11th Class Physics Chapter 8 Notes | Get Now
11th Class Physics Chapter 8 Notes are your go-to resource for mastering the Waves chapter in FSc Part 1. This chapter covers some of the most frequently tested concepts in Punjab Board exams, including types of waves, stationary waves, sound, beats, and the Doppler effect. These notes break everything down in a simple, easy-to-understand way.
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11th Class Physics Chapter 8 Notes — Chapter Overview
Chapter 8 is titled Waves and is part of the FSc Part 1 Physics syllabus under the Punjab Board. It builds on the basic concepts of oscillations from Chapter 7 and extends them into wave motion, sound, and real-world applications.
Major topics covered in the 11th Class Physics Chapter 8 Notes:
- Difference and similarities between longitudinal and transverse waves
- Waveforms on a Cathode Ray Oscilloscope (CRO)
- Stationary waves and conditions for their formation
- Wave terminology: crest, trough, node, anti-node
- Speed of sound in different media
- Beats and their role in tuning musical instruments
- The Doppler effect and its applications
- Galaxy motion and red shift
Short Questions & Answers — 11th Class Physics Chapter 8 Notes
Here is a complete summary of all 11 short questions from this chapter:
Q 8.1 — Common Features of Longitudinal and Transverse Waves
Both types of waves share the following features:
- Both are mechanical waves
- Both transfer energy from one point to another without transferring matter
- Both produce disturbance in the medium through which they travel
- The relation v = fλ holds for both, where v is speed, f is frequency, and λ is wavelength
Q 8.2 — Waveforms on CRO
From the five waveforms (A to E) shown on a cathode ray oscilloscope:
- Loudest note: Trace B, because loudness depends on amplitude of vibration — Trace B has the greatest amplitude
- Highest frequency: Trace B, because it has the maximum number of waves per second
Q 8.3 — Can Two Identical Waves Produce a Stationary Wave?
No. Two identical waves travelling in the same direction cannot produce a stationary wave. To form a stationary wave, two identical waves must travel in opposite directions.
Q 8.4 — Wave with Zero Displacement at Some Points
A wave where some particles permanently show zero displacement is a stationary wave. The points of zero displacement are called nodes.
Q 8.5 — Crest, Trough, Node, and Anti-node
- Crest: Upper portion of a transverse wave from the mean position
- Trough: Lower portion of a transverse wave from the mean position
- Node: Point where displacement of the stationary wave is permanently zero
- Anti-node: Point where displacement of the stationary wave is maximum
Q 8.6 — Why Does Sound Travel Faster in Solids Than in Gases?
The speed of sound is given by: v = √(E/ρ)
Speed is directly proportional to the square root of modulus of elasticity. Solids have much greater elasticity than gases, and although their density is also higher, the effect of elasticity is stronger. So sound travels faster in solids than in gases.
Q 8.7 — How Are Beats Useful in Tuning Musical Instruments?
A standard instrument is sounded together with the instrument to be tuned. The beats per second are recorded. The frequency of the instrument being tuned is adjusted until it produces zero beats with the standard. This way, musical instruments are tuned to a precise frequency using the phenomenon of beats.
Q 8.8 — Frequency of Beats Formula
When two notes of frequency f₁ and f₂ are sounded together and f₁ > f₂:
The number of beats per second = f₁ − f₂
So the correct answer is (iii) f₁ − f₂.
Q 8.9 — Explosion: Ground Tremor Before Sound
Sound travels faster through solid ground than through air. So seismic waves from a distant explosion reach an observer through solid earth much faster than the sound waves travelling through air. This creates the observed time difference.
Q 8.10 — Why Sound Travels Faster in Warm Air Than Cold Air
The speed of sound in air is: v = √(γP/ρ)
Speed is inversely proportional to √ρ. Warm air has lower density than cold air, so sound travels faster in warm air than in cold air.
Q 8.11 — How Should a Sound Source Move So Frequency Does Not Change?
If both the sound source and the observer move in the same direction with the same velocity, their relative velocity is zero. Therefore, the frequency of the sound does not change — this is a key principle of the Doppler effect.
Solved Problems — 11th Class Physics Chapter 8 Notes
The 11th Class Physics Chapter 8 Notes include 10 fully solved numerical problems. Here is a clear summary of each:
Problem 8.1 — Radio Transmitter Wavelength and Wave Speed
Given: Wavelength = 1500 m at 200 KHz; find wavelength at 1000 KHz
Answers:
- Speed of radio waves = 3 × 10⁸ m/s
- Wavelength for 1000 KHz transmitter = 300 m
Problem 8.2 — Speed of Sound from Two Speakers
Given: Two speakers 3 m apart, frequency 344 Hz, microphone 4 m away
Solution: Using path difference and v = fλ
Answer: Speed of sound = 344 m/s
Problem 8.3 — Stationary Wave: Wavelength and Fundamental Frequency
Given: String 120 cm long, vibrating in 4 segments at 120 Hz
Answers:
- Wavelength = 0.6 m
- Fundamental frequency = 30 Hz
Problem 8.4 — Effect of Length and Tension on Frequency
Given: String frequency = 300 Hz
(a) When length reduced by one-third → Frequency = 450 Hz
(b) When tension increased by one-third → Frequency = 346 Hz
Problem 8.5 — Organ Pipe: Open and Closed Ends
Given: Organ pipe length = 50 cm, speed of sound = 350 m/s
(a) Open at both ends:
- Fundamental frequency = 350 Hz
- Next harmonic = 700 Hz
(b) Closed at one end:
- Fundamental frequency = 175 Hz
- Next harmonic = 525 Hz
Problem 8.6 — Church Organ Frequency Range
Given: Pipe lengths from 30 mm to 4 m, speed of sound = 340 m/s
Answers:
- Frequency for minimum length = 2833 Hz
- Frequency for maximum length = 21.2 Hz
Problem 8.7 — Frequency of Second Tuning Fork
Given: Beat frequency = 3 Hz, one fork = 256 Hz; after loading beat = 1 Hz
Answer: Frequency of second tuning fork = 253 Hz
Problem 8.8 — Doppler Effect: Two Cars on Motorway
Given: Car P at 12 m/s, Car Q at 20 m/s, apparent frequency = 830 Hz
Answer: Frequency heard by Q’s own driver = 810 Hz
Problem 8.9 — Train Horn: Speed and Distance
Given: Train horn at 1200 Hz; observer hears 1140 Hz after departure; speed of sound = 340 m/s
Answers:
- Speed of train = 17.89 m/s
- Distance covered in 50 s = 448 m
Problem 8.10 — Galaxy Moving Away from Earth
Given: Calcium α line at 478 nm (observed) vs 397 nm (lab); speed of light = 3 × 10⁸ m/s
Answers:
- The galaxy is moving away from Earth (apparent frequency < fundamental frequency)
- Speed of galaxy = 6.12 × 10⁷ m/s
Key Formulas at a Glance
| Formula | Description |
|---|---|
| v = fλ | Wave speed equation |
| Beats = f₁ − f₂ | Beat frequency |
| v = √(E/ρ) | Speed of sound in medium |
| fₐ = (v/v−uₛ) × f | Doppler effect (source approaching) |
| fₐ = (v/v+uₛ) × f | Doppler effect (source receding) |
| f₁ = v/2l | Fundamental frequency (open pipe) |
| f₁ = v/4l | Fundamental frequency (closed pipe) |
Why These Notes Are Perfect for FSc Exam Prep
The 11th Class Physics Chapter 8 Notes are specially designed for students following the Punjab Board curriculum. All short questions match the pattern of past board exams, and each numerical problem is solved step-by-step so you can follow every calculation.
Students who study these FSc Part 1 Waves notes consistently score better in both objective and subjective parts of the paper. You can also check our [internal link] 11th Class Physics important questions 2026 guide and [internal link] FSc Part 1 past papers for extra practice.
Suggested Image Alt Text: 11th Class Physics Chapter 8 Notes Waves Short Questions and Solved Problems FSc Part 1
FAQs
Q1. What topics are covered in 11th Class Physics Chapter 8 Notes?
The 11th Class Physics Chapter 8 Notes cover the Waves chapter, including longitudinal and transverse waves, stationary waves, crest, trough, nodes, anti-nodes, beats, speed of sound in different media, the Doppler effect, and 10 fully solved numerical problems as per the Punjab Board syllabus.
Q2. How many short questions are in Chapter 8 of FSc Part 1 Physics?
There are 11 short questions in Chapter 8 of FSc Part 1 Physics. They cover important concepts like wave terminology, conditions for stationary waves, beat frequency, and why sound travels faster in warm air and solid mediums compared to air or cold conditions.
Q3. What is the formula for the frequency of beats in Chapter 8?
The frequency of beats is equal to the difference in frequencies of two notes sounded together. If two notes have frequencies f₁ and f₂ where f₁ > f₂, then beats per second = f₁ − f₂. This is a key formula tested in board exams and covered in detail in Chapter 8 notes.
Q4. What is the Doppler effect explained in FSc Part 1 Physics Chapter 8?
The Doppler effect is the change in observed frequency when a source of sound and an observer are in relative motion. If the source moves toward the observer, frequency increases. If it moves away, frequency decreases. This concept is applied in Problems 8.8, 8.9, and 8.10 of the chapter.
Q5. Why does sound travel faster in solids than in gases?
Sound travels faster in solids because the speed of sound depends on the modulus of elasticity. Solids have a much higher elasticity compared to gases. Even though solids are denser, the effect of higher elasticity is greater, which results in a faster speed of sound in solids than in gases.
Q6. How many solved problems are in 11th Class Physics Chapter 8?
There are 10 fully solved numerical problems in Chapter 8. These cover topics including radio wave speed, speed of sound using two speakers, stationary waves, organ pipe harmonics, tuning fork beats, the Doppler effect, and the speed of a galaxy moving away from Earth using wavelength shift.