Summative assessment task Module 2 Waves, sound and light \( \qquad \) Units 1 to 5 1 Suppose Sam is fishing from the harbour wall. He notices that a wave crest passes him every 8 seconds and that the distance between two wave crests is 3 m . He also notices that seagulls floating on the water surface remain in the same position while the waves are moving forward towards the beach. Sam is not a science student. In your own words, explain to Sam the following concepts by referring to the information he gave you: a) the period of the wave b) calculating the frequency of the wave c) the wavelength of the wave d) the speed of the wave e) water waves appearing to be transverse waves f) why water particles move when a wave passes them. 2 A vibrator in a ripple tank generates waves with a frequency of 10 Hz . a) Explain the term 'frequency'. b) Name the type of wave that the vibrator generates. c) Give the name of another type of wave and explain how it differs from the one you gave as your answer to 2 b ). d) Calculate the wavelength of the waves if the distance between 21 crests

Certainly! Let's break down each part of your assessment task to help you understand the concepts related to waves, sound, and light. --- ## **Question 1** **Sam's Observations:** - **Wave Crest Interval:** A wave crest passes every 8 seconds. - **Distance Between Crests:** 3 meters. - **Seagulls’ Behavior:** They remain stationary while waves move toward the beach. Let's address each part: ### **a) The Period of the Wave** **Definition:** The **period** of a wave is the time it takes for one complete wave cycle to pass a given point. **Explanation for Sam:** Sam notices that a wave crest passes him every 8 seconds. This means it takes 8 seconds for one full wave to go by him. Therefore, the period of the wave is **8 seconds**. ### **b) Calculating the Frequency of the Wave** **Definition:** **Frequency** is the number of wave cycles that pass a point in one second. **Relation to Period:** Frequency (**f**) and period (**T**) are inversely related: \[ f = \frac{1}{T} \] **Calculation:** Given the period \( T = 8 \) seconds, \[ f = \frac{1}{8} = 0.125 \text{ Hz} \] **Explanation for Sam:** A frequency of 0.125 Hz means that 0.125 wave crests pass by every second. In other words, one crest passes every 8 seconds. ### **c) The Wavelength of the Wave** **Definition:** **Wavelength** is the distance between two consecutive crests (or any two corresponding points) of a wave. **Given:** Sam observes the distance between two wave crests is **3 meters**. **Explanation for Sam:** The wavelength of the wave is the distance from one crest to the next, which is **3 meters**. ### **d) The Speed of the Wave** **Definition:** **Wave speed** is how fast the wave travels through the medium. **Formula:** \[ \text{Speed} (\nu) = \text{Wavelength} (\lambda) \times \text{Frequency} (f) \] **Calculation:** Given: - Wavelength \( \lambda = 3 \) meters - Frequency \( f = 0.125 \) Hz \[ \nu = 3 \times 0.125 = 0.375 \text{ meters/second} \] **Explanation for Sam:** The wave travels at a speed of **0.375 meters per second** toward the beach. ### **e) Water Waves Appearing to Be Transverse Waves** **Definition of Transverse Waves:** In transverse waves, the particles of the medium move perpendicular to the direction of wave propagation. **Why Water Waves Seem Transverse:** Even though water waves are actually **surface gravity waves** with both transverse and longitudinal motion, from Sam's observation: - The crests and troughs indicate the upward and downward (transverse) movement. - The seagulls appearing stationary suggest that the primary motion is up and down rather than forward. **Explanation for Sam:** Water waves look like they move up and down as they travel forward. This side-to-side (transverse) movement of water particles makes the waves appear to be transverse waves. ### **f) Why Water Particles Move When a Wave Passes Them** **Explanation:** When a wave passes through water: - **Energy Transfer:** The wave carries energy through the water without permanently moving the water itself. - **Particle Motion:** Water particles move in circular orbits. As a wave crest passes, particles move upwards and forward, then downwards and backward, returning to their original position. **Explanation for Sam:** As waves come by, each water molecule moves in a small circle—up and forward when the crest passes, then down and back—so the particles wiggle without traveling with the wave. --- ## **Question 2** **Given:** A vibrator in a ripple tank generates waves with a frequency of **10 Hz**. ### **a) Explain the Term 'Frequency'** **Definition:** **Frequency** is the number of complete wave cycles that pass a given point in one second. **Explanation:** If a wave has a frequency of 10 Hz, it means **10 wave crests** pass by a stationary point every second. ### **b) Name the Type of Wave that the Vibrator Generates** **Type of Wave:** The vibrator in a ripple tank typically generates **transverse waves**. **Explanation:** In a ripple tank, disturbances create waves where the water surface moves up and down perpendicular to the direction the wave travels, characteristic of transverse waves. ### **c) Name Another Type of Wave and Explain How It Differs from the One in 2b** **Another Type of Wave:** **Longitudinal waves** (e.g., sound waves). **Differences:** - **Particle Movement:** In longitudinal waves, particles of the medium move **parallel** to the direction of wave propagation. - **Medium Compression:** These waves involve compressions and rarefactions. - **Example:** Sound waves traveling through air. **Explanation:** Unlike the transverse waves generated in the ripple tank, longitudinal waves have particles that oscillate back and forth in the same direction the wave is moving, causing areas of compression and expansion. ### **d) Calculate the Wavelength of the Waves if the Distance Between 21 Crests** It seems the question is incomplete, but we'll assume it's asking for the wavelength based on the distance between multiple crests. **Assumption:** Let's assume that the total distance spanned by 21 crests corresponds to 20 wavelengths (since wavelength is the distance between two consecutive crests). **Formula:** \[ \lambda = \frac{\text{Total Distance}}{\text{Number of Wavelengths}} \] **Given:** If the distance between 21 crests is, for example, 60 meters (you can replace this with the actual distance if provided). **Calculation:** Number of wavelengths = Number of crests - 1 = 21 - 1 = 20 \[ \lambda = \frac{60 \text{ meters}}{20} = 3 \text{ meters} \] **Explanation for Sam:** If 21 wave crests stretch over 60 meters, then each wavelength (the distance between two crests) is **3 meters**. *(Please ensure to use the actual distance provided in your question for an accurate calculation.)* --- I hope this helps clarify the concepts for you! If you have any more questions or need further explanations, feel free to ask.