كيف يحسب الرقم الهيدروجيني pH للمحاليل؟ How to calculate pH and pOH?

يحسب الرقم الهيدروجيني بالعلاقة: pH = -log[H⁺]، وللمحاليل المائية عند 25°C: pH + pOH = 14. إذا كان pH 7 فالمحلول قاعدي. [الصيغة الرمزية الموزونة: pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴]

Theme C — Wave Behaviour

C.2.1 Properties of Waves — IB Physics HL Revision Notes & Topical Questions

5 min read 9 parts Lesson 12 of 37 1 quiz

📚 IB Physics HL Hub / Topical Revision

Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution

pH = -log[H⁺]  |  pOH = -log[OH⁻]  |  pH + pOH = 14  |  [H⁺][OH⁻] = 10⁻¹⁴

Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14

Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.

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Lesson summary

C.2.1 Properties of Waves — IB PHYSICS SL notes: Describe a wave using displacement, amplitude, wavelength, frequency, period and speed, and use v = fλ.Travelling wave — a repeating disturbance that transfers energy from one place to another without transferring matterWaves are g…

Particle motion
Mechanical waves
Electromagnetic waves
Displacement x (m)
Amplitude x0 (m)
Wavelength λ (m)

Section 1 of 9What a wave is

What a wave is

Travelling wave

Travelling wave a repeating disturbance that transfers energy from one place to another without transferring matter
Waves are generated by oscillating sources and travel away from them.

Particle motion

Particle motion each particle of the medium, or point of the field, oscillates about a fixed equilibrium position
A cork on a pond bobs up and down as ripples pass but does not travel with them.

Mechanical waves

Mechanical waves sound, water waves and waves on a string need a medium whose particles interact

Electromagnetic waves

Electromagnetic waves they need no medium and travel through a vacuum

Section 2 of 9Quantities describing a wave

Displacement x (m)

Displacement x (m) the distance of a point from its equilibrium position, which can be positive or negative

Amplitude x0 (m)

Amplitude x0 (m) the maximum magnitude of displacement from equilibrium
It relates to the energy carried.

Wavelength λ (m)

Wavelength λ (m) the shortest distance between two points that are in phase, such as crest to crest

Period T (s)

Period T (s) the time for one complete oscillation to pass a fixed point

Frequency f (Hz)

Frequency f (Hz) the number of complete oscillations passing a fixed point per second

Wave speed v (m s⁻¹)

Wave speed v (m s⁻¹) the distance travelled by the pattern, and hence the energy, per unit time

Section 3 of 9Wave equation

Period and frequency

Period and frequency f = 1/T
What the symbols mean: T = period, the time for one complete wave (s) · f = frequency (Hz)
The source sets the frequency, and it does not change when the wave enters a new medium.

Derivation

Derivation in one period the pattern advances one wavelength, so v = λ/T, which gives v = fλ

For light

For light in a vacuum v is replaced by c, so c = fλ

Constant speed

Constant speed a higher frequency means a shorter wavelength, and a longer wavelength means a lower frequency

Section 4 of 9Reading wave graphs

1Displacement–distance graph

Displacement–distance graph a snapshot at one instant that shows the wave shape along the direction of travel
The spacing between neighbouring peaks is the wavelength.
The maximum height is the amplitude.

2Displacement–time graph

Displacement–time graph it follows one point as time passes
The spacing between neighbouring peaks is the period.
The maximum height is still the amplitude.

3Marking arrows

Marking arrows draw them from the top of one peak to the top of the next, and measure amplitude from equilibrium

4Units

Units convert cm to m and ms to s before substituting

Section 5 of 9Phase

1In phase

In phase points a whole number of wavelengths apart move together

2Antiphase

Antiphase points an odd number of half-wavelengths apart always move in opposite directions

3Phase difference

Phase difference for two points a distance d apart it is 2πd/λ radians, or 360°d/λ

Section 6 of 9Wavefronts and intensity

Wavefront

Wavefront a line or surface joining points of the same phase
The ray is the direction of travel and is perpendicular to the wavefront.

Intensity

Intensity the energy per second passing through unit area at right angles to the wave, in W m⁻²

Amplitude link

Amplitude link intensity is proportional to the square of the amplitude, I ∝ x₀²
Doubling the amplitude quadruples the intensity.

Point source

Point source the energy spreads over a sphere, so I ∝ 1/r²

Sinusoidal form

Sinusoidal form a travelling sinusoidal wave shows as a sine curve in both kinds of graph

Section 7 of 9More from the specification

1Transverse vs Longitudinal Waves

Waves are classified by particle vibration direction: in transverse waves vibrations are perpendicular to the direction waves propagate,
while in longitudinal waves oscillations are parallel.

2Wave Equation

The wave equation relates wave speed v (in m/s), frequency f (in Hz),
and wavelength lambda as v = f * lambda, applicable across all mechanical and electromagnetic waves.
- (defined in metres)

3Electromagnetic Spectrum

Electromagnetic waves propagate through vacuum at 3.0 * 10⁸ m/s, spanning a continuous spectrum of wavelengths from gamma rays to radio waves.

4Audible Sound Wave Range

Sounds propagate as mechanical longitudinal compression waves through matter, with normal human hearing spanning an audible frequency range of 20 Hz to 20 kHz.

5Spectrum

Range of colours in white light.

6Longitudinal wave

Wave whose vibrations are parallel to the direction of travel

7Transverse wave

Wave whose vibration is at right angles to the direction of propagation

8Electromagnetic spectrum

Continuous family of waves from radio waves to gamma rays

Section 8 of 9Key terms

Term	Meaning
Amplitude	Maximum magnitude of displacement from equilibrium.
Wavelength	Shortest distance between two points in phase.
Period	Time for one complete oscillation, T = 1/f.
Frequency	Number of oscillations per second, in hertz.
Wavefront	A line or surface of points that are in phase.
Intensity	Power per unit area received perpendicular to the wave direction.
Phase difference	Fraction of a cycle by which two points are out of step.

Section 9 of 9Exam technique

Reading wavelength from a displacement–time graph — the horizontal spacing there is the period.

Thinking the particles of the medium travel along with the wave — they only oscillate about equilibrium.

Quoting amplitude as peak-to-peak height — it is measured from equilibrium to a peak.

Saying frequency changes when a wave enters a new medium — the source fixes the frequency.

Forgetting that intensity depends on amplitude squared, not amplitude.

Last updated: 18 October 2026