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.3 Wave Phenomena — IB Physics SL Revision Notes & Topical Questions

5 min read 10 parts Lesson 13 of 31 1 quiz

📚 IB Physics SL 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.3 Wave Phenomena — IB PHYSICS SL notes: Describe reflection, refraction, diffraction and superposition of waves, apply Snell's law and the critical angle, and analyse double-slit interference.Wavefront — a line or surface joining points in phaseRay — a line perpendicular to the…

At a boundary
Law of reflection
Refractive index
What the symbols mean
Total internal reflection
Application

Part 1 of 8Wavefronts and rays

Wavefront

Wavefront a line or surface joining points in phase

Ray

Ray a line perpendicular to the wavefronts showing the direction of energy transfer

Use

Use wavefronts and rays describe waves in two and three dimensions

Part 2 of 8Reflection and transmission

At a boundary

At a boundary part of the wave is reflected and part is transmitted

Law of reflection

Law of reflection the angle of incidence equals the angle of reflection

Angles

Angles they are measured from the normal

Part 3 of 8Refraction

Cause

Cause a change of speed at a boundary changes the wavelength and, for oblique incidence, the direction

Refractive index

Refractive index n = c/v
What the symbols mean: n = refractive index (no unit) · c = speed of light in a vacuum (3.00 × 10⁸ m s⁻¹) · v = speed of light in the material (m s⁻¹)

Snell's law

Snell's law n₁ sin θ₁ = n₂ sin θ₂,
so n₁/n₂ = sin θ₂/sin θ₁ = v₂/v₁
What the symbols mean: n = refractive index (no unit) · i or θ₁ = angle of incidence · r or θ₂ = angle of refraction
- (both measured from the normal)

Direction

Direction light bends towards the normal on entering a medium where it travels more slowly

Frequency

Frequency it is unchanged

Part 4 of 8Critical angle and total internal reflection

Critical angle and total internal reflection

Critical angle

Critical angle for light going from higher to lower refractive index, the angle of refraction reaches 90° at the critical angle
sin θ_c = n₂/n₁.

Total internal reflection

Total internal reflection light in the denser medium meeting the boundary at more than the critical angle is not transmitted

Application

Application optical fibres

Part 5 of 8Diffraction

Diffraction

Diffraction the spreading of a wave through an aperture or round an obstacle

Size of gap

Size of gap it is greatest when the gap is comparable to the wavelength

What changes

What changes only the direction of the energy spread changes
Wavelength, frequency and speed are unchanged.

Spreading

Spreading a narrower slit or longer wavelength gives more spreading

Part 6 of 8Superposition and coherence

Superposition

Superposition the resultant displacement is the sum of the individual displacements

Coherent sources

Coherent sources a steady interference pattern needs a constant phase difference, so the same frequency

Part 7 of 8Path difference

1Constructive interference

Constructive interference sources in phase give maximum amplitude when path difference = nλ

2Destructive interference

Destructive interference sources in phase give minimum amplitude when path difference = (n + ½)λ

Feature	Constructive	Destructive
Path difference (sources in phase)	nλ	(n + ½)λ
Phase difference	0, 2π, 4π …	π, 3π …
Resultant amplitude	Maximum	Minimum
Light pattern	Bright fringe	Dark fringe

Part 8 of 8Young's double slit

Set-up

Set-up monochromatic light through two slits of separation d gives equally spaced bright and dark fringes on a screen at distance D

Fringe spacing

Fringe spacing s = λD/d, valid for D much greater than d

One source illuminates two narrow slits, making them coherent.

Each slit diffracts the light so the two beams overlap.

Where the path difference is a whole number of wavelengths, bright fringes form.

Where it is an odd number of half-wavelengths, dark fringes form.

Measure several fringe spacings and divide to reduce the uncertainty.

Key terms

Term	Meaning
Wavefront	A surface joining points on a wave that are in phase.
Ray	A line showing the direction of energy transfer, perpendicular to wavefronts.
Refractive index	The ratio of the speed of light in a vacuum to its speed in the medium.
Critical angle	The angle of incidence in the denser medium for which the angle of refraction is 90°.
Diffraction	The spreading of a wave as it passes through an aperture or round an obstacle.
Superposition	The addition of the displacements of two or more waves at a point.
Coherent sources	Sources with a constant phase difference.
Path difference	The difference in distance travelled by two waves from their sources to a point.

Avoid these mistakes

Saying refraction changes frequency — it changes speed and wavelength only.

Applying total internal reflection from the less dense to the denser medium.

Saying diffraction changes the wavelength of the wave.

Last updated: 13 October 2026