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Waves closes the first half of the syllabus and it rewards neat memory more than clever thinking. Organ pipes, beats and stationary waves — each one has a short formula and a standard question built around it. If the open pipe and the closed pipe ever get mixed up in your head, fix that today, because the paper has asked it again and again. Ten questions below. Give them ten honest minutes.
What this chapter carries in NEET(UG)
- Usually 2 to 3 questions every year, which is 8 to 12 marks.
- Organ pipes and beats are the regular visitors.
- Stationary waves and the speed of a wave on a string fill the rest.
What the syllabus says
In the syllabus (Unit 10, Oscillations and Waves): Wave motion, longitudinal and transverse waves, speed of a travelling wave, the displacement relation for a progressive wave, the principle of superposition, reflection of waves, standing waves in strings and organ pipes, the fundamental mode and harmonics, and beats.
Taken out in 2024: the Doppler effect in sound.
Taken from the NMC syllabus for NEET (UG) 2026, the latest one published. See the full syllabus, unit by unit.
Formulas you must know by heart
| Wave speed | v = fλ |
| Progressive wave | y = A sin(ωt − kx), k = 2π/λ |
| Speed on a stretched string | v = √(T/μ) |
| Speed of sound in a gas | v = √(γP/ρ) |
| Speed of sound and temperature | v ∝ √T |
| Stationary wave | node to node = λ/2 |
| Open pipe | fn = nv/2L, every harmonic present |
| Closed pipe | fn = (2n − 1)v/4L, odd harmonics only |
| Beat frequency | f = |f1 − f2| |
| Fundamental of a closed pipe | f₁ = v/4L, and a closed pipe of the same length sounds an octave lower than an open one |
Compare the two pipe lines carefully. A closed pipe of the same length sounds one octave lower than an open one, and it leaves out every even harmonic. That one comparison has carried more NEET(UG) questions than any other part of this chapter.
Ten questions. Give yourself ten minutes.
Write your answers down before you scroll. A question you looked up is a question you have not answered.
Q1. A wave of frequency 500 Hz has a wavelength of 0.6 m. Its speed is
- (a) 300 m/s
- (b) 500 m/s
- (c) 833 m/s
- (d) 0.0012 m/s
Q2. If the tension in a stretched string is made four times, the speed of a transverse wave on it becomes
- (a) double
- (b) half
- (c) four times
- (d) unchanged
Q3. In a stationary wave the distance between two consecutive nodes is
- (a) λ
- (b) λ/2
- (c) λ/4
- (d) 2λ
Q4. Two tuning forks of frequencies 256 Hz and 260 Hz are sounded together. The number of beats heard per second is
- (a) 2
- (b) 4
- (c) 8
- (d) 516
Q5. Sound waves cannot travel through
- (a) a solid
- (b) a liquid
- (c) a gas
- (d) a vacuum
Q6. The fundamental frequency of an organ pipe closed at one end and of length L is
- (a) v/2L
- (b) v/4L
- (c) v/L
- (d) 2v/L
Q7. A closed organ pipe produces
- (a) only even harmonics
- (b) only odd harmonics
- (c) all harmonics
- (d) no harmonics
Q8. A source of sound moves towards a stationary listener. The frequency heard by the listener
- (a) increases
- (b) decreases
- (c) stays the same
- (d) falls to zero
Q9. The speed of sound in air increases with a rise in
- (a) pressure
- (b) temperature
- (c) frequency
- (d) wavelength
Q10. Two waves y1 = a sinωt and y2 = a sin(ωt + π) travel together. The amplitude of the resultant is
- (a) 2a
- (b) a
- (c) zero
- (d) a√2
Answer key, with a hint for each
| Q1 | (a) | v = fλ = 500 × 0.6. |
| Q2 | (a) | v = √(T/μ), and √4 = 2. |
| Q3 | (b) | Nodes come every half wavelength. So do antinodes, and a node and the next antinode are λ/4 apart. |
| Q4 | (b) | The beat frequency is simply the difference, 260 − 256. |
| Q5 | (d) | Sound is a mechanical wave and needs a material to push on. Light does not. |
| Q6 | (b) | A closed pipe holds a quarter of a wavelength in its fundamental, so λ = 4L and f = v/4L. |
| Q7 | (b) | The closed end must be a node and the open end an antinode, and only odd multiples fit that pattern. |
| Q8 | (a) | The source keeps catching up with its own waves, so the wavefronts crowd together and the pitch rises. |
| Q9 | (b) | v ∝ √T in kelvin. Pressure alone makes no difference, because P and ρ change together. |
| Q10 | (c) | A phase difference of π means the two waves are exactly opposite at every instant, so they cancel. |
Now mark yourself honestly
NEET(UG) marks the way it marks. Use the same rule here:
- +4 for a right answer
- −1 for a wrong one
- 0 for a blank
So ten questions here are out of 40. In the real paper, 45 Physics questions are out of 180.
If you scored 32 or more, the basics of this chapter are secure. Move to harder questions, not more of these.
If you scored below 24, do not feel bad about it. You have just found out something useful before the exam did. Go back to the formula table above, learn it properly, and sit these ten again tomorrow.
And if you guessed a few and they landed, count those as wrong. A guess that works once will not work in May.
The full chapter, on a clock
Ten questions tell you a little. Forty-five tell you the truth.
The Beginner paper for Waves is waiting for you on the portal: 45 questions, 45 minutes, marked out of 180, with the answer key and a hint for every question. Sit it tonight and you will know exactly where this chapter stands.
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