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PHYSICS, M3 EQ-Bank 10 MC

Which of the following waves has the shortest wavelength?

  1. A microwave with a frequency of \(3.0 \times 10^{11}\ \text{Hz}\).
  2. A sound wave with a frequency of \(15\ \text{kHz}\).
  3. A water wave travelling at \(4.0\ \text{ms}^{-1}\) with a frequency of \(0.25\ \text{Hz}\).
  4. A radio wave with a frequency of \(90\ \text{MHz}\).
Show Answers Only

\(A\)

Show Worked Solution

\(v=f\lambda\) \(\Rightarrow\) \(\lambda = \dfrac{v}{f}\).

  Microwave: \(\lambda = \dfrac{3.0 \times 10^8}{3.0 \times 10^{11}} = 1 \times 10^{-3}\ \text{m}\).

  Sound wave: \(\lambda = \dfrac{340}{15 \times 10^3} = 0.023\ \text{m}\).

  Water wave: \(\lambda = \dfrac{4.0}{0.25} = 1\ \text{m}\).

  Radio wave: \(\lambda = \dfrac{3.0 \times 10^8}{90 \times 10^6} = 3.33\ \text{m}\).
 

  • The microwave has the smallest wavelength.

\(\Rightarrow A\)

PHYSICS, M3 EQ-Bank 3

How do mechanical waves differ from electromagnetic waves? Include examples to illustrate your response.   (4 marks)

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  • Mechanical waves (e.g. sound, water waves, vibrations on a string) need a medium to travel through.
  • They transfer energy by making particles in the medium vibrate. This vibration can be either perpendicular (transverse waves – eg. ripples in water) or parallel (longitudinal waves – eg. sound waves in air) to the direction of motion.
  • The speed of a mechanical wave depends on the medium’s physical properties.
  • Electromagnetic waves (e.g. light, radio waves, X-rays) do not need a medium and can move through a vacuum.
  • These waves are transverse, made of electric and magnetic fields oscillating at right angles.
  • They travel fastest in a vacuum \((3 \times 10^8\ \text{ms}^{-1})\) and slow down in materials like air or glass—how much depends on the material’s refractive index.
  • The electromagnetic spectrum includes a wide range, from low-frequency radio waves to high-frequency gamma rays.
Show Worked Solution
  • Mechanical waves (e.g. sound, water waves, vibrations on a string) need a medium to travel through.
  • They transfer energy by making particles in the medium vibrate. This vibration can be either perpendicular (transverse waves – eg. ripples in water) or parallel (longitudinal waves – eg. sound waves in air) to the direction of motion.
  • The speed of a mechanical wave depends on the medium’s physical properties.
  • Electromagnetic waves (e.g. light, radio waves, X-rays) do not need a medium and can move through a vacuum.
  • These waves are transverse, made of electric and magnetic fields oscillating at right angles.
  • They travel fastest in a vacuum \((3 \times 10^8\ \text{ms}^{-1})\) and slow down in materials like air or glass—how much depends on the material’s refractive index.
  • The electromagnetic spectrum includes a wide range, from low-frequency radio waves to high-frequency gamma rays.