waves when they pass through a gap or round an obstacle.
diffraction grating
a plate with many closely ruled parallel slits on it
dispersion
splitting of a beam of white light by a glass prism into colours
ductile
stretches easily without breaking
first harmonic
patten of stationary waves on a string when it vibrates at its lowest possible frequency
frequency
the number of oscillations per second
node
fixed point in a stationary wave pattern where the amplitude is zero
period of a wave
time for one complete cycle of a wave to pass a point
path difference
the difference in distances from two coherent sources to an interference fringe
phase difference
the time between successive instants when two objects are at maximum displacement in the same direction
plane-polarised waves
transverse waves that vibrate in one plane only
progressive waves
waves which travel through a substance (or through space if electromagnetic)
refraction
change of direction of a wave when it crosses a boundary where its speed changes
refractive index
speed of light in free space
speed of light in the substance
superposition
the effect of two waves adding together when they meet
time period
time for one complete cycle of oscillations
wavefronts
lines of constant phase (e.g. wavecrests)
wavelength
the least distance between adjacent vibrating particles with the smae displacement and velocity at the same time
