Lesson Notes By Weeks and Term v4 - SHS 2
WAVES
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WAVES
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Subject: Physics
Class: SHS 2
Term: 1st Term
Week: 17
Grade code: 2.2.2.LI.3
Strand code: 2
Sub-strand code: 2
Content standard code: 2.2.2.CS.1
Indicator code: 2.2.2.LI.3
Theme: ENERGY
Subtheme: WAVES
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Waves are all around us, carrying energy from one place to another without transferring matter. In Ghana, we experience waves every day. When we listen to Highlife music on the radio (like on Peace FM or Joy FM), we are receiving radio waves. The beautiful sea waves at Labadi or Cape Coast are water waves carrying energy from the ocean. Even the light from the sun that helps our cocoa grow is a form of wave. This lesson focuses on understanding the fundamental properties of a simple, repeating wave, often called a sinusoidal wave. By learning to describe and measure these properties, we can understand how different waves behave and how we use them in technology and daily life.
A. Visualising a Wave
Imagine you and a friend are holding a long rope. If you shake your end up and down in a regular rhythm, you create a wave that travels along the rope. This is a transverse wave, where the particles of the rope move perpendicular (up and down) to the direction the wave energy is travelling (along the rope). A perfect, smooth wave of this type is called a sinusoidal wave.
We can represent this wave using two types of graphs: Displacement-Distance Graph: A "snapshot" of the entire wave at one specific moment in time. It shows the displacement of every particle along the rope at that instant. Displacement-Time Graph: This graph focuses on just ONE particle on the rope and tracks its displacement (how far it moves up and down) over a period of time. B. Key Wave Properties
Let's define the essential properties using our graphs. Amplitude (A) Definition: The maximum displacement or distance moved by a point on a vibrating body or wave measured from its equilibrium position. Explanation: It's simply "how high" the wave goes from the middle line. A wave with a large amplitude carries more energy. Think of a loud sound (high amplitude) versus a quiet sound (low amplitude). Unit: Metres (m). How to find it: On either graph, it is the distance from the central axis (equilibrium position) to the top of a crest or the bottom of a trough. Wavelength (λ) Definition: The distance between two successive crests or troughs of a wave. It is the length of one complete wave cycle. Explanation: `λ` is the Greek letter "lambda". It tells you how "long" the wave is in space. Unit: Metres (m). How to find it: Only on a Displacement-Distance graph. Measure the distance along the x-axis for one full cycle (e.g., from one peak to the next peak). Period (T) Definition: The time taken to complete one full oscillation or cycle. Explanation: It tells you how "long" the wave takes in time to complete a cycle. If a wave at the beach hits the shore every 5 seconds, its period is 5 s. Unit: Seconds (s). How to find it: Only on a Displacement-Time graph. Measure the time along the x-axis for one full cycle. Frequency (f) Definition: The number of complete cycles or oscillations that occur per second. Explanation: Frequency tells you "how often" a wave cycle happens. If you shake the rope up and down 3 times every second, the frequency is 3 cycles per second. Unit: Hertz (Hz). 1 Hz = 1 cycle per second. Relationship with Period: Frequency and Period are inverses of each other. A long period means a low frequency, and a short period means a high frequency. > Formula: `f = 1 / T` Wave Velocity or Speed (v) Definition: The speed at which the wave energy travels through the medium. Explanation: This is how fast the wave moves from one point to another. C. The Wave Equation (Collaborative Derivation)