Chapter 13 Wave Motion
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Wave 波是什麽
波（Wave）是指能夠在不傳遞物質的情況下，傳播能量或訊息的一種物理現象。 它是透過介質（如空氣、水、電磁場等）中的振動或擾動而傳播的。 波可以在各種媒介中傳播，包括機械波（如聲波和水波）和電磁波（如光波和無線電波）等。
Transverse Wave 橫波
oscillation perpendicular to the direction of travel, e.g. waves on a string
質點的振盪方向垂直於 波的傳播方向，例如以繩子產生的波
Longitudinal Wave 縱波
oscillation along the line of travel, e.g. sound wave
質點的振盪方向平行於波的傳播方向，例如聲波
Mechanical Wave 機械波
needs medium to travel, e.g. water waves
需要介質作傳遞，例如水波
Electromagnetic Wave 機械波
oscillation of electric and magnetic fields, e.g. light、
由振動的電場及磁場組成，例如光
Travelling wave 行波
the waveform propagates
波形向外傳播
Stationary Waves 駐波
the waveform does not propagate
波形停留在固定位置
Description of waves 波的描述
amplitude 振幅 A
maximum magnitude of displacement of an oscillating particle from its equilibrium position
從平衡位置起，質點振盪的最大位移量值
wavelength 波長 λ
minimum distance a wave repeats itself
在一個波中，重複波形的最小距離
frequency 頻率 f
number of waves produced in 1 s; unit: Hz
每秒可產生的波的數目。單位為赫茲 (Hz)
period 週期 T
time to produce one complete wave
產生一個完整的波所需的時間
frequency 頻率 f vs period 週期 T
$$T=\frac{1}{f}$$
Wave speed 波速率 v
distance travelled by a wave per unit time
波在每單位時間的傳播距離
$$v=\frac\lambda T=f\lambda $$
for transverse waves on a spring, the wave speed increases when the tension becomes larger or another lighter spring is used.
繩子的張力增加，或使用一條較輕的繩，皆會令繩子上的波速率提高。
**注意：增加f不會增加v，因爲當f增加，λ會減少，最後導致v依舊相同。
真正主宰v的是wave的tension以及wave的density
$$v=\sqrt{\frac{T}{\mu}}$$
例如：
將一條string拉緊會增加wave speed
將傳遞wave媒介的density下降，即mass下降，wave speed也會上升
Motion of particles 質點的運動
one complete oscillation for a particle in one period
質點在一個週期的時間完成一次振盪
如果把這据説得白話一點，就是當一個particle完成一次震蕩，整個wave就會向前邁進一個wavelength
two particles in phase 同相質點
- same motion
運動完全相同 - separation: λ, 2λ, 3λ…
相距：λ、2λ、3λ⋯⋯
two particles in antiphase 反相質點
- opposite motion
運動完全相反 - separation: ½λ, 1½λ, 2½λ…
相距：½λ、1½λ、2½λ⋯⋯
Transverse Wave vs Longitudinal Wave
橫波 vs 縱波
| Transverse Wave | Longitudinal Wave | |
| at rest | crest and trough | the middle particle between compression and rarefaction |
| highest speed | equilibrium position | compression and rarefaction |
Displacement–distance (s–d) graph 位移—距離關係線圖
- describe all particles on the wave
描述所有質點（就好像幫一個wave影相） - x-intercept x 軸截點：
- equilibrium position
平衡位置 - (for longitudinal waves) centre of compression/rarefaction
密部／疏部中心（ 縱波 ）
- equilibrium position
- can be deduced: A and λ
能夠從線圖求得：A 及 λ
Displacement–time (s–t) graph 位移—時間關係線圖
- describe one particle on the wave
描述一顆質點 - x-intercept: equilibrium position
x 軸截點：平衡位置 - can be deduced: A, f and T
能夠從線圖求得：A、f 和 T
Energy and matter 能量與物質
Waves transfer energy but not matter.
波傳遞能量但不傳遞物質。
Amplitude, frequency and wave speed
波幅，頻率與波速率
A wave with a larger amplitude has more energy but does not travel faster. Note that the wave speed depends on the medium.
波幅較大的波具有較高能量，但不代表速率較高。注意波的速率跟介質有關。
Chapter 14 Reflection Refraction and Diffraction
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Wavefronts 波陣面
- separated by one wavelength
相鄰波陣面相距一個波長 - particles on the wavefronts are in phase
波陣面上的質點皆同相
Rays 波陣面
- perpendicular to the wavefront
與波陣面互相垂直 - showing the direction of travel of the wave
顯示波的傳播方向
Reflection 反射
laws of reflection 反射定律：
- The incident ray, reϐlected ray and normal lie on the same plane.
入射線、反射線和法線都在同一平面上。 - The angle of reϐlection r is equal to the angle of incidence i.
反射角 r 等於入射角 i。
Refraction 折射
waves show refraction when its speed changes upon crossing a boundary
當波從一個介質進入另一個介質時，其速率會改變，這現象稱為折射
| Wave Speed ↓ | Wave Speed ↑ | |
| Frequency | remains unchanged | remains unchanged |
| Wavelength | ↓ | ↑ |
| Direction of Travel | towards the normal | away from the normal |
angle of incidence θ1 and angle of refraction θ2 入射角 θ1 和折射角θ2：
$$\frac{v_1}{v_2}=\frac{\lambda_1}{\lambda_2}=\frac{\sin\theta_1}{\sin\theta_2}$$
Diffraction 繞射
waves show diffraction when 波在下列情況出現繞射：
- passing the edge of an obstacle
經過障礙物的邊緣 - passing through a slit
通過縫隙 - passing around an obstacle
經過細小的障礙物
- passing the edge of an obstacle
- unique property of waves
波獨有的特性
因此，若果您要證明一樣東西是wave的話，其中一個方法就是證明那樣東西有diffraction
Degree of diffraction 繞射程度
Chapter 15 Interference and Stationary Waves
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Interference 干涉是什麽
Interference 干涉是指兩個或多個波在同一空間中相遇並產生相互作用的現象。 當波傳播到相遇點時，它們會相互疊加或相互幹擾，導致波的振幅、相位或能量變化。
干涉可以分為構造干涉和破壞干涉兩種類型。 構造干涉發生在兩個或多個波的峰值或谷值相遇時，波的振幅相加，導致波的幅度增加。 相反，破壞干涉發生在波的峰值和谷值相遇時，波的振幅相互抵消，導致波的幅度減小或完全消失。
Superposition 疊加
principle of superposition 疊加原理
when two waves meet, the resultant displacement is the vector sum of the two
當兩個波相遇時，質點的位移是原來兩個波的合量
**注意：當兩個waves相撞後，兩個waves會變回原來的樣子，即是 “掂行掂過”
Interference 干涉 深入探討
requires coherent sources
兩列波必須是相干的
for two coherent sources vibrating in phase 對於兩列相干而且同相的波
| Interference | Constructive | Destructive |
| Happens on | Antinodal Lines | Nodal Lines |
| Path Difference | 0, λ, 2λ … | ½λ, 1½λ, 2½λ … |
seperation between antinodal lines increases when 在下列情況，腹線與腹線間的距離會上升：
- the wavelength increases
波長增加 - the distance between two sources decreases
波源之間的距離減少
Coherent sources 相干波源
Two coherent sources have a constant phase difference. Their waves produced may not have the same amplitude.
兩個相干波源間的相變是固定的，但兩者的振幅不必相同。
Transverse stationary wave 橫向駐波
- superposition of incident wave and reflected wave
入射波和反射波疊加的結果 - particles’ oscillations: various amplitudes but same frequency
質點的振動：振幅各有不同但是頻率相同 - particles at nodes: always at rest (e.g. a)
處於波節的質點：在任何時間都是靜止的（ 例如質點 a ） - particles at antinodes: have the greatest amplitude (e.g. c)
處於 波腹的質點：振幅是最大的（ 例如質點 c ） - particles between two successive nodes are in phase
在兩個波節間，所有質點的振盪都是同相的 - particles on the two sides of a node are in antiphase
在一個波節兩端，質點的振盪是反相的 - wavelength = 2×distance between two successive nodes
波長 = 2×兩個相鄰波節的距離
Travelling vs Stationary
| Travelling waves | Stationary waves | |
| Frequency | same for all particles | same for all particles |
| Amplitude | same for all particles | different for particles between two nodes |
| Wavelength | distance between two successive particles in phase | 2× distance between two successive nodes |
| Phase | different for all particles within one wavelength | all particles between two successive nodes are in phase |
Constructive interference 相長干涉
At positions where constructive interference occurs, the displacement of the particle is not always the maximum.
在出現相長干涉的地方，質點的位移不是長期處於最大值。
Chapter 16 Light and Sound
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最後更加會講3大常見錯處！
Light 光是什麽
光（Light）是指電磁輻射的一種形式，它是由電磁波組成的。 光是一種能在真空和其他透明媒介中傳播的電磁輻射，其頻率範圍通常在可見光的範圍內，即從紅外線到紫外線。
Visible spectrum 可見光譜是什麽
from red to violet, f ↑ and λ ↓
光譜按 波長從長到短、頻率從低至高排列，依次為紅、橙、黃、綠、藍、靛、紫
Diffraction: single slit 光的單縫繞射
- diffraction: wave nature of light
繞射為光的波動本質 - slit must be very narrow
單縫必須非常狹窄，才能產生明顯的光繞射 - degree of diffraction ↑ 繞射程度 ↑：
- wavelength ↑ (violet to red)
波長 ↑（ 紫光到紅光 ） - slit width
狹縫闊度 ↓
- wavelength ↑ (violet to red)
Interference: double slit 光的雙縫干涉
- interference: wave nature of light
干涉為光的波動本質 - bright and dark fringes at the central part
中央部分出現亮紋及暗紋 - fringe separation 亮紋間距：
$$\Delta y=\frac{\lambda D}a$$
- D = screen–slit distance,
- a = slit separation
Interference: double slit 光的雙縫干涉 常見錯誤
The fringe separation ∆y is for a small portion at the central part of the interference pattern. When applying the formula, D ≫ ∆y and D ≫ a
亮紋間距 ∆y 的公式只對干涉圖案中間的一小部分有效。運用該方程的條件另外還有 D ≫ ∆y 和 D ≫ a。
Interference: plane transmission grating
光的干涉 ：平面透射光柵
multiple-slit interference
多縫干涉
$$d\sin\theta=m\lambda $$
- d = slit separation 縫距
- m = order of bright fringe 亮紋的級數
Electromagnetic waves (EM waves) 電磁波
oscillating electric field and magnetic field, perpendicular to each other
由振盪的電場和磁場組成，兩者的振盪方向互相垂直
transverse waves
本質為橫波
energy increases with frequency
頻率越高，能量越高
travel at speed of 3×108 ms-1 in a vacuum
在真空中的速率為 3×108 ms-1
Electromagnetic spectrum 電磁光譜
| Type of Radiation | Wavelength Range | Source | Detector | Application |
| Waves | 10⁻¹ to 10⁴ m | Radio & TV transmitter | antenna | Radio & TV broadcast |
| Microwaves | 10⁻³ to 10⁻¹ m | Microwave transmitter | crystal | Data transmission |
| Infrared | 10⁻⁶ to 10⁻³ m | Any object (lamp, spark) | phototransistor | Thermography, remote control |
| Visible Light | 4×10⁻⁷ to 7×10⁻⁷ m | Very hot object, lamp | our eye | Lighting |
| Ultraviolet | 10⁻⁹ to 10⁻⁸ m | X-ray tube, radioactive substance | fluorescent material | Water sterilization |
| X-rays | 10⁻¹⁰ m | X-ray tube | film | bone check |
| Gamma rays | 10⁻¹² m | Radioactive substance | Geiger–Müller tube | Tumor killing |
Sound wave 聲波
- longitudinal waves
縱波 - mechanical waves; requires a medium to travel
機械波，需要介質傳播 - speed is independent of frequency or amplitude; highest in solids, lowest in gases
在固體內速率最高，在氣體內則最低，跟其頻率及振幅無關
Audible sound and ultrasound 聽頻範圍及超聲波
- audible frequency range 聽頻範圍：
- f = 20 Hz 至 20 000 Hz
- f = 20 to 20 000 Hz
- 超聲波：f > 20 000 Hz
ultrasound: f > 20 000 Hz - applications of ultrasound 超聲波的應用：
- sonar, inspecting foetus, therapy, detecting ϐlaws, cleaning objects
- 聲納、檢查胎兒、超聲波掃描、檢查裂紋、超聲波清潔
Musical note 樂音
- regular waveform
波形具有一定規律 - frequency ↑, then pitch ↑
頻率增加，則音調增加 - amplitude ↑, then loudness ↑
振幅增加，則響度增加 - quality 音品:
- relating to waveform
跟波形有關 - different instruments produce sounds of different qualities
不同樂器產生的聲波的音品各有不同
- relating to waveform
Noise 噪音
- irregular waveform
波形沒有規律 - control measures 控制噪音的措施：
- building soundproof barriers
建造隔音屏障 - using low-noise materials for roads
路面鋪上低噪物料 - separating roads and houses with buffers
道路和住宅間增設緩衝區（ 例如樹木或多層停車場 ）
- building soundproof barriers
- protection measures 保護措施:
- avoid long exposure to noise
避免長時間處於高噪音環境 - wearing protective headphones
佩載耳筒
- avoid long exposure to noise
Sound intensity level 聲強級 L
increases with the energy carried by a sound wave
聲波的能量越高，聲強級越高
unit: dB
typical sound intensity levels 典型的聲強級：
| Sound | L/dB | Remarks |
| Threshold of hearing | 0 | Can be barely heard |
| Country park | 30 | |
| Conversation in quiet room | 60 | |
| Rail noise, 25 m away | 80 | Hearing damage after long exposure |
| Noisy disco | 100 | |
| Ship’s engine room | 120 | Painful to ears, permanent hearing loss |
| Jet engine, 50 m away | 140 | |
| Space shuttle engine | 200 | Immediate permanent hearing loss |
Comparison of light and sound 光波和聲波的比較
| Property | Light | Sound |
| Wave Type | Electromagnetic Wave | Mechanical Wave |
| Wave Motion | Transverse Wave | Longitudinal Wave |
| Speed in Air | ≈ 3×108 m/s | ≈ 3×102 m/s |
常見錯誤：Speed of EM waves 電磁波的速率
All EM waves have the same speed in a vacuum but they may have different speeds in other medium.
所有電磁波在真空中的速率相同，但在其他介質中則不盡相同。
常見錯誤：Vibrating string and sound wave
振動的弦跟聲波
The wave have the same frequency as that of the vibration of the
string. But it does not have the same wavelength or speed as the wave produced in the string.
弦的振動產生聲波，而弦的振動頻率跟聲波的頻率相同，但弦波跟聲波的波長及速率卻不同。
常見錯誤：order of bright fringe 亮紋的級數
當order of bright fringe = 2，個screen有及多個bright fringe？
如果您答兩個就是錯的！
正確答案是：2×2+1=5
因爲有bright fringe是有兩邊，而且中間還有一個 zeroth order bright fringe。
DSE Physics 考試 可背LQ Answer
有一年公開試問考生爲何度距離中綫長度要用2nd order bright fringe而不用1st order bright fringe。
相信第一次見到的考生都要想一想，因爲這些是非常practical的實驗手法。
答案是因爲用2nd order bright fringe 的%error會比較細。
當您做實驗的誤差是1cm。那麽假設1st bright fringe是10cm，2nd bright fringe是15cm，那麽這個1cm對哪一個影響較大？
當然是15cm吧！
原理就是這樣
Chapter 17 Reflection of Light
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Light rays 光線
near object
divergent from a point of a near object
來自近距離物體某點的光線為發散
distant object
parallel from a point of an object at infinity
來自遙遠物體上 某點的光線互相平行
Description of reflection 描述反射
- incident ray: light ray striking the boundary
入射線：射向界面的光線、 - reflected ray: light ray leaving the boundary
反射線：離開界面的光線 - normal: construction line perpendicular to the boundary
法線：垂直於界面的虛構線 - angle of incidence: angle between the incident ray and the normal
入射角：入射線與 法線間的夾角 - angle of reflection: angle between the reϐlected ray and the normal
反射角：反射線與法線間的夾角
Laws of reflection 反射定律
- the incident ray, the reϐlected ray and the normal lie on the same plane
入射線、反射線和法線都在同一平面上 - angle of reϐlection r = angle of incidence i
入射角 r = 反射角 i
Regular and diffuse reflection 單向反射與漫反射
Regular reflection 單向反射
parallel incident rays are reϐlected to the same direction
平行入射線朝同一方向反射開去
produces images
產生影像
一句講完，smooth reflecting surface 就會有 image
Diffuse reflection 漫反射
parallel incident rays are reϐlected to different directions
平行入射線朝不同方向反射開去
enables us to see a non-luminous object from different directions
使我們能從不同方向看見不發光體
Mirror images 平面鏡成像
- image distance di = object distance do
像距 di = 物距 do - image size hi = object size ho
像的大小 hi = 物件的大小 ho - laterally inverted image
成像橫向倒置 - virtual image
成像為虛像
Minimum size of mirrors 平面鏡的最小長度
Chapter 18 Refraction of Light
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Refraction of Light 光的折射
Refraction of Light 光折射是光線從一種介質傳播到另一種介質時發生的現象。 當光線從一種介質（如空氣）傳播到另一種介質（如水或玻璃）時，它會改變傳播方向，並且在兩種介質之間發生偏差。 這種偏折是由於光在不同介質中傳播速度不同所引起的。
Refraction 折射
- light travels faster in an optically less dense medium, and slower in an optically denser medium
光在光疏介質的傳播速率較高，在光密介質則較低 - refraction is due to the speed change of light when crossing a boundary
光線在兩種介質中傳播速率不同，因此產生折射- speed ↓, light ray bends towards the normal
速率 ↓，光線 偏向法線 - speed ↑, light ray bends away from the normal
速率 ↑，光線 偏離法線
- speed ↓, light ray bends towards the normal
Laws of refraction 折射定律
the incident ray, the refracted ray and the normal lie on the same plane
入射線、折射線及法線都在同一平面上
Snell’s law 斯涅耳定律
$$n_1 sin\theta_1=n_2 sin\theta_2$$
$$n=\frac{\sin\theta_\text{vacuum}}{\sin\theta_X}=\frac cv$$
$$\frac{n_1}{n_2}=\frac{v_2}{v_1}=\frac{\lambda_2}{\lambda_1}=\frac{\sin\theta_2}{\sin\theta_1}$$
常見錯誤：Measuring the angles 量度入射角和折射角
記住！
角度要貼著normal！！
Critical angle 臨界角 θc
the angle of incidence when the angle of refraction is 90°
當折射角為 90° 時相對應的入射角
$$n=\frac1{\sin\theta_\mathrm{c}}$$
Total internal reflection 全內反射
two conditions 兩個條件：
- the light ray is directed from an optically denser medium to an optically less dense medium
光線從光密介質射向光疏介質（必背！）（公開試經常伏這個位） - angle of incidence > critical angle
入射角 > 臨界角
兩個條件必須 同時滿足，才能產生全內反射。
經典圖： Refracted ray of a ’bent’ stick
「 折曲 」的直棒與折射線
一定要識畫！
Chapter 19 Lenses
這篇文章會向您講解DSE Physics Chapter 19 Lenses 的所有concept
如果您想只在一篇文章就能知道：
- 這一課的重點概念
- 對概念的深度解說
- 考生常見錯誤
這篇文章就正合您心意！
Lens 透鏡是什麽
Lens 透鏡是一種光學元件，常用於光學設備中，例如相機、顯微鏡、望遠鏡等。它是由透明材料（如玻璃或塑料）製成的彎曲表面結構，可以將光線聚焦或分散。透鏡主要依靠光的折射原理來改變光線的方向和焦點。
Convex Lens 凸透鏡
convex lens: central part thicker
凸透鏡：中間部分比邊緣厚
Concave Lens 凹透鏡
concave lens: central part thinner than the edge
凹透鏡：中間部分比邊緣薄
Terms 透鏡的詞彙
- optical centre C: centre of a lens
光心 C：透鏡的中心 - principal axis: line through C; perpendicular to the lens
主軸：通過 C 點，並垂直於透鏡 - focal plane: parallel incident light rays converge to a point or appear to diverge from a point of this plan
焦平面：平行入射光線會聚於其上一點，或看似從其上一點發散出來 - principal focus F: intersection of the focal plane and the principal axis
主焦點 F：焦平面與主軸相交之處 - focal length f : distance CF
焦距 f ：CF 的長度
常問問題：determine focal length
必背答案
Use a screen to capture a sharp image of a distant object. The distance between the screen and the lens is the focal length.
使用螢幕捕捉遠處物體的清晰影像。 螢幕和鏡頭之間的距離就是焦距。
Attach a plane mirror behind the lens and place them in front of an object. The lens or the object is moved until a sharp image is formed alongside the object. The distance between the object and the lens is the focal length.
在鏡頭後面安裝平面鏡並將其放置在物體前面。 移動鏡頭或物體，直到在物體旁邊形成清晰的影像。 物體和鏡頭之間的距離就是焦距。
Real images 實像
- light rays intersect at X
光線在 X 相交 - light rays come from the image position
光線從像的位置發出 - real image is formed at X
光線在 X 的位置形成實像 - real image can be captured by a screen
螢幕可以捕捉真實影像
Virtual images 虛像
- light rays seem to diverge from Y
光線看似從 Y 發散 - no light ray comes from the image position
光線不是從像的位置發出 - virtual image is formed at Y
在 Y 的位置形成虛像 - virtual image cannot be captured by a screen
螢幕無法捕捉虛像
Convex lens 凸透鏡
ray-tracing rules 繪畫光線圖的法則
- a light ray passes straight through C
通過 C 點的光線不會偏折 - parallel to the principal axis → converge to F
與主軸平行 → 會聚至 F 點 - through F′ → parallel to the principal axis
通過 F′ 點 → 與主軸平行
object O, object distance u, image I, image distance v
物體 O、物距 u、影像 I、像距 v
nature of image 影像的本質
| u | v | Image Orientation | Image Type | Image Size |
| ∞ | v | Inverted | Real | Diminished |
| u > 2f | f < v < 2f | Inverted | Real | Diminished |
| u = 2f | v = 2f | Inverted | Real | Same Size |
| f < u < 2f | v > 2f | Inverted | Real | Magnified |
| u = f | ∞ | N/A | N/A | N/A |
| u < f | v > u | Erect | Virtual | Magnified |
Concave lens 凹透鏡
Advantages: increase the field of view
優點：增加視野
ray-tracing rules 繪畫光線圖的法則
a light ray passes straight through C
通過 C 點的光線不會偏折
parallel to the principal axis → appear to diverge from F′
與主軸平行 → 看似從 F′ 點發散
towards F → parallel to the principal axis
指向 F 點 → 與主軸平行
nature of image 影像的本質
- erect, diminished and virtual
正立、虛像、縮小 - The image must be located between the focal plane and the lens
在焦平面與透鏡之間形成
Application of convex lens
- Magnifying glasses
- Glasses for long-sighted eyes
- Cameras
- Microscopes
Application of concave lens
- Door peepholes
- Glasses for short-sighted eyes
- Flashlights
常問問題：Covering part of the lens 遮蓋透鏡
If part of the lens is covered, the whole image can still be seen but it becomes dimmer.
若把部分透鏡遮蓋，我們仍能看到整個像，然而像會變暗。
常見錯誤
直覺而言，把lens遮住一半，影像照道理也會沒了一半。
不過，這個直覺是錯誤的。
Linear magnification 線性放大率 m
$$m=\frac{h_\mathrm{i}}{h_0}=\frac{\nu}{u}$$
for convex and concave lenses 對凸透鏡和凹透鏡而言，
Convex Lens:
| u | m |
| u > 2f | m < 1 |
| u = 2f | m = 1 |
| u < 2f | m > 1 |
Concave Lens:
| u | m |
| All u | m < 1 |
Image size and brightness 像的大小和亮度
The larger the size of the image, the dimmer the brightness of the image.
像越大，像的亮度便越低。
必背原因
曾經有一條PastPaper問過這個concept，以下原因：
As the light energy collected by the lens is the same for both cases, for an enlarged image, same amount of light energy distributed over a larger image. Therefore, the image is dimmer.
由於兩種情況下鏡頭收集的光能相同，因此對於放大的影像，相同量的光能分佈在較大的影像上。 因此，影像較暗。
Lens formula 透鏡公式
$$\frac{1}{f}=\frac{1}{u}+\frac{1}{v}$$
| Object Type | Image Type | Focal Length (f) | Object Position (u) | Image Position (v) |
| Convex | Real | + | + | + |
| Convex | Virtual | + | + | – |
| Concave | Real | – | + | – |
Relationship between focal length and refractive index
larger refractive index = shorter focal length
折射率越大=焦距越短
常見錯誤：Light rays from infinity 無限遠的光線
大量學生只記得聚集在focal length，但應該是聚焦在focal plane
Light rays from different points at inϐinity should focus on different points on the focal length.
不同位置從無限遠入射的光線，會分別聚焦到焦平面不同的點上。
常見錯誤： Sources of light rays 光線的來源
簡單而言，頭駁頭，尾駁尾
常見錯誤：Paths of light ray 光線的路徑
簡單而言，不要點到即止
常見錯誤：Position of the lens 透鏡的位置
For a fixed object– image separation, there are two positions for the lens to form a sharp image. One gives a magnified image and the other one gives a diminished image.
在物體和像的距離固定下，透鏡可在物體和像之間的兩個位置形成清晰的像。當中一個像是放大的，另一個則是縮小的。
Physics 必修課題
- Temperature and Thermometers
- Heat Capacity
- Change of State
- Gas laws and Kinetic Theory
- Motion
- Force
- More about Force
- Work Energy and Power
- Momentum
- Projectile Motion
- Uniform Circular Motion
- Gravitation
- Wave Motion
- Reflection Refraction and Diffraction
- Interference and Stationary Waves
- Light and Sound
- Reflection of Light
- Refraction of Light
- Lenses
- Electrostatics
- Circuit and Power
- AC and Domestic Electricity
- Electromagnetism
- Electromagnetic Induction
- Radiation and Radioactivity
- Rate of Decay and Uses of Radionuclides
- Nuclear Energy