Physics A Level (Waves)

might be hell at first, get A

Describe how ultrasound travels through a metal. (3 marks)

• The ultrasound wave makes the metal ions vibrate due to the high frequencies.

• The ultrasound travels as a longitudinal wave into the metal, which means it creates alternating compressions and rarefactions.

• Since it is a longitudinal wave, the metal ions are vibrating parallel to the direction of energy transfer.

Explain why pulses are used rather than a continuous wave and how the duration of the pulse affects the thickness of the pipe wall that can be accurately measured? (3 marks)

• Pulses can return which means you must measure the time taken for it to return.

• The echo must be clear which means the pulse must return before one is emitted.

• If the pulse duration is long, the thickness is large, if the pulse duration is short, the thickness is small.

How does ultrasound travel through water. (2 marks)

• The water particles move in parallel to the direction of energy transfer.

• As this happens, there will be alternating compressions and rarefactions.

Bat use ultrasound in air when hunting prey. Explain whether bats or dolphins would be able to locate their prey more precisely. (3 marks)

• Speed of sound in air is slower than the speed of sound in water, due to the relative distance between each particle.

• Since the speed of sound in water is lower, so is the wavelength according to the formula, wave speed = f x λ.

• The bats would have a greater resolution since there is a short wavelength.

Explain how sound can cause a piezoelectric film to generate a potential difference. (4 marks)

• The sound waves travel as a longitudinal wave.

• This means that the sound wave will vibrate the particles on the piezoelectric film, creating a force.

• This force will cause a potential difference.

• There will be a series of compressions and rarefactions.