Wave Practials

• Measuring the speed of sound with direct measurement:

  1. 2 people stand 100m apart.
  2. 1 person claps 2 bricks.
  3. The other person uses a stopwatch. They start timing when they see the bricks clapped and stop when they hear the sound.
  4. Repeat this several times and get an average time.
  5. Use the formula (distance = speed x time ) to find the speed of sound.

  
• Measuring the Speed of Water Ripples

  1.Use a ripple tank

  2. Motor causes wooden bar to move up and down

  3. Produces waves in the form of ripples

  4. Light shines and creates shadow of waves on white card underneath

  A) water

  B) motor

  C) wooden bar

  D) shadows cast by ripples

  E) white card

  
• Measuring Frequency

  1.Start a stopwatch when first wave passes a fixed point

  2. Count number of waves that pass this point in a set time

  3. Divide set time by number of waves to find time period (T)

  4. Frequency (f) calculated using equation: f = 1/T

  A) frequency
• Measuring Wavelength


  1.Use a camera to capture an image of the waves

  2. Measure distance between two wavefronts with a metre ruler

  3. Count number of waves between wavefronts

  4. Divide total distance by number of waves to get wavelength (λ)

  
• Measuring Speed


  1.Determine mean values for frequency and wavelength

  2. Time how long it takes for one wavefront to travel the distance of the white card

  3. Measure length of card

  4. Speed (v) calculated by dividing distance by time:
• When measuring the speed of water ripple, don't measure the length of only 1 wave directly from the white card.

  For when taking a picture of it, the waves on the photograph are stationary

  • A more accurate measurement of length can be made against the metre rule.
  • Measuring the length across multiple wavelengths and using this to calculate a mean gives a more accurate value of one wavelength.
• Measuring Waves on a String:

  1. Set up your equipment, then switch on the signal generator and tweak the FREQUENCY of the signal generator to get a clear wave pattern on the string, which depends on the string's length and the weight attached.

  
• Measuring Waves on a String:

  2. After getting a clear wave pattern, measure the WAVELENGTH, using a metre ruler. It's most ACCURATE to measure multiple wavelengths at once. Then divide the total LENGTH by the NUMBER of wavelengths to find the FULL wavelength

  3. The FREQUENCY is the setting on the SIGNAL GENERATOR.

  4. Calculate the SPEED of the wave on the string using the formula

  
• How to investigate how the speed of a wave on a stretched string depends on the tension in the string:

  • Take away masses from the string
  • adjust frequency using the signal generator
  • observe a steady pattern to measure the wavelength
  • calculate wave speed from frequency and wavelength

  
• • The frequency of the signal generator is increased.
  • This makes the wavelength of the wave change.
  • The wave speed stays the same.

  Describe how the apparatus could be adjusted to show one complete wave without reducing the frequency.

  Add more masses to the string.

  
• The control variables in the method:

  • Tension in the string
  • length of string
  • type of string

  
• • The metre rule is too short
  • The string is raised up
  • The string moves

  
• • Measure the distance between the student with the bricks and the wall using a tape measure.
  • Measure the time taken from banging the bricks to the echo using the stopwatch.
  • double the distance to give the distance travelled.
  • Then use the equation: (Distance = speed x time) to find the speed of sound.
  • repeat timings and calculate a mean.

  
• place a floating object on the surface of the water, it will stay in the same place or only bop up & down if the water doesn't move