AQA GCSE Measuring the speed of sound waves in air

AQA GCSE Measuring the speed of sound in air(Physics)

Measuring the speed of sound in air.

There are several ways to measure the speed of sound in air

Person hitting an object, another person timing.

1.Two people will stand a distance of about 200-300m apart. The exact distance needs to be measured.

2. The man in this case will strike the drum to make a sound.

3.The woman with the stopwatch will start the stopwatch when she sees the drumstick hit the drum and stop the stopwatch when she hears the sound.

4. This will record the time taken for the sound wave to travel from the drum to the woman.

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.

Rebound method

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

2. The person will then clap and listen for the echo.

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

4. Another person will then start a stopwatch when they hear a clap and then stop the stopwatch after 30 claps.

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 = 1500m/4.41 seconds = 340m/s

Using an oscilloscope

An oscilloscope is set up with two microphones. Each microphone will detect sound, sending a signal to the oscilloscope. The oscilloscope shows two sound waves, one for each microphone.

When a sound at a constant known frequency is generated and the microphones next to each other two sound waves are seen, but the waves are not aligned.

The distance between the microphones is increased until the two waves directly align as shown in the oscilloscope below. The distance between the two microphones is exactly 1 wavelength. This distance is measured with a ruler or meter rule.

The frequency of the sound wave was known, we previously measured the wavelength. To, calculate the wave speed we use the following formula

Wave speed,v = Wavelength, λ x frequency,f

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.

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.

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.