Physics Unit 3

SAC1: Summary report of sound practical activities

The report will consist of several short tasks done under test conditions. Each task will assess the knowledge acquired and skills developed by particular practical activities relevant to the area of study Sound and Outcome 1. The student’s practical work log book may be used as a reference during the SAC and the full functions of a graphing calculator may be used. Any graphs that are part of a task may be plotted on graph paper, or in a graphics calculator and printed in the classroom during the task.

2. The log book is to be submitted with the completed task.

3. No text book or photocopied material from a text book may be used.

Name …………………………. Number ………………………

Time: 60 min

Answer in the spaces on this question sheetScore / 61

  1. The diagram below shows an activity that demonstrates how sound is produced.

Describe the next step in this activity and the inferences that could be made about the production of sound. [4]

  1. Two activities that demonstrate how sound is transmitted are
  • Observing the movement of a candle flame in front of a speaker
  • Sending longitudinal waves along a stretched slinky spring

For each activity describe the observations that could be made by a student and the inferences that could be drawn about the transmission of sound. [8]

  1. Calculate the period and frequency of the sounds shown in the following diagrams of CRO screens. Taking the speed of sound in air as 350m/s also calculate the wavelength of each sound. The scale marks may be taken as 1 cm apart.

a)

b)

c)

d) Which of these sounds would be above or below the normal range of human hearing? Give reasons for your choices. [4]

e) If you could hear the sounds, which would be loudest? Explain your choice. [3]

  1. A new technology room is being built at your school. The room will have several power tools and some metal working equipment and is close to some year 8 classrooms. The Physics class is preparing some advice about preventing the noise from the technology classes affecting lessons in these rooms.

a)What would be a safe level of sound in a classroom where students work for 5 or 6 hours each day? [2]

b)You visit a school with a technology room similar to the one proposed for your school and use sound level meters to measure the sound levels inside and outside the room when the tools and machinery are operating. What scale would you choose on the sound level meters? Give a reason for your choice. [2]

c)Inside the room the measurements were 92dB, 95dB and 98dB. One student says that these readings show that the intensity doubled between the first and second reading and again between the second and third reading. Another student disagrees and says the readings are only 3 dB apart each time so cannot be doubling. Which student is right? Give reasons for your answer. [4]

d)What would be your advice about the need for hearing protection in this room? [3]

5. The class now measures sound levels outside the technology room.The readings they obtained are given in the following table.

Distance from the door of the room (m) / Intensity of sound (W/m2) / Sound level (dB)
0m / 90
1m / 88
2m / 82
3m / 78
4m / 76

a) Calculate the intensity for each sound level measurement and enter it in the table. [4]

b) Plot a graph of sound intensity against distance from the room using the graph paper supplied. [4]

c) From the shape of this graph what is a likely relationship between sound intensity and distance from the source of sound? [3]

If the shape of the graph did not match the theoretical relationship between sound intensity and distance from the source of sound, describe two possible causes for this difference. [2]

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