Practice Question

1.Arnold and Marie were asked by their teacher to measure the speed of sound in air using a stopwatch and a pair of cymbals. Write a method to explain how to do this.

1.Arnold and Marie will stand a distance of about 200-300m apart. The exact distance needs to be measured.

2. One of them will strike the cymbals to make a sound.

3.The other person withth the stopwatch will start the stopwatch when they see the cymbals hit each other and stop the stopwatch when they hear the sound. 

4. This will record the time taken for the sound wave to travel from the cymbals to the other person.

5. This process will be repeated several times and a mean calculated. Repeating the data will make it more reliable!

Then use the following formula. 

Speed = distance/time

2. Arnold and Marie didn’t obtain and accurate value for the speed of sound in air, so their teacher suggested they tried using the cymbals near the school wall. Write a method for this. 

1.One person with cymbals will stand 25m from a wall. This distance needs to be measured, using a meter rule, or trundle wheel.

2. The person will hit the cymbals and listen for the echo. 

3. Once the echo is heard, the person will hit the cymbals to the rhythm of the echo.

4. Another person will then start a stopwatch when they hear the cymbals hit and then stop the stopwatch after 30 hits.

5. Each sound wave travels 2 x 25m, so 50m in total. 

6. As there are 30 claps, the total distance travelled is 50m x 30 = 1500m

7. The other person recorded a time period of 4.41 seconds for the 30 claps

8. Use the  following formula

Speed = distance/time

3. Arnold’s teacher set up a class demonstration using two microphones and an oscilloscope to measure the speed of sound. Write a method to explain how this can be carried out. 

Two microphones connected to a oscilloscope are used. Sound wave of known frequency is detected by the microphones. 

The microphones are moved apart until the sound waves match on the oscilloscope screen. Distance between the microphones is the wavelength of sound wave. Frequency of sound wave is known.

Wave speed = wavelength x frequency.