GENERAL PROPERTIES OF WAVES INTRODUCTION TO WAVES Mr Elijah Ong

Tsunami Mr Elijah Ong

Uses of waves What are some examples or applications of waves in everyday life? Hydropower Guitar/piano, in fact all musical instruments The above are mechanical waves Some electromagnetic waves includes light, radio waves, x-rays Mr Elijah Ong

Kallang Waves! Mr Elijah Ong

What is a wave? Spreading of disturbance from one place to another. The source is a vibration or oscillation. Energy is transferred from one point to another WITHOUT physical transfer of any material between the two points Mr Elijah Ong

Demo WAVES Slinky or ropes Transverse waves http://www.ngsir.netfirms.com/englishhtm/TwaveA.htm Mr Elijah Ong

Transverse Waves Transverse waves travel in a direction PERPENDICULAR to the direction of the vibrations. Mr Elijah Ong

Mr Elijah Ong

Transverse Waves Some Examples: water waves rope waves electromagnetic waves (example: light) Mr Elijah Ong

The Slinky Coil What do you notice about the direction of the vibrations and the direction of the wave? Mr Elijah Ong

The other type of wave called… … Longitudinal Wave… What is a longitudinal wave? A wave where the direction of travel is parallel to the direction of vibration. Mr Elijah Ong

How does it look like? Demonstration of a longitudinal wave? Slinky Coil On an Applet Mr Elijah Ong

Longitudinal Waves Compression Rarefaction Places where air pressure is slightly higher than the surrounding air pressure. Rarefaction Places where air pressure is slightly lower than the surrounding air pressure. Mr Elijah Ong

Longitudinal Waves Examples - Sound waves Mr Elijah Ong

LONGITUDINAL WAVES Longitudinal waves travel in a direction PARALLEL to the direction of vibrations. We use compressions and rarefactions to describe them Compression Rarefactions Mr Elijah Ong

Demo on applet http://www.ngsir.netfirms.com/englishhtm/Lwave.htm Mr Elijah Ong

Example Q. A sound wave in air has a frequency of 262Hz and travels with a speed of 343m/s. How far apart are the wave compressions? A. Given f = 262 Hz and v = 343m/s, Distance between wave compression = wavelength = v / f = 1.3m (1 dp) Mr Elijah Ong

Wavefront That is a… wavefront - an imaginary line on a wave that joins all points which have the same phase of vibration. Mr Elijah Ong

Crests and Troughs Crests: points of maximum displacement on a wave Troughs: points of minimum displacement on a wave displacement CREST Distance along rope TROUGH Mr Elijah Ong

AMPLITUDE (A) Maximum Displacement from the rest or central position. SI unit metre (m) displacement crest crest amplitude distance along rope amplitude trough Mr Elijah Ong

Wavelength (λ) The distance between two successive points of the same phase. Example: distance between two crests. SI unit: metre (m). displacement Wavelength crest λ crest amplitude position along rope amplitude trough Mr Elijah Ong

Frequency (f) Number of complete waves generated per second (or number of cycles/oscillations per second) SI unit: hertz (Hz) E.g: 5 Hz mean 5 waves generated in 1s Mr Elijah Ong

Period (T) Time taken to generate one complete wave (or to complete one cycle) SI unit: second (s) E.g. 5 Hz mean 5 waves generated in 1s 1 wave is generated in 1/5 = 0.25 s Therefore, Period (T) = 0.25s Mr Elijah Ong

Relationship between T and f As f increases, T decreases Mr Elijah Ong

How fast is the wave moving? Mr Elijah Ong

Find the velocity of waves Velocity of wave is the product of its frequency and wavelength Mr Elijah Ong

Example Q. A fisherman notices that wave crests pass the bow of his anchored boat every 3.0s. He measures the distance between two successive crests to be 6.5m. How fast are the waves travelling? A. From the question, we know the period, T = 3.0s, and the wavelength is 6.5m. Therefore, wave speed, v = 6.5 / 3 = 2.2ms-1 (1 dp) Mr Elijah Ong

Using the 2 formulas, can you combine them and formed a third equation? Mr Elijah Ong

2 types of graphs to note! The displacement-position graph Able to find wavelength Amplitude The displacement-graph Period Mr Elijah Ong

Displacement-time graph Distance between two crests denotes the period in a displacement-time graph.( Contrast this with the displacement-position graph! What is the difference?) displacement Period crest T crest amplitude time amplitude trough Mr Elijah Ong

Displacement-time and displacement-position graphs Displacement-time graph： Shows the displacement of ONE particle (from the rest position) at different times. ONE at different times Displacement-position graph： Shows the displacement of ALL particles at a certain time. ALL at a certain time Mr Elijah Ong

Try this Textbook page 177 Mr Elijah Ong

Question Particles in the medium vibrate when the wave passes by. In which direction does the particle move? motion of wave wave at next moment ? ? wave at this moment Mr Elijah Ong

Question In which direction does particle a move? ? ? motion of wave wave at this moment ? wave at next moment Downwards. To the right. Other： _______ Mr Elijah Ong

Vibration vs Waves Vibrations simply refers to one single particle vibrating at its mean position Waves refer to the all the particles’ vibrations with respect to time They are essentially different! Don’t mix these two terms up. Mr Elijah Ong

SUMMARY Mr Elijah Ong