GCSE Physics revision

Waves for detection and exploration (physics only) (HT only)

Waves in air, fluids and solids

AQA 4.6.1.5

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AQA student objectives

Learning pathway

All · Most · Some

ALL 🎯

Explain how differences in wave speed, absorption and reflection in solids and liquids are used to detect and investigate hidden structures.

MOST 🎯🎯

Apply the scientific explanation of waves for detection and exploration to a relevant example.

SOME 🎯🎯🎯

Analyse a new situation involving waves for detection and exploration and explain the scientific reasoning.

Revision summary

Key knowledge

Read on screen, then print for Cornell-style active revision.

Using Waves to Detect Faults in Materials

Waves can be used to detect cracks or faults in solid materials, such as concrete, by sending a sound wave through the material and analysing the reflected signals.
When a wave hits a boundary or fault, some of the wave is reflected back and some is transmitted, producing multiple peaks on a signal screen.
A single peak on the screen indicates no fault, whilst two or more peaks indicate the presence of a crack or boundary within the material.

1. Using Waves to Detect Faults in MaterialsAQA

Notes

Waves can be used to detect cracks or faults in solid materials, such as concrete, by sending a sound wave through the material and analysing the reflected signals.
When a wave hits a boundary or fault, some of the wave is reflected back and some is transmitted, producing multiple peaks on a signal screen.
A single peak on the screen indicates no fault, whilst two or more peaks indicate the presence of a crack or boundary within the material.

Calculating Distance Using Wave Reflection

The distance to a fault or boundary can be calculated using the equation: d = v × t, where d is distance, v is speed, and t is time.
Because the wave travels to the boundary and back, the calculated distance must be divided by 2 to find the actual depth or distance to the fault.
For example, if sound travels at 330 m/s and takes 0.5 seconds to return, the distance is 330 × 0.5 / 2 = 82.5 m.
This method can be applied to measuring depths such as ocean floors, soil layers, or concrete foundations.

2. Calculating Distance Using Wave ReflectionAQA

Notes

The distance to a fault or boundary can be calculated using the equation: d = v × t, where d is distance, v is speed, and t is time.
Because the wave travels to the boundary and back, the calculated distance must be divided by 2 to find the actual depth or distance to the fault.
For example, if sound travels at 330 m/s and takes 0.5 seconds to return, the distance is 330 × 0.5 / 2 = 82.5 m.
This method can be applied to measuring depths such as ocean floors, soil layers, or concrete foundations.

Ultrasound and Infrasound Definitions

Ultrasound refers to any sound wave with a frequency above the upper limit of human hearing, which is above 20,000 Hz (20 kHz).
Infrasound refers to any sound wave with a frequency below the lower limit of human hearing, which is below 20 Hz.
Humans can only hear sounds within the frequency range of 20 Hz to 20,000 Hz.

3. Ultrasound and Infrasound DefinitionsAQA

Notes

Ultrasound refers to any sound wave with a frequency above the upper limit of human hearing, which is above 20,000 Hz (20 kHz).
Infrasound refers to any sound wave with a frequency below the lower limit of human hearing, which is below 20 Hz.
Humans can only hear sounds within the frequency range of 20 Hz to 20,000 Hz.

Medical Uses of Ultrasound

Ultrasound is used in medical imaging to scan internal organs such as the heart and kidneys without invasive procedures.
Ultrasound scans are commonly used to image unborn babies, as the sound waves reflect off each boundary (skin, womb, baby) producing distinct peaks on a screen.
A computer processes the reflected signals and their timings to build up a detailed image of internal structures.

4. Medical Uses of UltrasoundAQA

Notes

Ultrasound is used in medical imaging to scan internal organs such as the heart and kidneys without invasive procedures.
Ultrasound scans are commonly used to image unborn babies, as the sound waves reflect off each boundary (skin, womb, baby) producing distinct peaks on a screen.
A computer processes the reflected signals and their timings to build up a detailed image of internal structures.

Seismic Waves and Earthquakes

Seismic waves are waves produced by earthquakes, and they radiate outward from the epicentre, which is the point on the Earth's surface directly above where the earthquake originates.
There are two main types of seismic waves: P waves (primary waves) and S waves (secondary waves).
By detecting seismic waves at different locations around the Earth, scientists can determine the internal structure of the Earth.

5. Seismic Waves and EarthquakesAQA

Notes

Seismic waves are waves produced by earthquakes, and they radiate outward from the epicentre, which is the point on the Earth's surface directly above where the earthquake originates.
There are two main types of seismic waves: P waves (primary waves) and S waves (secondary waves).
By detecting seismic waves at different locations around the Earth, scientists can determine the internal structure of the Earth.

P Waves (Primary Waves)

P waves are longitudinal waves, meaning the particles vibrate in the same direction as the wave travels.
P waves are faster than S waves and can travel through solids, liquids, and gases.
P waves can travel through all layers of the Earth, including the liquid outer core and the solid inner core, though they are refracted (bent) as they pass through different layers.

6. P Waves (Primary Waves)AQA

Notes

P waves are longitudinal waves, meaning the particles vibrate in the same direction as the wave travels.
P waves are faster than S waves and can travel through solids, liquids, and gases.
P waves can travel through all layers of the Earth, including the liquid outer core and the solid inner core, though they are refracted (bent) as they pass through different layers.

S Waves (Secondary Waves)

S waves are transverse waves that are slower than P waves and can only travel through solid materials.
S waves cannot travel through liquids or gases, so they are blocked by the liquid outer core of the Earth.
Because S waves do not reach the far side of the Earth (the shadow zone), this provides evidence that the outer core is liquid.

7. S Waves (Secondary Waves)AQA

Notes

S waves are transverse waves that are slower than P waves and can only travel through solid materials.
S waves cannot travel through liquids or gases, so they are blocked by the liquid outer core of the Earth.
Because S waves do not reach the far side of the Earth (the shadow zone), this provides evidence that the outer core is liquid.

The Shadow Zone

The shadow zone is the region on the opposite side of the Earth from an earthquake's epicentre where S waves cannot be detected.
Only P waves are detected in the shadow zone, which confirms that the outer core is liquid since S waves cannot pass through it.
Weak P waves are detected in the shadow zone due to refraction, which provides evidence that the inner core is solid.

8. The Shadow ZoneAQA

Notes

The shadow zone is the region on the opposite side of the Earth from an earthquake's epicentre where S waves cannot be detected.
Only P waves are detected in the shadow zone, which confirms that the outer core is liquid since S waves cannot pass through it.
Weak P waves are detected in the shadow zone due to refraction, which provides evidence that the inner core is solid.

Structure of the Earth Revealed by Seismic Waves

The Earth has four main layers: the crust, the mantle, the liquid outer core, and the solid inner core.
The crust is approximately 50–60 km thick, and scientists know this because the speed of seismic waves changes at this depth.
The outer core is known to be liquid because S waves cannot pass through it, whilst the inner core is known to be solid because P waves are refracted through it.
The refraction of seismic waves as they pass through different layers allows scientists to determine the density and thickness of each layer.

9. Structure of the Earth Revealed by Seismic WavesAQA

Notes

The Earth has four main layers: the crust, the mantle, the liquid outer core, and the solid inner core.
The crust is approximately 50–60 km thick, and scientists know this because the speed of seismic waves changes at this depth.
The outer core is known to be liquid because S waves cannot pass through it, whilst the inner core is known to be solid because P waves are refracted through it.
The refraction of seismic waves as they pass through different layers allows scientists to determine the density and thickness of each layer.

Key Summary: Waves for Exploration

Both ultrasound and seismic waves use the principle of wave reflection and refraction to explore structures that cannot be seen directly.
The equation d = v × t (remembering to divide by 2 for reflected waves) is essential for calculating distances in both industrial and geological contexts.
The behaviour of S and P waves provides the key evidence for our understanding of the Earth's internal structure.

10. Key Summary: Waves for ExplorationAQA

Notes

Both ultrasound and seismic waves use the principle of wave reflection and refraction to explore structures that cannot be seen directly.
The equation d = v × t (remembering to divide by 2 for reflected waves) is essential for calculating distances in both industrial and geological contexts.
The behaviour of S and P waves provides the key evidence for our understanding of the Earth's internal structure.