Waves

• Progressive waves transfer energy without transferring matter.
• Transverse waves is when the oscillation of particles is at right angle to the direction of energy transfer.
• All electromagnetic waves are transverse.
• Longitudinal waves is when the oscillations of particles are parallel to the direction of energy transfer.
• Longitudinal waves cannot travel in a vaccum.
• Polarised waves oscillate in only one plane.
• Polaroid glasses are an example of polarization or waves being polarised. They reduce glare by partially blocking polarised light.
• TV and Radio signals are another example of polarised waves. The receiving aerial must be aligned in the same plane polarization to receive the signal at full strength.
• Superposition is where the displacements of two waves are combined as they pass each other, the resultant displacement is the vector sum of each wave’s displacement.
• A stationary wave is formed from the superposition of 2 progressive waves, travelling in opposite directions in the same plane, with the same frequency, wavelength and amplitude.
• In phase, constructive interference occurs so antinodes are formed, which are regions of maximum amplitude.
• Completely out of phase, destructive interference occurs and nodes are formed, which are regions of no displacement.
• Formation of a stationary wave: 


  A wave travelling down the string from the oscillator will be reflected at the fixed end of the string, and travel back along the string causing superposition of the two waves, and because the waves have the same wavelength, frequency and amplitude, a stationary wave is formed.
• The distance between adjacent nodes or antinodes on a standing wave is called half-wavelength (λ/2).
• The lowest frequency at which a stationary wave forms is the first harmonic.
• μ is the mass per unit length.
• Path difference is the difference in the distance travelled by two waves.
• A coherent light source has the same frequency and wavelength and at a constant phase difference.
• Monochromatic emit a single wavelength of light.
• Destructive Interference occurs where the path difference is a whole number and a half wavelengths ((n+½)λ).
• Destructive Interference


  Dark fringes are formed where the light meets completely out of phase and interferes destructively, this occurs where the path difference is a whole number and a half wavelengths ((n+½)λ)
• Constructive Interference


  Bright fringes are formed where the light meets in phase and interferes constructively, this occurs where the path difference between waves is a whole number of wavelengths (nλ, where n is an integer).
• Using white light instead of monochromatic laser light gives wider maxima and a less intense diffraction pattern with a central white fringe with alternating bright fringes which are spectra, violet is closest to the central maximum and red furthest.
• Safety precautions when using lasers: ● Wear laser safety goggles ● Don’t shine the laser at reflective surfaces ● Display a warning sign ● Never shine the laser at a person. This is to prevent Eye damage.
• Knowledge and understanding of any scientific concept changes over time in accordance to the experimental evidence gathered by the scientific community.
• Diffraction is the spreading out of waves when they pass through or around a gap
• The greatest diffraction occurs when the gap is the same size as the wavelength.
• The diffraction pattern for white light has a central white maximum with alternating bright fringes which are spectra, violet is closest to the central maximum and red furthest away.
• The maximum value of sin θ is 1, therefore any values of n, which give sin θ as greater than 1 are impossible.
• There are several applications to diffraction grating, such as X-ray crystallography, optical microscopes, and spectrometry.
• n2 is more optically dense than n1 , therefore the ray of light slows down and bends towards the normal. However, in the case where n2 is less optically dense than n1 the ray of light will bend away from the normal.
• Increasing the slit width decreases the amount of diffraction so the central maximum becomes narrower and its intensity increases.
• Increasing the light wavelength increases the amount diffraction as the slit is closer in size to the light’s wavelength, therefore the central maximum becomes wider and its intensity decreases.
• Amplitude is the maximum displacement of a wave from its undisturbed position
• Frequency is the amount of oscillations per second
• Wavelength is the distance between two adjacent points on a wave.
• Wave speed is distance travelled by the wave per unit time.
• Phase is how far through a cycle a wave is.
• Phase difference is the difference in the phase of two waves.