Waves are disturbances that transfer energy from one place to another without transporting matter. In the IGCSE Physics syllabus, we explore waves through everyday examples such as vibrating ropes, springs, and water waves. Understanding how these waves behave will help you answer exam questions about amplitude, wavelength, frequency, speed, and more.
A wave can be either transverse (particles move perpendicular to the direction of travel) or longitudinal (particles move parallel to the direction of travel). Think of a guitar string vibrating up and down (transverse) versus a slinky compressing and expanding (longitudinal).
When you pluck a rope or a spring, you create a disturbance that travels along the material. The rope’s particles move perpendicular to the wave’s direction, while the spring’s particles move back and forth along the spring’s axis.
Key points:
The mathematical description of a simple transverse wave is:
\$y(x,t) = A \sin(kx - \omega t)\$
Where \$k = 2\pi/\lambda\$ is the wave number and \$\omega = 2\pi f\$ is the angular frequency.
Drop a stone into a calm pond and observe the ripples. These are transverse waves on the surface of the water. The same principles apply: amplitude, wavelength, frequency, and speed can be measured. In the lab, you can use a ripple tank to create controlled water waves and study how they interact.
| Property | Definition | Example |
|---|---|---|
| Amplitude \$A\$ | Maximum displacement from equilibrium. | Height of a wave crest. |
| Wavelength \$\lambda\$ | Distance between successive crests. | Length of one full wave on a rope. |
| Frequency \$f\$ | Cycles per second (Hz). | How many times a wave passes a point each second. |
| Period \$T\$ | Time for one complete cycle. | \$T = 1/f\$. |
| Speed \$v\$ | Distance travelled per unit time. | \$v = f\lambda\$. |
| Phase | Relative position of a point on the wave. | Used to describe wave interference. |
Analogy: Imagine a line of people holding hands. If the first person lifts their hand (a disturbance), the motion travels along the line like a wave. The height of the hand lift is the amplitude, and the distance between two people who lift their hands at the same time is the wavelength.
Example: A rope 2 m long is fixed at one end. If a wave with a wavelength of 0.5 m travels along it, the wave speed is \$v = f\lambda\$. If the frequency is 4 Hz, then \$v = 4 \times 0.5 = 2\$ m s⁻¹.
Tip 1: Always state the formula you are using before plugging in numbers. For example, write \$v = f\lambda\$ before calculating the speed.
Tip 2: When asked to compare two waves, look at their amplitudes, wavelengths, and frequencies. A wave with a larger amplitude carries more energy.
Tip 3: Remember that the period \$T\$ is the reciprocal of the frequency: \$T = 1/f\$. This is useful when converting between \$f\$ and \$T\$ in questions.
Tip 4: Use diagrams to show wave direction and key points (crest, trough, equilibrium). A clear sketch can earn extra marks.
Tip 5: For wave speed questions, check if the medium’s properties (e.g., tension in a rope, density of water) are given; they may affect the speed.
Waves transfer energy without moving matter. Key properties—amplitude, wavelength, frequency, period, speed, and phase—describe a wave’s behaviour. By practising with ropes, springs, and water waves, you’ll master the concepts needed for the IGCSE Physics exam.