SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – SPH3U - Unit 4 Waves Chapter 7

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Vibrations A _______ is a disturbance in a ________ created by a series of _________. A medium is any type of material through which a wave may travel (eg: air, metal, glass, etc). ***The medium is the only factor which affects the speed of a wave!*** A vibration is any type of back & forth movement. There are 3 types of vibrations (we will only study the first two)

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Propagation of a Longitudinal Wave

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Propagation of Transverse Waves

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Examples of Vibrations

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Longitudinal vs. Transverse

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Hmmmm… What would a displacement-time graph of a particle experiencing a periodic vibration look like?

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Wave Terminology Amplitude (A) [m] – the maximum displacement of a particle from its rest position during a vibration. Cycle – one complete vibration from rest position to maximum amplitude in both directions and back again. Wavelength (λ) [m] – the distance from one point on a wave to the same point in the next cycle. Distance (d) [m] – the total distance a particle travels during one cycle of a vibration. Period (T) [s] – the time it takes for one cycle of vibration. Frequency (f) [Hz] –the number of cycles completed in one second.

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Example 1.Find the Period of a car running at 3,400 RPM. 2.Find the # of revolutions the engine performs in 3 seconds.

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Practice Problems on Waves and Vibrations Set #1 Pg. 331 #1-4

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Think about it… Consider yourself sitting stopped at a railway crossing. How could you determine the speed of the train if you had a stop watch and knew the length of each railway car?

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – The Universal Wave Equation Let the train’s velocity be v Let the length of one car be λ Let the time it takes for one car to cross your field of view be T

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Example 3. It takes a wave crest 0.225s to travel 3.50m. If the frequency of the source is 1250 Hz, what is its wavelength?

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Practice Problems on Waves and Vibrations Set 2 Pg. 339 #5-9

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Natural Frequency When an object is allowed to vibrate freely, such as a mass on a string (pendulum), it will tend to do so at a specific frequency, called its Natural Frequency. Regardless of the amplitude or phase of the object, the natural frequency will remain the same! (Ex: Try dropping a pendulum from different heights – the frequency remains constant).

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Resonance Imagine pushing a child on a swing. It does not take a large force to make the child swing higher. What is required however is that you push at the RIGHT TIME - meaning, at the same natural frequency as the swing and child. In addition, the pushing cycle must be in phase with that of the child/swing. When transfer of energy through a vibration is occurring from one object to a second object having the same natural frequency, it is called Resonance.

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Phase Two objects can have identical amplitudes, frequencies, and wavelengths, and yet be different because they are never at the same point in their cycles at the same time. The term Phase is used to describe this property. We will use a pendulum as our example… In Phase – when the pendulums are both at rest, or moving in the same direction at the same time. Opposite Phase – when the pendulums are moving in opposite directions, equidistant from their rest positions at the same time.

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Phase IN PHASEOPPOSITE PHASE

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Phase Out-of-phase- when the pendulums have the same amplitude and frequency but are not at the same point at the same time. The difference between the same point in their cycles is referred to as Phase difference.

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Transmission & Reflection Reflection –Fixed end reflections: same speed, inverted, same wavelength and amplitude –Not fixed end reflections: same speed, upright, same wavelength and amplitude Transmission –When a wave travels into a different medium, two waves are formed; a transmitted wave into the new medium and a reflected wave back towards the old medium

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Transmission & Reflection

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Summary W: Wavelength A: Amplitude V: Velocity O: Orientation Reflected Wave Transmitted Wave W A V O Light (fast) -> Heavy (slow) Reflected Wave Transmitted Wave W A V O Heavy (slow) -> Light (fast)

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Wave Interference When multiple waves disturb the same medium simultaneously, the resultant movement of the medium is the combination of the movement caused by each individual waves.

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Principle of Superposition When two or more waves are present simultaneously in the same place, the resultant wave is the sum of the individual waves.

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – The resultant wave is larger than either individual (component) wave. Total constructive interference occurs when the resultant wave’s amplitude is at a maximum.

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – The resultant wave is smaller than either component wave. Total destructive interference occurs when the wave’s amplitude is at a minimum (creates a node).

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Standing Waves When two identical waves travel in opposite directions, a special type of interference pattern emerges.

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Standing Waves At intervals that are a __________________, the wave destructively interferes and creates ______ that never move. Between each node, an _________ vibrates maximally. Since the nodes do not move, the sense of movement of the two component waves is lost which creates a standing wave.

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Example The distance between adjacent nodes in the standing wave pattern produced in a piece of string is 25.0cm. a)What is the wavelength of the wave in the string? b)If the frequency of vibration is 200 Hz, calculate the velocity of the wave.

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Modes of Vibration Fundamental mode is the standing wave pattern for a medium vibrating at its fundamental frequency and displays the fewest number of nodes and antinodes Overtones are multiples of the fundamental frequency which will produce a standing wave pattern in the same medium.

SPH3U – Physics 11 University Preparation – Unit 4 – Waves & Sound Created by: Mr. D. Langlois – GECDSB – Diffraction