A motorway passes close to a row of homes. Fig. 1 shows a proposed noise barrier placed between the road and one garden. Engineers compare a thin wooden fen...
Question 1 Report
A motorway passes close to a row of homes. Fig. 1 shows a proposed noise barrier placed between the road and one garden. Engineers compare a thin wooden fence with a taller barrier made from dense concrete. Sound from car engines, tyres and horns can travel over or around a barrier. The homes are 40 m from the road. The engineers want a design that reduces the sound energy reaching the garden without blocking the drivers' view at a junction. The diagram shows the direct path and a possible diffracted path of sound waves.
(a) Give one source of sound from the motorway. [1]
(b) Explain why a taller barrier can make the garden quieter. [2]
(c) Which material, wood or dense concrete, should be chosen for the barrier? [1]
(d) Describe what happens to the sound energy when it reaches the concrete. [1]
The diagram shows a microphone connected by a cable to an oscilloscope during a school sound investigation. A pupil speaks the same word at a quiet and then a louder level, standing 1.0 m from the microphone. Two traces are displayed. Each horizontal division represents 1 ms. The potential difference from the microphone changes because its diaphragm vibrates. Trace A has a smaller vertical height than trace B, while the spacing of their peaks is the same. The pupil uses the figure to compare loudness without changing the sound source.
(a) Name the component that changes sound vibrations into an electrical signal. [1]
(b) What feature of trace B shows that the sound is louder? [1]
(c) Explain why both traces have the same pitch. [2]
(d) Give the unit used for the time scale on this oscilloscope. [1]
Answer Details
Motorway noise barrier
(a) One source of sound is an engine. [1] Tyres on the road or a horn are also acceptable.
(b) A taller barrier blocks more of the direct sound path from the road to the garden. [1] Less sound can diffract, or travel, over the top of the barrier to reach the garden. [1]
(c) Dense concrete should be chosen. [1] Its greater density makes it more effective than a thin wooden fence for reducing transmitted sound.
(d) When sound reaches the concrete, some sound energy is reflected and some is absorbed, transferring energy to internal energy in the barrier. [1]
Microphone and oscilloscope
(a) The microphone changes sound vibrations into an electrical signal. [1]
(b) Trace B has a greater amplitude, shown by its taller vertical height. [1] Greater amplitude corresponds to a louder sound.
(c) The traces have the same period, shown by identical spacing between corresponding peaks. [1] Since \(f=\frac{1}{T}\), equal periods mean equal frequencies, so they have the same pitch. [1]
(d) The time scale is measured in milliseconds, ms. [1]
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