LIGHT & WAVES Flashcards
the laws of reflection
- the angle of incidence = the angle of reflection.
2. the incident ray, the normal at point of incidence and the reflected ray all lie in the same plane
real image
formed by the actual intersection of light rays. It can be formed on a screen.
virtual image
formed by the apparent intersection of light rays. It cannot be formed on a screen.
laws of refraction
- the incident ray, the normal at point of incidence and refracted ray all lie in the same plane,
- (Snell’s law) for any pair of media, the sin of i, the angle of incidence, is proportional to the sin of r, the angle of refraction.
i. e. n= sin i/ sin r
the refractive index
the refractive index of a medium is the ratio of the sine of the angle of incidence to the sine of the angle of refraction when light travels from a vacuum into that medium.
n = 1/sin c
the critical angle
he angle of incidence for which the corresponding angle of refraction is 90˚
total internal reflection
When light going from a denser to a rarer medium strikes the second medium with an angle of incidence greater than the critical angle, it does not enter the second medium. It is all reflected back in the denser medium.
wave
a means of transferring energy through a medium, without any net movement of that medium.
transverse wave
in a transverse wave, the movement of the particles is perpendicular to the movement of the wave.
longitudinal wave
in a longitudinal wave, the movement of the particles is parallel to the movement of the waves
diffraction
the ability of a wave to spread out after encountering an obstacle or after passing through a small gap
interference
occurs when two waves meet. When this happens, the total displacement will be equal to the algebraic sum of the individual displacements.
coherent waves
are two or more waves that have the same frequency and wavelength, and that are in phase or maintain a constant phase difference
polarisation
the restriction of a wave to vibrations in one plane only
standing wave
produced when two waves of the same frequency and amplitude meet, moving in opposite directions
harmonics
multiples of the natural frequency of vibration of a body.
resonance
the transfer of energy between two bodies of the same natural frequency
intensity of sound
the intensity of sound at a point is defined as the rate at which energy is crossing a unit area perpendicular to the direction in which the sound is travelling
threshold of hearing
the threshold of hearing is the lowest sound intensity to which an average human ear can respond. Its value is taken as 10^-12 Wm^-2
the frequency limits of audibility
highest and lowest frequency sound waves that the average human can hear.
doppler effect
the apparent change in the frequency of a wave due to the relative motion of the source of the wave or an observer is known as the doppler effect
frequency of a wave
the frequency, f, is the number of cycles completed at any one point per second
period of a wave
the period of a wave, T, is the time taken to undergo one complete cycle
f=1/T
speed of a wave
the speed of a wave, c, is the speed of propagation through a medium.
constructive interference
if the peak of one wave meets the peak of another
destructive interference
if the peak of one wave meets the trough of another
pitch corresponds with
frequency
loudness corresponds with
amplitude
quality corresponds with
the presence of harmonics
Optical fibre
A very thin transparent rod (usually of glass) through which light can travel by total internal reflection
Travelling mechanical wave
A disturbance carrying energy through a medium without any overall motion of that medium
Travelling wave
Either mechanical or electromagnetic is a disturbance that travels out from the source producing it, transferring energy from one source to other places through which it passes
Refraction of waves
The changing of direction of a wave when it enters a region where its speed changes
Constructive interference
When waves from two sources meet and the amplitude of the resulting wave is greater than the amplitudes of each of the individual waves, the waves are said to undergo constructive interference
Destructive interference
When waves from two sources meet and the amplitude of the resulting wave is less than the amplitude of each of the individual waves, the waves are undergoing destructive interference
If λ is the wavelength of travelling waves causing the stationary wave then:
The distance between 2 consecutive nodes is λ/2.
The distance between 2 consecutive antinodes is λ/2.
The distance between an anti node and the next node is λ/4.
Loudness
The loudness of a sound wave depends on the amplitude. The greater the amplitude the greater the sound
Pitch
The pitch of the note depends on the frequency of the sound wave. The higher the frequency the higher the pitch
Quality
The quality of a musical note depends on the number of overtones present in the note and the relative strengths of the different overtones
Fundamental frequency of a string
A string vibrating with an anti node at its centre and a node at each end (and no other nodes or antinodes) is vibrating at its fundamental frequency
Harmonics
Frequencies which are multiples of a certain frequency f are called harmonics. F is called the fundamental frequency or the first harmonic. If f is the first harmonic, 2f is the second
The grating constant
The distance d between two adjacent slits on the grating is called the grating constant or grating spacing
Dispersion
The separating out of the different wavelengths present in light
