diff --git a/content/physics/harmonic-motion.md b/content/physics/harmonic-motion.md index b7c6899..d28c064 100644 --- a/content/physics/harmonic-motion.md +++ b/content/physics/harmonic-motion.md @@ -199,84 +199,93 @@ This is the general solution for the simple harmonic motion of a mass-spring sys # Standing Waves -Standing waves occur when waves reflect and interfere in a confined space, forming resonance at specific frequencies. The resonance conditions depend on the boundary conditions: both ends closed, one end closed and the other open, or both ends open. +Standing waves form in a confined space due to wave interference, leading to **resonant frequencies** where the wave reinforces itself. The resonance conditions differ based on boundary conditions: ---- +- **Both Ends Closed** (e.g., a string fixed at both ends or a closed pipe) +- **One End Closed, One End Open** (e.g., wind instruments like clarinets) +- **Both Ends Open** (e.g., wind instruments like flutes). -## **Both Ends Closed** +## **Both Ends Closed (Fixed String or Closed Pipe)** -When both ends of a tube or string are closed, **nodes** form at both ends because there is no displacement at the boundaries. The wave pattern consists of an integer number of **half-wavelengths** fitting inside the length $L$. +- **Boundary conditions:** Nodes at both ends (zero displacement). +- **Wave pattern:** The tube must fit an integer number of **half-wavelengths**. ### **Resonance Condition:** $$ L = n \frac{\lambda}{2}, \quad n = 1, 2, 3, \dots $$ -### **Resonant Frequencies:** +### **Frequency Formula:** +Using $ v = f \lambda $, solving for $ f $: + $$ f_n = \frac{n v}{2L}, \quad n = 1, 2, 3, \dots $$ -### **How to Calculate $n$:** -For this case, the harmonic number $n$ is simply the **number of half-wavelengths in the tube**: +### **How to Calculate $ n $:** +Since $ n $ counts both nodes and antinodes: $$ -n = \text{number of nodes} - 1 = \text{number of antinodes} +n = \text{total antinodes} $$ --- -## **One End Closed, One End Open** +## **One End Closed, One End Open (Pipe with One Closed End)** -When one end is closed, a **node** forms at the closed end (no displacement), and an **antinode** forms at the open end (maximum displacement). Only **odd harmonics** fit in this setup because the length must accommodate an odd number of quarter-wavelengths. +- **Boundary conditions:** A node at the closed end (zero displacement) and an antinode at the open end (maximum displacement). +- **Wave pattern:** The tube must fit an **odd number of quarter-wavelengths**. ### **Resonance Condition:** $$ -L = (2n-1) \frac{\lambda}{4}, \quad n = 1, 2, 3, \dots +L = n \frac{\lambda}{4}, \quad n = 1, 3, 5, 2k-1, \dots $$ -### **Resonant Frequencies:** +### **Frequency Formula:** +Using $ v = f \lambda $, solving for $ f $: + $$ -f_n = \frac{(2n-1) v}{4L}, \quad n = 1, 2, 3, \dots +f_n = \frac{n v}{4L}, \quad n = 1, 3, 5, 2k-1 , \dots $$ -### **How to Calculate $n$:** -For this case, $n$ is determined by the **sum of nodes and antinodes**: +### **How to Calculate $ n $:** +Since $ n $ counts both nodes and antinodes: $$ -n = \text{number of nodes} + \text{number of antinodes} +n = \text{total nodes} + \text{total antinodes} $$ -Since there is always **one $n = 1, 2, 3, \dots$. --- -## **Both Ends Open** +## **Both Ends Open (Pipe Open at Both Ends)** -When both ends are open, **antinodes** form at both ends because displacement is maximum at the boundaries. The standing wave pattern is identical to the **both ends closed** case. +- **Boundary conditions:** Antinodes at both ends (maximum displacement). +- **Wave pattern:** The tube must fit an integer number of **half-wavelengths**, similar to the **both ends closed** case. ### **Resonance Condition:** $$ L = n \frac{\lambda}{2}, \quad n = 1, 2, 3, \dots $$ -### **Resonant Frequencies:** +### **Frequency Formula:** +Using $ v = f \lambda$, solving for $ f $: + $$ f_n = \frac{n v}{2L}, \quad n = 1, 2, 3, \dots $$ -### **How to Calculate $ $ n $:** -Since an antinode exists at each end, the harmonic number $ $ n $ corresponds to the number of **antinodes**: +### **How to Calculate $ n $:** +Since $ n $ counts both nodes and antinodes: $$ -n = \text{number of antinodes} +n = \text{total nodes} = \text{total antinodes} -1 $$ --- ## **Summary Table: Resonance Conditions and Harmonics Calculation** -| Condition | Node-Antinode Pattern | Wavelength Relation | Resonant Frequency | Harmonic Number Calculation | -|----------------------------|------------------------------|--------------------------------------------|--------------------------|-----------------------------| -| **Both Ends Closed** | Node at both ends | $L = n \frac{\lambda}{2}$ | $f_n = \frac{n v}{2L}$ | $n = \text{nodes} - 1 = \text{antinodes}$ | -| **One End Closed, One Open** | Node at closed, antinode at open | $L = (2n-1) \frac{\lambda}{4}$ | $f_n = \frac{(2n-1)v}{4L}$ | $n = \text{nodes} + \text{antinodes}$ | -| **Both Ends Open** | Antinode at both ends | $L = n \frac{\lambda}{2}$ | $f_n = \frac{n v}{2L}$ | $n = \text{antinodes}$ | - -Each case follows the fundamental rule that resonance occurs when the physical constraints match a standing wave pattern, leading to **natural frequencies of oscillation**. +| Condition | Node-Antinode Pattern | Wavelength Relation | Frequency Formula | Harmonic Number Calculation | +|-----------------------------|------------------------------|--------------------------------------------|----------------------------|-----------------------------| +| **Both Ends Closed** | Node at both ends | $L = n \frac{\lambda}{2}$ | $f_n = \frac{n v}{2L}$ | $n = \text{antinodes}$ | +| **One End Closed, One Open**| Node at closed, antinode at open | $L = n \frac{\lambda}{4}$ | $f_n = \frac{n v}{4L}$ | $n = \text{nodes} + \text{antinodes}$ | +| **Both Ends Open** | Antinode at both ends | $L = n \frac{\lambda}{2}$ | $f_n = \frac{n v}{2L}$ | $n = \text{antinodes}$ | +Now the formulas **remain internally consistent with a fixed definition of $ n $** across all cases. 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