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Sound: SPI Physics

Sound has 9 questions in the SPI bank, eight EASY and one MODERATE, all from sample papers and mock tests. Five are about sound as a wave and how fast it travels in air, water and steel; the other four ask how we speak and hear and where reflected sound and ultrasound are used. None needs a long calculation: each is a fact or an order to remember, so learn the order solids, liquids, gases and the job of each part of the ear.

The handout has every subtopic, worked example, formula and trap with answers shown. The formula sheet is the chapter’s formulas and traps alone, on one page.

SPI home All formulas on one page

Subtopic notes

Formula & revision sheet

1 formulas · 3 reference tables · 12 gotchas across all subtopics — the exam-eve cheat-sheet

Sound Waves and Their Speed

Formulas (1)

Sound as a mechanical wave: v = fλ · Wave speed $v = f\lambda \qquad T = \frac{1}{f}$

Reference tables (1)

How fast sound travels, and what changes it5 rows

Medium	Speed of sound
Vacuum	Sound cannot travel
Air at 0 °C	about 331 m/s
Air at 20 °C	about 343 m/s
Water	about 1500 m/s, over four times the speed in air
Steel	about 5000 to 6000 m/s Fastest of the media the questions use.

Warmer air carries sound faster; colder air carries it slower.

Watch out for (7)

Thinking light needs a medium too
→ Sound as a mechanical wave: v = fλ
Calling sound transverse
→ Sound as a mechanical wave: v = fλ
Leaving kilohertz unconverted
→ Sound as a mechanical wave: v = fλ
Sound is fastest in air
→ How fast sound travels, and what changes it
The source sets the speed
→ How fast sound travels, and what changes it
Heat slows sound down
→ How fast sound travels, and what changes it
Sound is slower in water than in air
→ How fast sound travels, and what changes it

Hearing, Speech and Uses of Sound

Reference tables (2)

How we speak and how we hear6 rows

Part	Its job
Vocal cords (in the larynx)	Vibrate to make the voice
Pinna (outer ear)	Collects sound and sends it down the ear canal
Eardrum	A thin membrane that vibrates when sound reaches it
Hammer, anvil and stirrup (middle ear)	Amplify the vibrations and pass them to the inner ear The stirrup is the smallest bone in the body.
Cochlea (inner ear)	Turns vibrations into electrical signals
Auditory nerve	Carries the signals to the brain

Outer ear collects, middle ear amplifies, inner ear converts.

Uses of reflected sound and ultrasound7 rows

Use	How sound is used
Curved soundboard, curved ceiling	Reflect sound evenly to every part of a hall
Megaphone, horn	Reflections send the sound forward in one direction
Stethoscope	The heartbeat's sound is reflected along the tube to the ear
Echocardiography	Ultrasound echoes give an image of the heart Ultrasound, not X-rays.
Ultrasonography	Ultrasound images of organs and of a baby in the womb
SONAR	Ultrasound echoes find the depth of the sea and locate submarines
Bats	Find their way and their prey by ultrasound echoes

Reflected sound is used in halls; ultrasound echoes are used in hospitals and at sea.

Watch out for (5)

The middle ear bones raise the pitch
→ How we speak and how we hear
The eardrum makes the voice
→ How we speak and how we hear
A soundboard absorbs sound
→ Uses of reflected sound and ultrasound
Heart scans use X-rays
→ Uses of reflected sound and ultrasound
Expecting an echo from a near wall
→ Uses of reflected sound and ultrasound

Question weightage by concept

4 concepts · 9 questions — where the marks actually sit, so you know what to drill first

Sound Waves and Their Speed5 questions · 56%

Concept	Qs	Share
How fast sound travels, and what changes it	4	44%
Sound as a mechanical wave: v = fλ	1	11%

Hearing, Speech and Uses of Sound4 questions · 44%

Concept	Qs	Share
How we speak and how we hear	2	22%
Uses of reflected sound and ultrasound	2	22%

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