Frequency
Contents
Key Stage 3
Meaning
Frequency is the number of waves that pass by in one second.
About Frequency
| Water Waves |
 |
| The frequency of this wave can be found by counting the number of times the red marker oscillates every second. |
- The higher the frequency the quicker the wave oscillates.
- In sound frequency is known as pitch. A high pitch is a high frequency.
- In light frequency affects the colour of the light. Red is a low frequency and violet is a high frequency.
Equation
Frequency = 1/(Period)
\(f = \frac{1}{T}\)
Where:
f = Frequency
T = time period (the time it takes for one wave to pass a point).
Key Stage 4
Meaning
Frequency is the number of waves that pass a given point in one second.
About Frequency
- Frequency is a scalar quantity because it has magnitude but no direction.
- The SI Unit of frequency is Hertz (Hz).
| Water Waves |
|
| The frequency of this wave can be found by counting the number of times the red marker oscillates every second. |
- The higher the frequency the quicker the wave oscillates.
- In sound frequency is known as pitch. A high pitch is a high frequency.
- In light frequency affects the colour of the light. Red is a low frequency and violet is a high frequency.
- When wave enters a new medium it will remain the same frequency but the wave speed and wavelength will change.
- Frequency can be found by counting the number of waves which pass a point in a given time and dividing this by the time.
Equation
Equation 1
NB: You do not need to remember this equation but you should know how to find frequency given the time taken for one wave to pass a point.
Frequency = 1/(Period)
\(f = \frac{1}{T}\)
Where: f = Frequency
T = time period (the time it takes for a wave to pass a point).
Equation 2
NB: You do not need to remember this equation but you should know how to find frequency given the number of waves passing a point and the time taken.
Frequency = (Number of Waves which pass a point)/(Time taken for waves to pass a point)
\(f = \frac{n}{t}\)
Where: f = Frequency
n = Number of waves which pass a point.
t = The time taken for those waves to pass a point.
Equation 3
NB: You should remember this equation with v as the subject of the formula.
Frequency = (Wave Speed)/(Wavelength)
\( f = \frac{v}{\lambda}\)
Where
\( \lambda\) = The wavelength of the wave.
\(v\) = The wave speed of the wave.
\(f\) = The frequency of the wave.
Example Calculations
Finding Frequency from Time Period
| Calculate the frequency of a wave with a period of 0.04 seconds. | A giant pendulum takes 16 seconds to make one complete oscillation. Calculate the frequency of the pendulum. |
| 1. State the known quantities
T = 0.04s |
1. State the known quantities
T = 16s |
| 2. Substitute the numbers into the equation and solve.
\( f = \frac{1}{T}\) \( f = \frac{1}{0.04}\) \( f = 25Hz\) |
2. Substitute the numbers into the equation and solve.
\( f = \frac{1}{T}\) \( f = \frac{1}{16}\) \( f = 0.0625Hz\) |
Finding Frequency from the number of waves and time taken
| A scientist wants to determine the frequency of a pendulum. They count that the pendulum oscillates 15 times over 20 seconds. Calculate the frequency of the pendulum. | A sailor notices a buoy bounce up and down 24 times over a minute. Calculate the frequency of the waves. |
| 1. State the known quantities
n = 15 t = 20s |
1. State the known quantities
n = 24 t = 60 |
| 2. Substitute the numbers into the equation and solve.
\(f = \frac{n}{t}\) \(f = \frac{15}{20}\) \(f = 0.75Hz\) |
2. Substitute the numbers into the equation and solve.
\(f = \frac{n}{t}\) \(f = \frac{24}{60}\) \(f = 0.4Hz\) |
Finding Frequency from Wavelength and Wave Speed
| A microwave travelling at a speed of 3.0x108m/s has a wavelength of 0.051m. Calculate the frequency of the wave correct to two significant figures. | An ultrasound wave of wavelength 0.125m passes through an Iron block at a speed of 5000m/s. Calculate the frequency of the wave correct to two significant figures. |
| 1. State the known quantities
v = 3.0x108m/s λ = 0.051m |
1. State the known quantities
v = 5000m/s λ = 0.125m |
| 2. Substitute the numbers into the equation and solve.
\( f = \frac{v}{\lambda}\) \( f = \frac{3.0 \times 10^8}{0.051}\) \( f = 5882352941Hz\) \( f \approx 5900000000Hz\) |
2. Substitute the numbers into the equation and solve.
\( f = \frac{v}{\lambda}\) \( f = \frac{5000}{0.125}\) \( f = 40000Hz\) |
References
AQA
- Frequency (f), pages 50-1, 583, GCSE Physics, Hodder, AQA
- Frequency, page 73, GCSE Physics; The Revision Guide, CGP, AQA
- Frequency, pages 189, 190, GCSE Combined Science Trilogy; Physics, CGP, AQA
- Frequency, pages 190-3, 200-1, 206-9, 213-15, 218, 222, 224, 236-7, 275, GCSE Physics; Student Book, Collins, AQA
- Frequency, pages 226, 227, GCSE Physics; The Complete 9-1 Course for AQA, CGP, AQA
- Frequency, pages 257, GCSE Combined Science Trilogy 2, Hodder, AQA
- Frequency; human hearing range, page 280, GCSE Physics; The Complete 9-1 Course for AQA, CGP, AQA
- Frequency; human hearing range, page 88, GCSE Physics; The Revision Guide, CGP, AQA
- Frequency; Measurement of, pages 260, GCSE Combined Science Trilogy 2, Hodder, AQA
- Frequency; of EM waves, pages 200, 203, GCSE Combined Science Trilogy; Physics, CGP, AQA
- Frequency; of EM waves, pages 242, 245, GCSE Physics; The Complete 9-1 Course for AQA, CGP, AQA
- Frequency; of EM waves, pages 76, 81, GCSE Physics; The Revision Guide, CGP, AQA
- Frequency; of mains electricity, page 66, GCSE Physics; Student Book, Collins, AQA
- Frequency; of mains supply, page 31, GCSE Physics; The Revision Guide, CGP, AQA
- Frequency; of mains supply, page 86, GCSE Combined Science Trilogy; Physics, CGP, AQA
- Frequency; of mains supply, page 89, GCSE Physics; The Complete 9-1 Course for AQA, CGP, AQA
- Frequency; table, pages 40-1, GCSE Physics; Student Book, Collins, AQA
Edexcel
- Frequency (waves), page 91, GCSE Physics, CGP, Edexcel
- Frequency (waves); of hearing, page 104, GCSE Physics, CGP, Edexcel
- Frequency (waves); of infrasound, page 109, GCSE Physics, CGP, Edexcel
- Frequency (waves); of ultrasound, page 106, GCSE Physics, CGP, Edexcel
- Frequency, pages 164-166, 168, GCSE Combined Science; The Revision Guide, CGP, Edexcel
- Frequency, pages 32-34, 43, GCSE Physics; The Revision Guide, CGP, Edexcel
- Frequency, pages 331, 340, GCSE Combined Science, Pearson Edexcel
- Frequency, pages 49, 72, GCSE Physics, Pearson Edexcel