Year 10 Physics: Sound Waves and Ultrasound Explained

🔊 What Are Sound Waves?

Sound waves are a type of mechanical wave that travel through air, liquids, or solids by vibrating particles. They are longitudinal waves, meaning the particles vibrate back and forth in the same direction that the wave moves. These vibrations cause changes in air pressure, which our ears detect as sound.

📐 Properties of Sound Waves

• Frequency: This is how many waves pass a point each second, measured in hertz (Hz). Higher frequency means a higher pitch.
• Wavelength: The distance between one compression and the next in the wave.
• Amplitude: Relates to the loudness; bigger amplitude means a louder sound.
• Speed: Sound travels at different speeds depending on the medium — it travels faster in solids, slower in liquids, and slowest in gases like air because the particles are closer together in solids.

🎵 Behaviour of Sound Waves

Sound waves can reflect (bounce off surfaces), refract (change direction when entering a different medium), diffract (bend around obstacles), and be absorbed. These behaviours explain why you can hear someone around a corner or why sound is louder in certain rooms.

🔍 What is Ultrasound?

Ultrasound refers to sound waves with frequencies higher than 20,000 Hz, which is above the range of human hearing. We cannot hear ultrasound because our ears are not sensitive to such high frequencies.

⚙️ How Ultrasound Works

Ultrasound uses high-frequency sound waves that travel through the body and reflect off tissues and organs. The reflected waves are detected and translated into images. This is possible because different tissues reflect sound differently, providing detailed pictures inside the body without using harmful radiation.

🩺 Uses of Ultrasound

• Medical imaging: Ultrasound is widely used for scanning unborn babies (prenatal scans) and examining organs like the liver or kidneys.
• Industrial testing: Checking for cracks in metal or finding flaws in structures without damaging them.
• Cleaning: Uses ultrasound waves to clean delicate objects like jewellery and lenses.
• Navigation and communication: Animals like bats and dolphins use ultrasound for echolocation.

📊 Differences Between Ordinary Sound Waves and Ultrasound

❓ 10 Examination-Style 1-Mark Questions with 1-Word Answers on Sound Waves and Ultrasound

1. What type of wave is a sound wave?
   Answer: Longitudinal
2. What device uses ultrasound to create images inside the body?
   Answer: Scanner
3. What property of sound waves determines their pitch?
   Answer: Frequency
4. Which part of the ear detects sound vibrations?
   Answer: Cochlea
5. What is the unit used to measure the frequency of sound waves?
   Answer: Hertz
6. What happens to the speed of sound in warmer air?
   Answer: Increases
7. Ultrasound waves have a frequency higher than the upper limit of _________.
   Answer: Hearing
8. What term describes the bending of sound waves around obstacles?
   Answer: Diffraction
9. What is the name of the process where ultrasound waves reflect off different tissues?
   Answer: Echo
10. Which substance do sound waves travel fastest through: air, water, or solid?
    Answer: Solid

❓ 10 Examination-Style 2-Mark Questions with 1-Sentence Answers on Sound Waves and Ultrasound

1. What type of wave is a sound wave?
   A sound wave is a longitudinal mechanical wave that requires a medium to travel through.
2. How does the frequency of a sound wave affect its pitch?
   A higher frequency results in a higher pitch, while a lower frequency produces a lower pitch.
3. Why can sound waves not travel through a vacuum?
   Sound waves need particles in a medium to vibrate and transfer the energy, so they cannot travel through a vacuum where there are no particles.
4. What property of a sound wave determines its loudness?
   The amplitude of a sound wave determines its loudness, with larger amplitudes producing louder sounds.
5. Explain how ultrasound waves are different from normal sound waves.
   Ultrasound waves have frequencies higher than 20,000 hertz, which is above the human hearing range.
6. Name one use of ultrasound in medicine.
   Ultrasound is used in medical imaging, such as scanning a baby in the womb.
7. How do ultrasound waves help in detecting flaws inside metal objects?
   Ultrasound waves reflect off boundaries inside the metal, allowing detection of internal cracks or flaws.
8. What happens to the speed of sound when it travels from air to water?
   The speed of sound increases when it travels from air to water because water particles are closer together.
9. Why is ultrasound preferred over normal sound waves for medical imaging?
   Ultrasound can produce clearer images of internal body parts because it has a higher frequency and better resolution.
10. What causes an echo to occur?
    An echo occurs when sound waves reflect off a surface and travel back to the listener.

❓ 10 Examination-Style 4-Mark Questions with 6-Sentence Answers on Sound Waves and Ultrasound

Question 1:

Explain how the frequency of a sound wave affects the pitch that we hear.

Answer:
The frequency of a sound wave is the number of vibrations or waves that pass a point each second. A higher frequency means the waves vibrate faster. When the frequency increases, the pitch of the sound becomes higher. For example, a whistle has a high-frequency sound. Conversely, lower frequency sound waves produce a lower pitch, such as a drum beat. Our ears detect these differences and send signals to the brain to interpret pitch.

Question 2:

Describe how sound waves travel through different states of matter and which state they travel fastest in.

Answer:
Sound waves are mechanical waves that need a medium to travel through, such as solids, liquids, or gases. They travel by vibrating the particles in these materials. Sound waves travel fastest in solids because particles are closely packed and can pass vibrations quickly. In liquids, the particles are further apart, so sound travels slower than in solids. In gases, the particles are most spread out, making sound travel slowest. Therefore, sound moves fastest in solids, slower in liquids, and slowest in gases.

Question 3:

What is ultrasound and how is it different from audible sound waves?

Answer:
Ultrasound refers to sound waves with a frequency higher than what humans can hear, typically above 20,000 hertz. Audible sound waves have frequencies between about 20 hertz and 20,000 hertz, which humans can detect. Unlike audible sounds, ultrasound waves are used in medical imaging because they can reflect off tissues inside the body. These waves can provide detailed images without using harmful radiation. Ultrasound properties make it useful for scanning babies in the womb. So, ultrasound differs from audible sound mainly in frequency and its practical applications.

Question 4:

Explain how ultrasound can be used in medical imaging.

Answer:
Ultrasound medical imaging works by sending high-frequency sound waves into the body using a probe. These sound waves travel through tissues and reflect back when they hit different structures like organs or bones. The reflected ultrasound waves are detected and create an image on a screen. These images help doctors examine internal organs or monitor a developing baby. Ultrasound is safe because it does not use radiation like X-rays. This makes it useful for routine check-ups and diagnosing health problems.

Question 5:

What causes sound waves to be louder or quieter?

Answer:
The loudness of sound depends on the amplitude of the sound waves. Larger amplitude means the waves carry more energy and sound louder to our ears. If the amplitude is small, the sound will be quieter. For example, shouting produces sound waves with a bigger amplitude than whispering. Loudness is measured in decibels, with higher values indicating louder sounds. Our ears sense loud sounds by detecting stronger vibrations.

Question 6:

How does the ear detect sound waves?

Answer:
Sound waves enter the ear through the outer ear canal and cause the eardrum to vibrate. These vibrations are passed through tiny bones in the middle ear called ossicles. The ossicles amplify the vibrations and transfer them to the cochlea in the inner ear. The cochlea contains hair cells that move in response to vibrations, converting them into electrical signals. These signals travel along the auditory nerve to the brain. The brain then interprets them as sound.

Question 7:

What is the difference between longitudinal and transverse waves, and which type are sound waves?

Answer:
Longitudinal waves have vibrations that move parallel to the direction of wave travel. Transverse waves have vibrations perpendicular to the wave direction. Sound waves are longitudinal because the air particles vibrate back and forth in the same direction as the wave moves. This means areas of compression and rarefaction occur in sound waves. Light waves are an example of transverse waves. Understanding wave types helps explain how sound propagates through air.

Question 8:

Why can’t sound travel through a vacuum?

Answer:
Sound waves require particles to vibrate and carry the energy of the wave. A vacuum has no particles because it is an empty space with no matter. Without particles to vibrate, sound cannot be transmitted. This is why in space, where there is a near vacuum, sound cannot travel. Astronauts rely on radios, which use electromagnetic waves, to communicate instead. So, the absence of a medium stops sound waves from existing.

Question 9:

How does the Doppler effect change the sound of a moving vehicle?

Answer:
The Doppler effect happens when a sound source moves towards or away from an observer. If the vehicle moves closer, the sound waves get compressed, increasing frequency and pitch. This makes the sound seem higher-pitched as it approaches. When the vehicle moves away, the waves stretch out, lowering frequency and pitch. This causes the sound to drop as the vehicle drives past. It explains the change in siren sound of an ambulance.

Question 10:

What safety precautions should be taken when using ultrasound machines in medical settings?

Answer:
Ultrasound machines should be used by trained professionals to ensure correct operation. The machine must be calibrated regularly to avoid excessive energy output. Exposure time should be kept as short as possible to prevent any tissue heating. Protective gel used during scanning helps transmit sound waves effectively and prevents air gaps. Patients should inform professionals if they feel discomfort during scanning. Following these precautions keeps ultrasound safe and effective.

❓ 10 Examination-Style 6-Mark Questions with 10-Sentence Answers on Sound Waves and Ultrasound

Question 1:

Explain how sound waves travel through different mediums and why their speed varies.

Answer:
Sound waves are vibrations that travel through a medium by causing particles to vibrate. They need a medium like air, water, or solids to move; sound cannot travel through a vacuum because there are no particles to transmit the vibrations. In solids, particles are closely packed, so vibrations pass quickly from one particle to another, making sound travel fastest in solids. In liquids, particles are less tightly packed than in solids, so sound moves slower than in solids but faster than in gases. In gases like air, particles are far apart, so sound travels the slowest. Temperature also affects the speed; warmer air makes particles vibrate faster, which increases sound speed. For example, sound travels at about 343 m/s in air at room temperature but about 1500 m/s in water. The differences in particle spacing and elasticity of the medium cause these speed variations. This explains why sound can travel through walls (solid) faster than through air. Understanding this helps in applications like medical ultrasound and sonar.

Question 2:

Describe how ultrasound is produced and detected in medical imaging.

Answer:
Ultrasound is a type of sound wave with a frequency higher than 20,000 Hz, which humans cannot hear. It is produced using a transducer that converts electrical energy into sound waves by vibrating at high frequencies. When these ultrasound waves enter the body, they travel through tissues and reflect off boundaries between different types of tissues or organs. The transducer then detects the waves that bounce back or echo from these boundaries. The time taken for echoes to return helps calculate the distance of the tissue or organ from the transducer. A computer processes these echoes to create an image of the inside of the body. This method is safe because ultrasound waves do not use ionising radiation, unlike X-rays. The images help doctors see organs, monitor babies during pregnancy, and detect abnormalities. Ultrasound can also measure blood flow by detecting changes in frequency when waves bounce off moving blood cells. This technology relies on the properties of sound waves and their interactions with tissues.

Question 3:

Explain why animals like bats and dolphins use ultrasound and how their echo-location works.

Answer:
Bats and dolphins use ultrasound for echo-location to navigate and find food in their environment. They emit high-frequency sound waves that are above the human hearing range, which allows for very detailed echoes. When these ultrasound waves hit an object, they reflect back to the animal. The animal’s brain calculates the distance and size of the object based on how long it takes for the echoes to return and the change in frequency. This process helps bats avoid obstacles and locate insects they hunt at night. Dolphins use similar echoes underwater to find fish and swim safely. Ultrasound waves travel well in water, allowing dolphins to detect objects far away. Echo-location provides animals with a ‘sound map’ of their surroundings, which is crucial in dark or murky conditions. The high frequency of ultrasound gives better resolution, so the animals can detect small objects. This natural use of ultrasound is mimicked in human technologies like sonar.

Question 4:

Discuss the advantages and disadvantages of using ultrasound in medical diagnosis.

Answer:
One advantage of ultrasound scanning is that it is non-invasive and painless, making it comfortable for patients. It does not use harmful ionising radiation like X-rays, so it is safer for repeated use, especially for monitoring pregnancies. Ultrasound images show real-time movement, useful for watching a baby’s heartbeat or blood flow in vessels. It is relatively cheap compared to other imaging methods like MRI or CT scans. Portable ultrasound machines also allow scans in various settings, such as ambulances. However, a disadvantage is that ultrasound does not penetrate bone well, limiting its use for imaging structures inside or behind bones, like the brain. It is also less detailed than some other scans for certain tissues. The quality of images can depend on the skill of the person performing the scan. Ultrasound images can sometimes be hard to interpret without training. Overall, ultrasound is a valuable tool with some limitations.

Question 5:

Describe how the wavelength and frequency of a sound wave are related to the pitch and explain how changing one affects the other.

Answer:
Pitch is how high or low a sound seems to our ears and depends on the frequency of the sound wave. Frequency is the number of wave vibrations per second and is measured in hertz (Hz). Higher frequency waves have higher pitches, like a whistle, while lower frequency waves have lower pitches, like a drum. Wavelength is the distance between one point on a wave and the next identical point, such as from one peak to the next. The wavelength and frequency are inversely related because the speed of sound in a medium is constant at a given temperature. This means if the frequency increases, the wavelength must decrease, and vice versa. A shorter wavelength corresponds to a higher frequency and higher pitch. For example, tuning a guitar string tighter increases the frequency, making the pitch higher and the wavelength shorter. Understanding this helps us control and identify sounds in music and technology.

Question 6:

Explain what a longitudinal wave is and how sound waves are an example of this kind of wave.

Answer:
A longitudinal wave is a wave where the particle vibrations are parallel to the direction the wave travels. This means that particles vibrate back and forth along the same line as the wave moves. Sound waves are longitudinal waves because when we produce sound, air particles vibrate in the same direction as the sound travels. The vibrations create areas where particles are close together called compressions, and areas where particles are spread apart called rarefactions. These compressions and rarefactions travel through the medium, transferring energy from one place to another. For example, when you talk, your vocal cords make the air vibrate in longitudinal waves that reach the listener’s ear. In this way, sound waves carry energy through air or other materials. This is different from transverse waves, such as light waves, where particle vibration is perpendicular to the wave direction. Recognising sound as a longitudinal wave helps us understand how it moves and interacts with objects.

Question 7:

Explain why ultrasound waves have higher frequencies than audible sound waves and how this affects their use in imaging.

Answer:
Ultrasound waves have frequencies higher than 20,000 Hz, which means they vibrate faster than sound waves we can hear. The high frequency means the waves have shorter wavelengths. Shorter wavelengths allow ultrasound to resolve smaller details because they can reflect from tiny structures inside tissues. This high-frequency nature makes ultrasound very useful for medical imaging, as it can produce clearer and more detailed images than lower-frequency sounds. However, because ultrasound waves have such high frequency, they are absorbed more quickly and cannot travel very far, which limits their use to imaging relatively shallow parts of the body. Lower-frequency sound waves can travel further but produce lower-resolution images. The ability of ultrasound to provide high-resolution images without the risks of X-rays makes it ideal for scanning soft tissues. Thus, the high frequency of ultrasound is key to its role in safe, detailed medical diagnosis.

Question 8:

Describe how sound wave amplitude affects the loudness of a sound and give an example.

Answer:
The amplitude of a sound wave is the height of the wave and relates to the energy or intensity of the wave. Larger amplitudes mean the particles in the medium vibrate more intensely, producing louder sounds. Conversely, smaller amplitudes mean quieter sounds. For example, when you speak loudly, your vocal cords vibrate with greater amplitude, producing sound waves with bigger compressions and rarefactions in the air. These waves cause bigger pressure changes that your ear detects as loud sounds. When whispering, the amplitude is much smaller, so the sound is quiet. The frequency of the sound affects pitch, but amplitude mainly affects loudness. Thus, controlling amplitude allows us to change how loud a sound is without changing its pitch. Understanding amplitude helps in designing musical instruments and sound equipment to produce desired sound levels.

Question 9:

Explain why sound cannot travel through a vacuum and what this means for space exploration.

Answer:
Sound cannot travel through a vacuum because sound waves need a medium like air, water, or solids for particles to vibrate and pass the wave on. In a vacuum, there are no particles to carry these vibrations, so sound waves cannot move. This means in space, which is mostly a vacuum, no sound can be heard because there is no air or other material for sound waves to travel through. For space exploration, this means astronauts cannot rely on sound to communicate outside their spacecraft. Instead, they use radios, which send signals as electromagnetic waves that do not require a medium and can travel through the vacuum of space. This difference between sound and radio waves is crucial for designing communication systems for space missions. Knowing this helps us understand the challenges of space travel and how we overcome them.

Question 10:

Describe what happens when an ultrasound wave hits a boundary between two different tissues in the body.

Answer:
When an ultrasound wave hits a boundary between two tissues with different densities, some of the wave is reflected back while some continues through the second tissue. This happens because the change in tissue density causes a difference in acoustic impedance. The greater the difference in impedance, the bigger the reflection. The ultrasound transducer detects the reflected waves, or echoes, which return at different times depending on the depth of the boundary. The machine calculates the distance to the boundary using the speed of ultrasound in the tissue and the time taken for the echo to return. Multiple reflections from different boundaries create a pattern of echoes that a computer uses to form an image of the internal structures. This image helps doctors see organs, muscles, and fluids. If the tissues have similar densities, less ultrasound is reflected, making the boundary harder to detect. Understanding this process is essential in how ultrasound imaging produces detailed pictures inside the body.