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.3.2 Reflection, Refraction and Transmission — IB Physics HL Revision Notes & Topical Questions

5 min read 11 parts Lesson 18 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.3.2 Reflection, Refraction and Transmission — IB PHYSICS SL notes: State and apply the law of reflection and Snell's law, and describe reflection, refraction, transmission and total internal reflection at a boundary.Possible outcomes — a wave meeting a boundary can be reflected…

Unchanged quantities
Smooth surface
Rough surface
Plane mirror
Unchanged quantity
Into a slower (optically denser) medium

Part 1 of 8What happens at a boundary

Possible outcomes

Possible outcomes a wave meeting a boundary can be reflected, refracted, transmitted or absorbed
The proportions depend on the media, the angle of incidence and the wave type.
A glass window lets light through and also gives a faint reflection of the room.

Medium

Medium in optics a transparent material is called a medium, and several are called media

Normal

Normal angles are measured between the ray and the normal, the line at 90° to the boundary at the point of incidence

All waves

All waves reflection, refraction and transmission occur for both transverse and longitudinal waves

Part 2 of 8Reflection

Reflection

Reflection a wave meets a boundary, does not pass through and bounces back into the original medium

Law of reflection

Law of reflection the angle of incidence equals the angle of reflection, θ_i = θ_r
The incident ray, reflected ray and normal lie in the same plane.

Unchanged quantities

Unchanged quantities frequency, wavelength and speed do not change on reflection

Smooth surface

Smooth surface specular reflection keeps parallel rays parallel and gives a clear image

Rough surface

Rough surface diffuse reflection occurs because each small facet obeys the law but faces a different direction

Plane mirror

Plane mirror the image is virtual, the same size as the object and as far behind the mirror as the object is in front

Part 3 of 8Refraction

Refraction

Refraction the change in direction of a wave when it crosses a boundary between media where its speed differs
Different parts of the wavefront change speed at different times as they hit the boundary.

Unchanged quantity

Unchanged quantity frequency stays the same, so the colour of light does not change

Changed quantities

Changed quantities speed and wavelength change

Into a slower (optically denser) medium

Into a slower (optically denser) medium the wave slows, its wavelength shortens and the ray bends towards the normal

Into a faster medium

Into a faster medium the wave speeds up, its wavelength lengthens and the ray bends away from the normal

Normal incidence

Normal incidence a ray along the normal passes straight through because the whole wavefront enters at once

Two boundaries

Two boundaries the refracted ray at the first boundary is the incident ray at the second, so label the diagram clearly

Part 4 of 8Snell's law and refractive index

Refractive index

Refractive index n = c/v,
so n ≥ 1 and it has no unit
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)
c is the speed of light in a vacuum and v the speed in the medium.

Snell's law

Snell's law n₁ sin θ₁ = n₂ sin θ₂
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)
Equivalent forms are sin θ₁/sin θ₂ = v₁/v₂ = λ₁/λ₂ = n₂/n₁.

Typical values

Typical values air 1.00, water 1.33, glass about 1.5 and diamond 2.42

Graph

Graph sin θ₁ against sin θ₂ for light entering glass from air is a straight line through the origin with gradient n of the glass

Apparent depth

Apparent depth for near-normal viewing, apparent depth = real depth × n₂/n₁, so an underwater object looks shallower

Part 5 of 8Refraction of water waves

Deep to shallow

Deep to shallow the waves slow down and the wavelength decreases, so peaks are closer together

Direction

Direction at an angle they bend towards the normal, so the angle of refraction is less than the angle of incidence

Part 6 of 8Transmission

Transmission

Transmission a wave passes through a substance and appears on the opposite side of a boundary
It is the opposite of reflection and refraction is one type of it.

Absorption

Absorption a transmitted wave has lower amplitude if some absorption has occurred

Distinction

Distinction with refraction there is always transmission and a change of direction, while with reflection there is no transmission into another medium

Part 7 of 8Total internal reflection

1Critical angle

Critical angle going from a higher to a lower index, the refracted angle reaches 90° at θ_c
sin θ_c = n₂/n₁, where n₁ > n₂.

2Total internal reflection

Total internal reflection if the incidence angle exceeds θ_c, all the light is reflected

3Two conditions

Two conditions light travels towards the lower-index medium and the angle of incidence exceeds the critical angle

4Applications

Applications optical fibres, binocular prisms and the sparkle of diamond
Diamond's high index gives a small critical angle of about 24°.

Part 8 of 8More from the specification

Key terms

Term	Meaning
Normal	Line perpendicular to the boundary at the point of incidence.
Refractive index	n = c/v, ratio of the speed of light in vacuum to that in the medium.
Snell's law	n₁ sin θ₁ = n₂ sin θ₂.
Critical angle	Angle of incidence in the denser medium giving a 90° refracted angle.
Total internal reflection	Complete reflection at a boundary when the incidence angle exceeds the critical angle.
Specular reflection	Reflection from a smooth surface giving a clear image.

Avoid these mistakes

Measuring angles from the surface rather than the normal.

Saying frequency changes on refraction — only speed and wavelength change.

Applying total internal reflection when going into a denser medium — it needs the lower-index medium beyond.

Using n = v/c instead of c/v.

Forgetting that some light is partly reflected at a boundary even when it refracts.

Last updated: 15 October 2026