Hukum Kekekalan Energi Mekanik

aplikasi energi mekan

Hukum kekekalan Enegi Mekanik berbunyi Pada sistem yang terisolasi (hanya bekerja gaya berat dan tidak ada gaya luar yang bekerja) selalu berlaku energi mekanik total sistem konstan. Pada posting tentang macam-macam bentuk energi diantaranya adalah energi potensial dan energi kinetik.

Energi total yang dimaksud pada hukum kekekalan energi mekanik adalah jumlah antara energi potensial dengan energi kinetik.

Energi potensial

Energi potensial adalah energi yang dimiliki benda karena kedudukannya. Energi ini tersembunyi pada benda tetapi bila di beri kesempatan energi ini bisa di manfaatkan contoh misalnya energi potensial pada pegas yang ditarik terjadi juga pada pada karet atau busur panah. Contoh yang kedua adalah Energi potensial gravitasi yaitu energi yang dimiliki benda yang disebabkan oleh ketinggian terhadap suatu titik acuan tertentu.

Besar energi potensial gravitasi sebanding dengan massa, percepatan gravitasi serta ketinggian

Ep = m g h

Keterangan

• m=massa(kg)
• g=percepatan gravitasi(m/s²)
• h=ketinggian(m)

Energi Kinetik

Energi kinetik adalah energi yang dimiliki benda karena geraknya misalnya anak panah yang lepas dari busur memiliki kecepatan dan massa tertentu maka anak panah tersebut memiliki energi kinetik yang besarnya berbanding lurus dengan massa serta kecepatan kuadrat.  Dalam persamaan

Ek = ½ mv²

Keterangan

• Ek= energi kinetik(Joule)
• m=massa(kg)
• v=kecepatan(m/s)

Energi Mekanik

Energi mekanik adalah jumlah total dari energipotensial dengan energi kinetik atau

Em= Ep + Ek

Menurut hukum kekekalan energi mekanik bahwa jumlah energi mekanik selalu tetap dengan syarat tidak ada gaya luar yang bekerja pada sistem.

Em₁ =Em₂

Ep₁ + Ek₁ = Ep₂ + Ek₂

m g h₁ + ½ mv₁² = m g h₂ + ½ mv₂²

Penerapan hukum kekekalan energi mekanik adalah pada kasus benda jatuh dipermukaan bumi atau berada dalam medan gravitasi bumi. Berhubungan dengan hukum kekekalan energi mekanik dapat disimpulkan.

1. Pada kedudukan awal, kelajuan sama dengan nol sehingga Ek=0, s atau gerak jatuh bebas.  Sedangkan energi potensial Ep mencapai nilai maksimum, sama dengan energi mekaniknya.
2. Pada keadaan selanjutnya, energi potensial berkurang dan berubah menjadi energi kinetik. Pada setengah perjalananya, besar energi potensial sama dengan energi kinetik.
3. Pada saat menyentuh tanah (bidang acuan), seluruh energi potensial berubah menjadi energi kinetik sehingga energi potensialnya Ep=0, sedangkan energi kinetik Ek= mencapai nilai maksimum, sama dengan energi mekaniknya.

Energi potensial, energi kinetik serta energi kinetik merupakan besaran skalar sama halnya dengan usaha oleh karena dimensi serta satuannya juga sama.

Demikian posting yang membahas tentang hukum kekekalan energi mekanik, semoga bermanfaat kurang lebihnya tuliskan di kolom komentar.

Newton's Second Law

"Change of motion is proportional to the force applied, and take place along the straight line the force acts."

Newton's second law for the gravity force - weight - can be expressed as

F = m g         (1)
where
F = force (weight)
m = mass
g = acceleration of gravity

The force caused by gravity - g - is called weight. Note! Mass - m - is a property.
The acceleration of gravity can be observed by measuring the change of velocity of a free falling object:

g = dv / dt         (2)
where
dv = change in velocity
dt = change in time

A dropped object accelerate to a speed of 9.81 m/s or 32.174 ft/s in one second.

Acceleration of Gravity in SI Units

g = 9.81 m/s²

Acceleration of Gravity in Imperial Units

g = 32.174 ft/s²

Velocity and Distance Traveled of a Free Falling Object

The velocity of a free falling object can be expressed as:

v = g t         (3)
where
v = velocity

The distance traveled by a free falling object can be expressed as:

s = 1/2 g t²         (4)
where
s = distance traveled by the object

The velocity and distance traveled by a free falling object:

Time (s)	Velocity				Distance
	m/s	km/h	ft/s	mph	m	ft
1	9.8	35.3	32.2	21.9	4.9	16.1
2	19.6	70.6	64.3	43.8	19.6	64.3
3	29.4	106	96.5	65.8	44.1	144.8
4	39.2	141	128.7	87.7	78.5	257.4
5	49.1	177	160.9	110	122.6	402.2
6	58.9	212	193.0	132	176.6	579.1
7	68.7	247	225.2	154	240.3	788.3
8	78.5	283	257.4	176	313.9	1,029.6
9	88.3	318	289.6	198	397.3	1,303.0
10	98.1	353	321.7	219	490.5	1,608.7

Note! The velocity is achieved without any aero-dynamical resistance (vacuum). The air resistance will be significant for higher velocities or for object with large surface area to mass ratio - feathers or similar.

Newton's First Law

"Every body continues in a state of rest or in a uniform motion in a straight line, until it is compelled by a force to change its state of rest or motion."

Newton's Third Law

"To every action there is always an equal reaction - if a force acts to change the state of motion of a body, the body offers a resistance equal and directly opposite to the force."

Common Expressions

• superimposed loads: kN/m²
• mass loads: kg/m² or kg/m³ 
• stress: N/mm²
• bending moment: kNm
• shear: kN

1 N/mm = 1 kN/m

1 N/mm² = 10³ kN/m²

1 kNm = 10⁶ Nmm

Belajar Fisika - Gaya Bollard

Bollards ini biasa terjadi pada dermaga dan digunakan ketika mooring kapal dan perahu. Bollards is common on quays and are used when mooring ships and boats.

Kekuatan usaha dalam tali dapat dihitung

The effort force in a rope can be calculated

S = F e^-μα         (1)
where
S = effort force in the rope (N)
F = load (N)
e = 2.718..
μ = friction coefficient (approximately 0.3 - 0.5 is common for a rope around a steel or cast iron bollard) 
α = angle where the rope is in contact with the bollard (radians)

Angle - turns, degrees and radians

• 1/4 turn : 90 degrees => α = 1/2 π
• 1/2 turn : 180 degrees => α = π
• 1 turn : 360 degrees => α = 2π
• 2 turns : 720 degrees => α = 4π

Example - A rope with one turn around the bollard 

Contoh - Sebuah tali dengan satu putaran sekitar tonggak

With a friction coefficient of 0.5 the effort force in the rope can be calculated as 

Dengan koefisien gesekan sebesar 0,5 upaya paksa dalam tali dapat dihitung sebagai

S = F e^{-0.5 2π}
    = 0.043 F (N)

As we can see - one turn around the bollard reduces the required effort force to less than 5% of the load.

Example - Shoring a ship

The retardation (negative acceleration) of a ship arriving at quay with velocity 0.05 m/s and stopped within 2 seconds, can be calculated as

a = dv/dt         (2)

= (0.05 m/s) / (2 s)
= 0.025 (m/s²)

With a mass of 20000 kg the required force F in the rope from the ship can be calculated as

F = m a         (3)

= (20000 kg) (0.025 m/s²)
= 500 N

The required effort force with a half turn around a bollard with a friction coefficient of 0.4 can be calculated as

S = F e^{-0.5 2π}

= (500 N) e^{-0.4 π}
= 142 (N)  

The Effort Force - Load Force ratio for various rope angles are indicate in the chart below:

• friction coefficient 0.5

Flash Animations for Physics

We have been increasingly using Flash animations for illustrating Physics content. This page provides access to those animations which may be of general interest. The animations will appear in a separate window.

The animations are sorted by category, and the file size of each animation is included in the listing. Also included is the minimum version of the Flash player that is required; the player is available free from http://get.adobe.com/flashplayer/. The categories are:

• Chaos
• Classical Mechanics
• Electricity and Magnetism
• Fluid Mechanics
• Micrometer Caliper
• Miscellaneous
• Nuclear
• Optics
• Oscilloscope
• Quantum Mechanics
• Relativity
• Sound Waves
• Vectors
• Waves

In addition, I have prepared a small tutorial in using Flash to do Physics animations. It contains screen shots and embedded Flash animations, so the file size is a 173k. You may view it in a separate window at http://faraday.physics.utoronto.ca/PVB/Harrison/Flash/Tutorial/FlashPhysics.html.
LInks to versions of these animations in other languages, other links, and license information appear towards the bottom of this page.

Reference:
http://www.upscale.utoronto.ca/GeneralInterest/Harrison/Flash/

Physic Is Fun

These videos will help show the lighter side of physics with amazing experiments, funny raps and explanations of concepts in terms students can understand.

1. Musical Tesla Coil: Check out this video to hear the amazing noises the high-voltage sparks emitted by this Tesla coil produce.
2. Large Hadron Collider Rap: Have some fun with this great rap video about CERN’s hadron collider.
3. How Superconducting Levitation Works: Think levitation is impossible? This video will show you otherwise using magnets.
4. Fun with Ferrofluid: See the bizarre ferrofluid in action in this video and what effect magnets have on it.
5. Water Droplets in Zero Gravity: This video shows you an experiment done on the International Space Station, letting you see how water acts in a low gravity environment.
6. Sound Waves on Fire: You may not be able to see sound waves normally, but in this video they’re more than evident.
7. Halo of Water Vapor Appears Around Supersonic F-14 Jet: See what effect breaking the sound barrier has on water condensation through this video.
8. Helium Superfluid: What happens when you get helium into a liquid form? Watch this video to find out.
9. Boomerang in Zero Gravity: No matter where you go, a boomerang will always come back as this video filmed in space shows.
10. Mythbusters Play with Sulfur Hexafluoride: In this short but fun video, you’ll see the effect different gasses have on vocal sounds.
11. The Physics of Superheroes: Watch this video to have superheroes explained using real life physics concepts.
12. The Physics of Baseball: Get a more concrete and fun explanation of physics concepts by seeing them applying to baseball in this video.

Physics Basics

Learn the essentials of understanding physics through these instructional videos for students at all levels.

13. Photons: Corpuscles of Light: You may be wondering what the heck a corpuscle is, but you’ll learn soon enough when you watch this video.
14. Fits of Reflection and Transmission – Quantum Behaviour: Check out this video to have quantum physics explained by Richard Feynman.
15. Electrons and Their Interactions: Another video lecture given by Feynman helps gives some clarity to the way particles interact with one another.
16. Polarization: Physics professor Walter Lewin explains polarization, rainbows, smoke and sunsets in this video that even elementary students can understand and appreciate.
17. The Wonders of Electricity and Magnetism:Walter Lewin is back in this video, showing off some fun experiments in order to explain the bigger physical properties behind them.
18. Atoms and Heat: Here, Professor Richard A. Mueller of UC Berkeley explains the fundamentals of applying heat to atoms.
19. ForceMan: While created with kids in mind, this video is a fun way to learn about the physics of force for all ages.
20. Planetary Forces Rap: Make learning about planetary forces a little more fun and easier to remember with this clever rap.
21. Speed of Light: This video uses a microwave and some eggs to teach students about the speed of light.
22. Classical Mechanics: This video from MIT will give you a good primer in the basics of Newtonian physics.
23. Fundamentals of Physics: If you want something a little more in-depth, you can check out this lecture series from Yale to get a crash course in physics fundamentals.
24. Vibrations and Waves: Give this lecture series a try to learn about a wide range of topics related to vibrations and waves–from sunsets to musical instruments.
25. Electricity and Magnetism: Through these video lectures you’ll build a strong foundation of knowledge in how electricity and magnetism work in the world.
26. The Mystery of Light: Starting with the basics, this video will engage you in exploring the special properties of light.

Experiments and Demonstrations

Few things make an abstract concept clearer than seeing how it works in real life. These videos will do just that, making things like light, motion and friction easier to understand.

27. Double-Slit Electron Experiment: In this video you’ll see an experiment that demonstrates both the wave and particle properties of light and other quantum particles.
28. Galileo’s falling bodies experiment re-created at Pisa: Go back to physics basics in this video that recreates the famous experiment done by Galileo to illustrate ideas of mass, inertia and gravity.
29. Millikan Oil Drop Experiment: Learn how Millikan did his famous experiment and understand the meaning of it all by watching this great animated clip.
30. Isaac Newton’s decomposition of sunlight with a prism: Light may look white or colorless, but this experiment with prisms will expose its true nature.
31. Interference and Diffraction of Light Experiment: Get a look at some of the most amazing properties of light in this high-tech experiment.
32. Cavendish’s torsion-bar experiment: Learn how the gravitational constant (or G) was first calculated using a simple experiment in this video.
33. Eratosthenes calculates Earth’s circumference: How did a man living in ancient times manage to fairly accurately figure out the circumference of Earth? Watch this video to find out.
34. The Inclined Plane: This fun, if a little retro, video shows how distance and force are affected by an inclined plane.
35. The Rutherford Experiment: Check out this video to see how the parts of an atom were discovered from Professor Harman at the U of Virginia.
36. Foucault Pendulum: Want to see Earth’s rotation in action? Watch this video for more info.

Perfect for the Classroom

If you’re trying to teach students, or if you’re the student yourself, these videos can go a long way towards illustrating concepts in a fun, informative way.

37. Atoms: The Space Between: Here you cannot only watch a great video on the structure of atoms, but will get accompanying explanations and class materials as well.
38. Light Particles Acting Like Waves: This video attempts to make the behavior of light a little more clear for students (and yourself).
39. Quantum Mechanics: Quantum mechanics can be a tough subject to learn, let alone teach, so get some help from this excellent PBS produced video.
40. Strings to the Rescue: Through this video, you’ll be able to better teach and learn about string theory and Einstein’s late-in-life work.
41. That’s My Theory!: This game will quiz you or your students on which scientist held which physics theory.
42. Gravity: The Odd Man Out: This NOVA video will add on to your understanding of string theory by explaining the strong and weak nuclear forces.
43. Beautiful Physics: This video series from Teachers.tv offers fun, inspiring ways to look at fundamental physics concepts.
44. The Building Blocks of Matter: Try out this video for a great explanation of what the Large Hadron Collider is and what it is designed to figure out.
45. Physics Demo Videos: No matter what principle you’re trying to explain in class, you’ll find a great corresponding demo video here.
46. The Wonders of Physics: In this video series by Professor Clint Sprott you’ll get a fun and almost circus-like look at physics which can keep even the most physics-phobic students engaged.

Television Programs

Check out these excellent TV programs and series to learn more about physics.

47. The Elegant Universe: This three-part mini-series from NOVA explains the physics of the universe.
48. Carl Sagan’s Cosmos: Sagan’s series may be old, but much of the data it presents still holds true and it can be a wonderful program to learn about the beauty and the mystery of the Cosmos as we know it.
49. Absolute Zero: This episode of NOVA gets chilly, with discussions of Absolute Zero and how to get there.
50. Wright Brothers’ Flying Machine: Get a better idea of how flight, even the earliest ones, actually works in this episode of NOVA.
51. The Universe: Learn more about our home solar system, galaxy and the universe beyond in this great series.
52. Black Holes: The Other Side of Infinity: Use this video as a chance to teach and learn more about black holes.
53. Cosmic Journeys: This television series will help you to learn more about space exploration and what we’ve garnered from it.
54. Wired Science: You’ll find all kinds of physics and general science videos in this helpful series.
55. Milestones in Science and Engineering: This series of videos will explain things like manned flight, the phonograph, cathode-ray tubes and more.
56. How Long Is A Piece Of String?: It may seem like a simple question but this physics-focused show demonstrates that true length is a much more complex matter.
57. Monster of the Milky Way: How much do you know about the black hole that is theorized to lie at the center of our galaxy? This video is a great primer on the subject.

Documentaries

These documentaries address some of the major questions in physics and entertain while they educate.

58. The Quantum Revolution: In this video, physicist Michio Kaku explores where physics may be headed in the coming decades.
59. Cold Fusion: Fire from Water: Through this movie you can learn about the potential of this source of energy.
60. Uncertainty Principle: This short film will fill you in on quantum mechanics and Einstein’s surprising dislike for the subject.
61. ATOM: Nuclear physicist Professor Jim Al-Khalili explores the history, present and future of the atom in this mini-series.
62. Exploring Einstein: Life of a Genius: Watch this video to learn more about the life and work of one of the greatest thinkers of our time.
63. The Atom Smashers: This film follows the scientists at Fermilab for a little over a year as they hunt for the mysterious and elusive Higgs boson particle.
64. Stephen Hawking and the Theory of Everything: Take a look at this short film to better understand the work of famed cosmologist Stephen Hawking.
65. Time Trip: Those intrigued by the idea of time travel will love this film that takes a look at the sometimes zany but always scientifically rooted attempts at discovering how to travel through time.
66. The Pleasure of Finding Things Out: Filmed in 1981, this film follows Richard Feynman as he talks about his life, his work and physics in general.
67. The Secret Life of Chaos: In this video, you’ll learn more about the real Chaos Theory that most people only know from a reference in the movie Jurassic Park.

Explaining and Illustrating Concepts

These lectures and videos focus on explaining or elaborating on more specific concepts in physics, both at a basic and more advanced level.

68. Particles, Protons and Quarks: In this question and answer session, you’ll hear Professor Jerome Friedman talk about the atom during a tour of the MIT Museum.
69. Monsters, Dwarfs and Everything In-Between: Astronomer Sally Baliunas talks about the ways in which physics enables scientists to study the wide range of stars in the universe in this video.
70. The Birth and Death of Stars: In this video, Walter Lewin gives an excellent and easily understood lecture on where stars come from and where they go when they die.
71. The Origin of Mass and the Feebleness of Gravity: Try out this lecture where theoretical physicist Frank Wilczek shares his expertise on the origins of mass.
72. String Theory, Black Holes and the Fundamental Laws of Nature: If you’re looking for a great overview of physics topics, this lecture from Andrew Strominger at Harvard is a treat.
73. Spooky Actions at a Distance: Spooky actions aren’t spooky in the way we usually understand the term to mean, as you’ll learn from watching this informative lecture at Princeton.
74. Elliptical Orbits: In this video from a course on classical mechanics, you’ll learn the basics of elliptical orbits and the laws of motion.
75. The Second Law of Thermodynamics and Entropy: Check out this lecture for an in-depth explanation of entropy that is perhaps best suited for more advanced physics students.
76. Torque: Take a closer look at some of Newton’s work in this excerpt from a course given at Yale.
77. The Physical World: Explore the world around you using physics with a little help from this free iTunesU video.
78. The Second Law and Cosomology: This video expands on the basics of entropy and asks some tough questions about how it’s applied to the study of the universe.
79. Quantum gravity in three dimensions: Get an ivy league discussion of quantum gravity through this video.

Cutting-Edge Research

Keep up with new work that’s being done in physics through these inspiring lectures.

80. Lisa Randall: String Theory and Multiple Dimensions: Lisa Randall, a professor at Harvard, discusses the possibility of multiple dimensions in space in this incredibly interesting lecture.
81. Frank Wilczek: Mass, Ether, and the Unification of Forces: Hear from Nobel Prize-winning physicist Frank Wilczek as he discusses his life and his work in this video.
82. New Queries: See where physics is headed in the coming decades in this video.
83. A New Kind of Science: Stephan Wolfram talks about the exciting prospects for using computers to map out our universe in this video.
84. Matchsticks, Scramjets, and Black Holes: Numerical Simulation Faces Reality: Elaine Oran gives listeners and insight into the gap that sometimes occurs between what should happen and what does happen when it comes to science.
85. John Ochsendorf: Redesigning Communities and Carbon Neutrality: Learn more about how science can be applied to technologies that help the world in this lecture.
86. X-rays from comets: a surprising discovery: Learn about a discovery that shocked scientists, that comets actually emit X-rays, in this great video.
87. The Black Hole at the Center of Our Galaxy: Check out this video to learn about the research that’s being done about the black hole that scientists think lies at the heart of our own Milky Way.
88. Loop Quantum Gravity: In this lecture by Carlo Rovelli you’ll learn more about this interesting and engaging theory devised by the speaker himself.
89. Transitioning from the Space Shuttle to the Constellation System: William Gerstenmaier has worked at NASA for over 30 years and shares his thoughts on addressing problems and issues with space travel that have cropped up in recent years.
90. Bose-Einstein Condensates: The Coldest Matter in the Universe: Learn about how theory led to discovery and a whole new way of looking at matter in this lecture.

Engaging Lectures

These lectures capture scholars, thinkers, and the world’s greatest physicists as they discuss a wide variety of topics.

91. Michio Kaku: Physics of the Impossible: Only a few centuries ago, many of the things we use everyday were seen as impossibilities of science. This video lecture discusses how, in the future, things like time travel may become less of a science fiction and more of a reality.
92. 20th Century Physics: In this lecture you’ll learn more about the evolution of science and religion.
93. A Universe from Nothing: Through this lecture you’ll hear from Lawrence Krauss on where our universe came from and where it will end up.
94. Observing the Birth of the Universe: Learn more about the Big Bang in this Princeton lecture given by Professor Lyman Page.
95. Who Needs Physics?: Why bother learning physics? This lecture explains how understanding physics could help us learn about the true nature of the universe.
96. Forty years of high energy string collisions: Hear from scientists at CERN on the history and future of string theory physics in this discussion video.
97. What is the simplest quantum field theory?: If you want to know more about this topic, then the scientists giving this talk at CERN are the best people to learn from.
98. The Universe is a Strange Place: Get inspired by the beauty, paradox and, yes, sometimes strangeness of our universe in this talk from Frank Wilczek.
99. Stephen Hawking asks big questions about the universe: In this TED lecture, Professor Hawking asks some of the most important and nagging questions about our universe, including where it all began and whether or not we are alone in the universe.
100. Challenge in Astrophysics: Physicist Sarah Bridle talks about the new work being done using gravity to map out the universe and the challenges that will still test scientists in the coming years.

Newton's Laws - Chapter Outline

Lesson 1: Newton's First Law of Motion

1. Newton's First Law
2. Inertia and Mass
3. State of Motion
4. Balanced and Unbalanced Forces

Lesson 2: Force and Its Representation

1. The Meaning of Force
2. Types of Forces
3. Drawing Free-Body Diagrams
4. Determining the Net Force

Lesson 3 : Newton's Second Law of Motion

1. Newton's Second Law
2. The Big Misconception
3. Finding Acceleration
4. Finding Individual Forces
5. Free Fall and Air Resistance
6. Double Trouble (a.k.a., Two Body Problems)

Lesson 4 : Newton's Third Law of Motion

1. Newton's Third Law
2. Identifying Action and Reaction Force Pairs

Cahaya

Cahaya adalah energi berbentuk gelombang elekromagnetik yang kasat mata dengan panjang gelombang sekitar 380–750 nm.^[1] Pada bidang fisika,

1. cahaya adalah radiasi elektromagnetik, baik dengan panjang gelombang kasat mata maupun yang tidak. ^[2][3]
2. Cahaya adalah paket partikel yang disebut foton.

Kedua definisi di atas adalah sifat yang ditunjukkan cahaya secara bersamaan sehingga disebut "dualisme gelombang-partikel". Paket cahaya yang disebut spektrum kemudian dipersepsikan secara visual oleh indera penglihatan sebagai warna. Bidang studi cahaya dikenal dengan sebutan optika, merupakan area riset yang penting pada fisika modern.
Studi mengenai cahaya dimulai dengan munculnya era optika klasik yang mempelajari besaran optik seperti: intensitas, frekuensi atau panjang gelombang, polarisasi dan fase cahaya. Sifat-sifat cahaya dan interaksinya terhadap sekitar dilakukan dengan pendekatan paraksial geometris seperti refleksi dan refraksi, dan pendekatan sifat optik fisisnya yaitu: interferensi, difraksi, dispersi, polarisasi. Masing-masing studi optika klasik ini disebut dengan optika geometris (en:geometrical optics) dan optika fisis (en:physical optics).
Pada puncak optika klasik, cahaya didefinisikan sebagai gelombang elektromagnetik dan memicu serangkaian penemuan dan pemikiran, sejak tahun 1838 oleh Michael Faraday dengan penemuan sinar katode, tahun 1859 dengan teori radiasi massa hitam oleh Gustav Kirchhoff, tahun 1877 Ludwig Boltzmann mengatakan bahwa status energi sistem fisik dapat menjadi diskrit, teori kuantum sebagai model dari teori radiasi massa hitam oleh Max Planck pada tahun 1899 dengan hipotesa bahwa energi yang teradiasi dan terserap dapat terbagi menjadi jumlahan diskrit yang disebut elemen energi, E.
Pada tahun 1905, Albert Einstein membuat percobaan efek fotoelektrik, cahaya yang menyinari atom mengeksitasi elektron untuk melejit keluar dari orbitnya. Pada pada tahun 1924 percobaan oleh Louis de Broglie menunjukkan elektron mempunyai sifat dualitas partikel-gelombang, hingga tercetus teori dualitas partikel-gelombang.
Albert Einstein kemudian pada tahun 1926 membuat postulat berdasarkan efek fotolistrik, bahwa cahaya tersusun dari kuanta yang disebut foton yang mempunyai sifat dualitas yang sama. Karya Albert Einstein dan Max Planck mendapatkan penghargaan Nobel masing-masing pada tahun 1921 dan 1918 dan menjadi dasar teori kuantum mekanik yang dikembangkan oleh banyak ilmuwan, termasuk Werner Heisenberg, Niels Bohr, Erwin Schrödinger, Max Born, John von Neumann, Paul Dirac, Wolfgang Pauli, David Hilbert, Roy J. Glauber dan lain-lain.
Era ini kemudian disebut era optika modern dan cahaya didefinisikan sebagai dualisme gelombang transversal elektromagnetik dan aliran partikel yang disebut foton. Pengembangan lebih lanjut terjadi pada tahun 1953 dengan ditemukannya sinar maser, dan sinar laser pada tahun 1960. Era optika modern tidak serta merta mengakhiri era optika klasik, tetapi memperkenalkan sifat-sifat cahaya yang lain yaitu difusi dan hamburan.