Lower Secondary Science Waves: Step-by-Step Worked Examples

Quick answer

Feeling like your heart sinks when you see wave questions in your exams? Don't worry, you're not alone. Today, we'll break down wave-related questions step by step, so by the end of this, you'll understand not just what to do, but why you're doing it. Once this clicks, the rest is easier!

“Stuck on a question? See simple explanations that help you understand fast.”
👉 Give it a try and turn confusion into clarity in minutes.

What you need to know

Waves are disturbances that transfer energy from one place to another without transferring matter. Imagine waves at East Coast Park — the water moves up and down, but it doesn't actually travel towards you. This is how waves work!

“Access more than 1000+ past year papers to practice”
👉 Start a paper today and test yourself like it’s the real exam.

Understanding Waves

Parts of a Wave

To tackle wave questions, you need to understand the basic parts of a wave:

• Crest: The highest point of a wave.
• Trough: The lowest point.
• Amplitude: Distance from the rest position to the crest.
• Wavelength: Distance between two consecutive crests or troughs.
• Frequency: How many waves pass a point in one second.

Types of Waves

There are two main types of waves you should know:

• Transverse Waves: Waves where particles move perpendicular to the direction of energy transfer. Think of shaking a rope up and down.
• Longitudinal Waves: Waves where particles move parallel to the direction of energy transfer, like sound waves. Imagine pushing and pulling a slinky.

Common mistakes students make

One mistake I repeatedly see among my Sec 4 students is memorizing keywords like "crest" or "frequency" without understanding what they mean. This often leads to panic when the question looks different from tutorial examples. Remember, the examiner is testing whether you truly understand the process.

How to fix these mistakes:

• Visualize the Wave: Draw a simple wave diagram to identify parts like crests and troughs.
• Focus on Understanding: Don't just memorize definitions. Try to explain concepts in your own words.
• Practice Different Questions: Expose yourself to various types of questions. This will help you recognize patterns and apply concepts flexibly.

Exam tip

Be precise in your answers. In O-Level questions, precision matters more than length. Instead of writing everything you know about waves, focus on what the question is specifically asking. Remember, quality over quantity!

Worked examples

Question 1

A wave has a frequency of 5 Hz and a wavelength of 2 meters. Calculate the speed of the wave.

Solution

Step 1: Use the wave speed formula: $𝑣 = 𝑓 \times \lambda$
Why: This formula ties together speed (𝑣), frequency (𝑓), and wavelength ($\lambda$) — it's the key to finding wave speed.

Step 2: Substitute the given values: $𝑣 = 5 \times 2$
Why: You're plugging in the frequency (5 Hz) and wavelength (2 m) to find the speed.

Step 3: Calculate: $𝑣 = 10 \text{ m/s}$
Why: This is the final speed of the wave, showing how fast energy travels through the medium.

Question 2

A wave travels through water with a speed of 12 m/s and a frequency of 3 Hz. What is its wavelength?

Solution

Step 1: Use the wave speed formula again: $𝑣 = 𝑓 \times \lambda$
Why: This formula is your go-to for relating speed, frequency, and wavelength.

Step 2: Rearrange to find wavelength: $\lambda = \frac{𝑣}{𝑓}$
Why: You need to isolate $\lambda$ to find the wavelength.

Step 3: Substitute values: $\lambda = \frac{12}{3}$
Why: Insert the speed (12 m/s) and frequency (3 Hz) into the formula.

Step 4: Calculate: $\lambda = 4 \text{ m}$
Why: This gives you the distance between wave crests.

Question 3

If a wave has an amplitude of 3 cm and a wavelength of 6 cm, describe a transverse wave motion.

Solution

“Doing Secondary Science? Pick a topic and practise like it’s a real exam — with clear answers right after.”
👉 Try Tutorly now and start a Science topic in seconds.


Step 1: Define transverse wave: Particles move perpendicular to wave direction.
Why: It's important to understand particle motion to describe wave behavior.

Step 2: Use given amplitude: Particles move up and down by 3 cm.
Why: Amplitude shows the maximum displacement from rest position.

Step 3: Mention wavelength: Wave repeats every 6 cm.
Why: Wavelength tells you how often the wave shape repeats.

Question 4

Explain how sound waves differ from light waves.

Solution

Step 1: Identify sound waves as longitudinal.
Why: Sound waves require a medium and involve compressions and rarefactions.

Step 2: Identify light waves as transverse.
Why: Light waves can travel through a vacuum and don't need a medium.

Step 3: Compare speed: Light travels faster than sound.
Why: Understanding the speed difference helps explain phenomena like seeing lightning before hearing thunder.

Quick summary

• Waves transfer energy, not matter.
• Key parts: crest, trough, amplitude, wavelength, frequency.
• Transverse vs. longitudinal waves: particle motion differs.
• Use $𝑣 = 𝑓 \times \lambda$ to calculate wave speed.
• Be precise in exams; focus on what's asked.

FAQ

Q 1: What is the difference between frequency and wavelength?
Frequency is how often a wave passes a point in a second. Wavelength is the distance between two consecutive crests or troughs.

Q 2: How does amplitude affect a wave?
Amplitude affects the wave's energy. Higher amplitude means more energy and greater displacement from the rest position.

Q 3: Can sound travel in a vacuum?
No, sound needs a medium like air or water to travel. That's why you can't hear anything in space!

Q 4: Why do we see lightning before we hear thunder?
Light travels faster than sound. So, during a storm, we see the lightning before the sound waves of thunder reach us.

Related Topics You Should Learn Next

• Lower Secondary Science: Waves Explained Simply for Singapore Students
• Lower Secondary Science Waves: The Complete Guide for Singapore Students
• How To Write An Effective Tuition Advertisement In Singapore (Without Sounding Cringe)
• Lower Secondary Science Waves Guide

“Practice PSLE Science questions and get clear, step-by-step answers instantly.”
👉 Try a question now and see how fast you can improve.