Waves PDF - AS Level

Waves Progressive wave can transfer energy. Types Particle oscillation is Particle oscillation is parallel to wave energy perpendicular to wave energy direction. direction. Transverse waves...

Waves Progressive wave can transfer energy. Types Particle oscillation is Particle oscillation is parallel to wave energy perpendicular to wave energy direction. direction. Transverse waves Longitudinal waves Parallel Perpendicular  Amplitude (A) is the maximum displacement. The unit is the metre (m). Displacement- distance graph Wavelength (λ) is the distance between two adjacent wavefronts.The unit is the metre (m). Wavefront  Frequency (f) of a wave is the number of complete oscillations of a particle in the wave per unit time. The unit is the hertz (Hz). Displacement – time graph Period (T) is the time taken for one complete oscillation. The unit is the second (s). Measuring  Amplitude Cathode ray oscilloscope screen Time base B B Moving direction at one point A Wave speed Wave motion speed. distance moved by wave wave speed = time taken λ v= = fλ T Unit: m/s C Types of waves 1. Wave can be transferred forwards. 2. Energy can be transferred. Progressive waves Stationary waves Energy of the wave Intensity The intensity of a wave is defined as the rate of energy transmitted (power) per unit area at right angles to the wave velocity. power intensity = area Unit: W/m2 intensity ∝ amplitude2 1 intensiy ∝ distance2 B A D  Wavelength Period Basic term Amplitude Frequency Wave speed The quantities at a real wave Crest Equilibrium position Trough  The quantities at a real wave Compression Rarefaction Phase Phase Phase difference 𝐜𝐡𝐚𝐧𝐠𝐞 𝐢𝐧 𝐭𝐢𝐦𝐞 × 𝟐𝛑 𝐩𝐞𝐫𝐢𝐨𝐝 𝐜𝐡𝐚𝐧𝐠𝐞 𝐢𝐧 𝐥𝐞𝐧𝐠𝐭𝐡 × 𝟐𝛑 𝐰𝐚𝐯𝐞𝐥𝐞𝐧𝐠𝐭𝐡 Phase difference In phase Exactly out of phase 0˚ 180˚ 360˚ B When the source and observer is stationary When source moves towards to the oberver Source is moving towards with higher speed The moving speed is higher than source speed The source is moving away from Source is moving away with source speed Doppler effect Doppler effect Observed frequency is different to source frequency when source moves relative to observer. Move towards Observed frequency is higher. Pitch is higher. Move towards blue in the electromagnetic spectrum. Move away Pitch is lower. Move towards red in the electromagnetic spectrum. Equation Away 𝑣 𝑜𝑏𝑠𝑒𝑟𝑣𝑒𝑑 𝑤𝑎𝑣𝑒𝑙𝑒𝑛𝑔𝑡ℎ 𝜆0 = 𝑓𝑠 𝑣 𝑣𝑓𝑠 𝑜𝑏𝑠𝑒𝑟𝑣𝑒𝑑 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 𝑓0 = = 𝜆0 𝑣 + 𝑣𝑠 𝑣 + 𝑣𝑠 𝑜𝑏𝑠𝑒𝑟𝑣𝑒𝑑 𝑤𝑎𝑣𝑒𝑙𝑒𝑛𝑔𝑡ℎ 𝜆0 = 𝑓𝑠 Equation Towards 𝑣 𝑜𝑏𝑠𝑒𝑟𝑣𝑒𝑑 𝑤𝑎𝑣𝑒𝑙𝑒𝑛𝑔𝑡ℎ 𝜆0 = 𝑓𝑠 𝑣 𝑣𝑓𝑠 𝑜𝑏𝑠𝑒𝑟𝑣𝑒𝑑 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 𝑓0 = = 𝜆0 𝑣 − 𝑣𝑠 𝑣 − 𝑣𝑠 𝑜𝑏𝑠𝑒𝑟𝑣𝑒𝑑 𝑤𝑎𝑣𝑒𝑙𝑒𝑛𝑔𝑡ℎ 𝜆0 = 𝑓𝑠 Doppler effect equation 𝑣 𝑣𝑓𝑠 𝑓0 = = 𝜆0 𝑣±𝑣𝑠 𝑓0 is observed frequency v is wave speed 𝑓𝑠 is source emitting frequency 𝑣𝑠 is relative speed between source and observer +: moving away relatively; observed frequency decreases -: moving towards relatively; observed frequency increases D C Doppler effect of light Electromagnetic spectrum D C Electromagnetic spectrum Waves that are created as a result of vibrations between an electric field and a magnetic field. Magnetic field and electric field is at right angles. It is transverse wave. Using 3D movies Sun glass Camera Polarisation 1. Only transverse waves can be plane polarised. 2. All types of electromagnetic waves can be plane polarised. 1. Plane polarised 2. Vertical vibrations pass through the slit. The questions What is meaning of polarisation? Why the longitudinal wave can not be polarized? oscillations are in a single Longitudinal waves vibrate direction, which is along the direction of wave perpendicular to the travel, so no matter what the direction of propagation of orientation of the slit, the the wave. waves will be able to get Why the sound wave can not be through. polarized? Sound wave are longitudinal wave. Single and double The magnitude of intensity There is an angle between polarized light and transmission of axis. 𝑎𝑚𝑝𝑙𝑖𝑡𝑢𝑑𝑒 𝑎𝑓𝑡𝑒𝑟 𝑝𝑜𝑙𝑎𝑟𝑖𝑜𝑑 ∶ 𝐴0 𝑐𝑜𝑠𝜃 𝑖𝑛𝑡𝑒𝑛𝑠𝑖𝑡𝑦 𝐼 = 𝑘𝐴2 𝐼0 𝐼 = 𝐴02 (𝐴0𝑐𝑜𝑠𝜃)2 𝐼 = 𝐼0(𝑐𝑜𝑠𝜃)2 Malus’s law The change in intensity against the angle of transmission axis is shown in the graph below Polarized light A polarizer allows a light wave to pass through it if the direction of oscillation of its electric field matches the alignment of the polarizer, and blocks a light wave if the alignment of the polarizer is perpendicular to the direction of oscillation. 1. When the incident light is unpolarized, the intensity (𝐼) of light passing through the polarizer is reduced by a factor of two compared to the intensity (𝐼0) of light entering the polarizer: I0=2I 2. When the incident light is already polarized to begin with, the intensity (𝐼) of light passing through the polarizer is reduced compared to the intensity (𝐼0) of light entering the polarizer according to Malus’s law. B