Measuring waves on a string | Exit Quiz | Oak National Academy

In an experiment, a variable that must be kept the same so it does not affect the results, is called a ___ variable.

Answer explanation

Control variables are the quantities that must be kept the same during experiments so they don’t affect the results.

Which images show a standing wave on a string?

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• 
• 
• 

Answer explanation

With a standing wave, the entire string oscillates in a stable pattern, and the wave does not appear to travel down the string.

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NGSS.HS-PS4-1

NGSS.HS-PS4-5

The length of string oscillating in this image is 90 cm. What is the wavelength of the waves?

• 30 cm

• 60 cm

• 90 cm

• 180 cm

Answer explanation

For this standing wave, one wavelength is 2 thirds of the string length. 2 thirds of 90 cm is 60 cm.

Tags

NGSS.HS-PS4-1

Starting with the measurement of the string length, put the steps in order to find the speed of waves on a string from a standing wave pattern.

• Slowly increase the frequency of the oscillator until a standing wave is seen.

• Record the frequency from the signal generator and work out the wavelength.

• Calculate the wave speed using speed = frequency x wavelength.

• Measure the length of the string using a metre rule.

Answer explanation

The length of the string is required to find the different wavelengths. The frequency can then be changed to give standing waves. The wavelength of each standing wave can be found. Using the frequency and wavelength, the wave speed can be calculated.

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NGSS.HS-PS4-1

Suggest which of the following could affect the speed of waves on a string?

• The frequency of the waves

• The wavelength of the waves

• The amplitude of the waves

• The tension of the string

• The density of the string

Answer explanation

Only properties of the medium affect the speed of the waves. Properties of the string include tension, density, mass and thickness.

Tags

NGSS.HS-PS4-1

Waves on a string have a frequency of 10 Hz and a wavelength of 20 cm. The frequency is increased from 10 Hz to 40 Hz. Nothing else changed. How would the wavelength be affected?

• The wavelength would reduce from 20 cm to 5 cm

• The wavelength would reduce from 20 cm to 10 cm

• The wavelength would stay the same

• The wavelength would increase from 20cm to 40 cm

• The wavelength would increase from 20 cm to 80 cm

Answer explanation

As the string is unchanged wave speed is the same; wavelength and frequency are inversely proportional. So wavelength changes by the inverse proportion. Frequency increased by a factor of 4, so wavelength must decrease to 1/4. 1/4 of 20 cm is 5 cm.

Tags

NGSS.HS-PS4-1