Question 1

What is the difference between transverse and longitudinal waves?

Accepted Answer

In transverse waves, the oscillations (vibrations) are perpendicular to the direction of energy transfer. Examples include light, water waves, and all electromagnetic waves. In longitudinal waves, the oscillations are parallel to the direction of energy transfer, creating compressions (where particles are close together) and rarefactions (where they are spread out). Sound waves are a classic example of longitudinal waves.

Question 2

How do I calculate wave speed using the wave equation?

Accepted Answer

The wave equation is v = f × λ, where v is wave speed in metres per second (m/s), f is frequency in hertz (Hz), and λ is wavelength in metres (m). To calculate wave speed, multiply the frequency by the wavelength. For example, if a wave has a frequency of 50 Hz and a wavelength of 2 m, its speed is 50 × 2 = 100 m/s. You can rearrange the equation to find frequency (f = v ÷ λ) or wavelength (λ = v ÷ f).

Question 3

Why do we use different types of electromagnetic waves for different purposes?

Accepted Answer

Different electromagnetic waves have different wavelengths and frequencies, which affect their properties. For example, radio waves have long wavelengths that can diffract around obstacles, making them ideal for broadcasting. Microwaves are absorbed by water molecules, so they are used for cooking and satellite communication. X-rays have high energy and can penetrate soft tissue, making them useful for medical imaging. The choice depends on the specific interaction with matter needed.

Question 4

What is the difference between reflection, refraction, and diffraction?

Accepted Answer

Reflection occurs when a wave bounces off a surface, following the law of reflection (angle of incidence equals angle of reflection). Refraction is the change in direction of a wave as it passes from one medium to another due to a change in speed. Diffraction is the spreading out of waves when they pass through a gap or around an obstacle. The amount of diffraction depends on the size of the gap relative to the wavelength – more diffraction occurs when the gap is similar in size to the wavelength.

Question 5

How does sound travel through different mediums?

Accepted Answer

Sound waves are longitudinal and require a medium (solid, liquid, or gas) to travel. They travel fastest in solids because particles are closely packed, allowing vibrations to transfer quickly. In liquids, speed is slower, and in gases, it is slowest because particles are far apart. Sound cannot travel through a vacuum because there are no particles to vibrate. The speed of sound in air at room temperature is approximately 340 m/s.

Question 6

What are the dangers of electromagnetic waves?

Accepted Answer

The dangers depend on the energy of the waves. High-frequency waves like ultraviolet (UV), X-rays, and gamma rays are ionising – they have enough energy to remove electrons from atoms, which can damage cells and DNA, leading to cancer or mutations. UV from the sun can cause skin cancer and eye damage. X-rays and gamma rays are used in medicine but require shielding. Lower-frequency waves like radio and microwaves are non-ionising but can cause heating effects (e.g., microwave ovens).

Topic 4 – Waves

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Related Topics in EDEXCEL GCSE Physics

Topic 1 – Key concepts of physics

Topic 10 – Electricity and circuits

Topic 11 – Static electricity

Topic 12 – Magnetism and the motor effect

How to Revise Topic 4 – Waves — Edexcel GCSE Physics

Examiner Tips for Topic 4 – Waves

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