OxfordAQA International GCSE Physics 3.3 Waves Exam Questions

About OxfordAQA International GCSE Physics 3.3 Waves

Waves in OxfordAQA International GCSE Physics covers how waves transfer energy and information without transferring matter. You learn transverse and longitudinal waves, frequency, wavelength, amplitude and the wave equation, then the electromagnetic spectrum with its uses and hazards, including X-rays in medicine. Sound, echoes and reflection by plane mirrors apply to all students. The separate Physics course adds ultrasound, refraction calculations with refractive index, total internal reflection and optical fibres, and lenses and the eye. Examiners regularly ask for v = f x lambda calculations, the order of the electromagnetic spectrum, ray diagrams and explanations of why waves refract at a boundary.

What you need to know

• Wave basics Transverse waves oscillate perpendicular to the direction of energy transfer (electromagnetic and water waves); longitudinal waves oscillate parallel to it, with compressions and rarefactions (sound). Learn amplitude, wavelength, frequency, period and wavefront. v = f x lambda.
• Wave behaviour At a boundary waves can be reflected, transmitted or absorbed. Waves refract when their speed changes, and diffract through gaps or round edges; diffraction is greatest when the gap is similar in size to the wavelength.
• Electromagnetic spectrum In order of increasing frequency: radio, microwaves, infrared, visible light, ultraviolet, X-rays, gamma. All travel at the same speed in a vacuum. Uses include TV and Bluetooth (radio), mobile phones and satellite TV (microwaves), remote controls (infrared), fibre optics (light), security marking (UV), medical imaging (X-rays) and sterilising (gamma).
• Hazards and infrared Microwaves heat tissue, infrared burns skin, UV causes skin cancer and blindness, X-rays and gamma damage cells and cause mutations. Dark matt surfaces are good absorbers and emitters of infrared; light shiny surfaces are poor absorbers and good reflectors.
• Sound and ultrasound Humans hear about 20 Hz to 20 000 Hz. Pitch depends on frequency and loudness on amplitude. Ultrasound (separate Physics) is above 20 000 Hz, partly reflects at boundaries and is used for prenatal scans and breaking kidney stones; distance = speed x time, halving for an echo.
• Reflection Angle of incidence = angle of reflection, measured from the normal. A plane mirror image is virtual, upright and laterally inverted.
• Refraction and TIR (separate Physics) Light bends towards the normal entering a denser medium and away from it leaving. n = sin i / sin r and sin c = 1 / n. Total internal reflection happens when the angle of incidence in the denser medium is greater than the critical angle, and is used in optical fibres. Required practical: investigate refraction of light by different substances.
• Lenses (separate Physics) Converging and diverging lenses form images that can be described as real or virtual, upright or inverted, magnified or diminished. Magnification = image height / object height.

Common mistakes in 3.3 Waves

• Measuring the angle of incidence from the surface. Angles are always measured from the normal.
• Saying sound travels as a transverse wave or through a vacuum. Sound is longitudinal and needs a medium.
• Forgetting to halve the time in echo questions. The wave travels to the boundary and back.
• Saying light refracts because it changes direction. It refracts because its speed changes; the direction changes unless it meets the boundary along the normal.
• Mixing up the order of the electromagnetic spectrum. Learn a mnemonic, and remember wavelength decreases as frequency and energy increase from radio to gamma.

Try three 3.3 Waves exam-style questions