# Newton's and Huygens' Theories of Light (2023)

In the seventeenth century, physicists had a significant debate on trying to explain the phenomenon of light. Christiaan Huygens’ theory of light, which states that light is made of waves, was one of the first well-known theories explaining the behaviour of light. Another theory emerged when Newton tried to disprove the wave theory by publishing his corpuscular theory of light, which states that light is made from small particles.

## What is Newton’s theory of light?

Isaac Newton studied the behaviour of light in his theory of colour. His theory of light was based on his laws of motion, as he thought of light as a straight line motion made out of small particles called corpuscles. Hence Newton’s theory of light is also known as the corpuscular theory. By studying the geometric nature of reflection and refraction of light, Newton concluded that light is composed of coloured particles that combine to appear white.

Reflection is a phenomenon of light that occurs when it impacts a surface that does not fully absorb its radiant energy, resulting in the light bouncing back from the boundary. Fig. 1 - Reflection of light Refraction of light is the bending of light when it passes from one medium to another. This changes the velocity of light depending on the density of the mediums.

(Video) Huygens vs Newton theories of light Zeineb Fozan Fig. 2 - Refraction of light

Check out our explanation, Refraction at a Plane Surface, for more info on refraction.

Newton noticed that reflection and refraction could only be possible if light is made up of particles (or, as he called them, corpuscles). His theory of light states that light continuously emits small particles or corpuscles that seem to change velocity when they pass from one medium to another with different densities. Therefore, the speed of light changes depending on the density of the medium it passes through.

### Wave theory of light: Newton’s prism experiment

Newton conducted an experiment to disprove the wave theory of light and prove that light travels as a flow of particles in a straight line instead of a wave. His experiment explained three main phenomena of light: reflection, refraction, and the rectilinear propagation of light. However, his theory could not explain diffraction, which is a main property of waves.

Newton decided to prove his theory by studying the refraction of light and, more specifically, the colour spectrum that was thought to appear when light passes through glass. He let one beam of sunlight (which is white light) pass through a glass prism. He observed that the light scattered into several colours resembling a rainbow. He named this multicoloured band of light a colour spectrum. Although the colour spectrum was continuous, Newton split the spectrum into seven categories of different colours, namely red, orange, yellow, green, blue, indigo, and violet.

Newton then passed the beam of sunlight through a second prism that was held upside down so that the spectrum passing through the first prism was recomposed into white light (see image1 below). Fig. 3 - Newton's prism experiment and refraction of light

(Video) Newton vs Huygens: corpuscular vs wave models of light explained and refuted

Newton first thought that the colour spectrum was caused by the glass, but through his experiments, he concluded that every colour has a specific angle of refraction. He observed that (a) all objects appear to be the same colour as the beam of coloured light that illuminates them and (b) that a beam of coloured light will stay the same colour no matter how many times it is reflected or refracted. This led him to conclude that colour is a property of the light that reflects from objects and not a property of the objects themselves.

Newton also proposed the existence of the aether, a suggested medium through which light travels. However, the presence of a so-called aether was disproved in the following centuries.

## What is Huygens’ theory of light?

In the late seventeenth century, Christiaan Huygens proved that his wave theory of light could explain the phenomena of diffraction, interference, and reflection. Huygens’ theory states that each point in a source of light sends a wavefront in all directions in a continuous and homogeneous medium called aether.

Diffraction of light is the bending of light around the edges of an object (waves are bent when they encounter the edges of an object).

Interference is the phenomenon that happens when two waves merge, resulting in a higher, lower, or zero amplitude. When waves merge, they create a higher amplitude wave at the points where the two waves meet, creating an interference pattern of bold and faint shadows.

Huygens thought that diffraction occurs due to the interference of the wavefronts and that light waves differ from mechanical or water waves in the direction of travel. Huygens showed that the edges of the shadows of the interference pattern are not perfectly sharp. As a result, Huygens concluded that light must be a wave and diffracts when it passes through an opening.

Huygens’ theory managed to explain refraction and reflection as well as diffraction and the resulting interference pattern. However, Huygens’ theory was partially disproved in the following centuries. Huygens theory states that light travels through a medium in the form of a wavefront, but Maxwell’s theory proposed that light does not require a medium to propagate and can travel through a vacuum. He also assumed that light is formed from interchanging electric and magnetic fields, which travel as waves at the speed of light.

## What is Huygens’ Principle?

Huygens’ principle states that when a light wave travels in a vacuum or a medium and reaches an opening, its wavefront can be considered as individual points emitting new sources of wavelets that expand in all directions, creating s

Huygens’ principle explains the shape that is observed in a wave, such as water waves. It also explains the phenomenon of wave diffraction around edges. Huygens’ principle is now used to develop optics, for example, mirrors and lenses.

### Thomas Young and the double-slit experiment

As Huygens’ principle was never experimentally validated, Newton’s theory prevailed. Thomas Young decided to conduct an experiment that would help prove Huygens’ theory that light is a wave and not a particle. Young believed that light is indeed a wave and should have properties similar to water waves. He also believed that light waves should interact when they meet (and that this interaction should include the waves merging). This is the behaviour that Young was expecting to observe with his experiment.

When two crests of a wave meet, they combine to form a wave that has a larger amplitude. When a crest meets a trough, the waves cancel each other out and form a flat wave or a wave with less amplitude at that point.

(Video) Physics - Newton's corpuscular theory of light - Science

Young placed a light source behind a slit to allow a beam of light to enter through a single point. The light then spread out and entered a second screen with two slits with a screen in the front. Two light sources were required to obtain interference, and Young observed that light spreads out by diffraction at the double-slit. He also observed an interference pattern formed on the screen with bright and dark shadows. Fig. 4 - Double-slit experiment

From this experiment, Young realised that light is a form of a transverse wave because the light behaved exactly as expected (there was an interference pattern with bright and dark shadows indicating the points where two crests and troughs met respectively). If light were indeed a particle, as Newton predicted in his theory of light, then the light beam passing through the slit would have been replicated on the viewing screen, as shown below. Fig. 5 - Diagram showing the experiment where light is replicated on the viewing screen behind two openings

(Video) Newton's and Huygens' Models of Light // HSC Physics

## Affect on the wave-particle duality of light

A century later, Einstein proved that light can also exist as individual particles of energy, similar to what Newton predicted. As a result, both Newton’s and Huygens’ theories were somewhat correct as light behaves as both a wave and a particle. Young’s experiment was also recreated in several variations, including using electrons instead of light beams. This showed that when detectors were used at the slits, the particles seemed to behave as waves.

Many physicists tried to explain the dual behaviour of light, which seems to behave as particles at times and as waves at other times. These experiments and theories led to the development of the modern quantum mechanics theory, which states that light behaves as a particle and a wave, but we can’t observe both properties at the same time.

## Newton’s and Huygens’ Theories of Light - Key takeaways

• Isaac Newton’s theory of light states that light is a straight line motion made out of small particles called corpuscles.

• Huygens’ theory of light states that light is made out of waves.

• Huygens’ theory was partially proven by Thomas Young using the double slits experiment.

• Both theories were proven to be valid as light was later proven to have both wave and particle properties.

• These light theories eventually led to the quantum mechanics dual theory of light.

Images

(Video) 14.07 What is Newton’s Corpuscular theory of light

A Simple Experimental Setup to Clearly Show that Light Does Not Recombine After Passing Through Two Prisms. https://aapt.scitation.org/doi/10.1119/1.5018680

## FAQs

### What is the difference between Huygens theory of light and Newton's theory of light? ›

Sir Isaac Newton proposed that light was made of tiny particles known as photons, while Christian Huygens believed that light was made of waves propagating perpendicular to the direction of its movement.

Who is correct Newton and Huygens? ›

Newton appealed to the "Royal Society", the topmost authority in those bygone times, and 1715 it ruled that Newton's point of view was the correct one. This was not as stupid as it appears now. Huygens, as we know now, was right but could not really prove his assertions then.

What was Newton's theory on light? ›

Newton thought that light was composed of extremely subtle "corpuscles," an idea reflected in the division of light into photons today. His use of multiple prism arrays, described in his Opticks, published in 1702, were arguably some of the initial experiments that led eventually to the development of tunable lasers.

Why was Huygens theory rejected? ›

The reason is that the wave theory was not popular until the end of 18th century. The prevalent theory was corpuscular, and it is hard to give a correct explanation of diffraction within corpuscular theory. (Newton tried).

What are the limitations of Newton's theory of light? ›

Newton's corpuscular theory fails to explain the simultaneous phenomenon of partial reflection and refraction on the surface of transparent mediums such as glass or water. The corpuscular theory fails to explain optical phenomena such as interference, diffraction, polarization, etc.

What does Huygens principle tell us about light? ›

Huygens stated that light is a wave propagating through space like ripples in water or sound in air. Hence, light spreads out like a wave in all directions from a source.

Is the Newtonian theory correct? ›

That universal law of gravitation worked pretty well for predicting the motion of planets as well as objects on Earth — and it's still used, for example, when making the calculations for a rocket launch. But Newton's view of gravity didn't work for some things, like Mercury's peculiar orbit around the sun.

What did Huygens theory not explain? ›

Huygens's waves theory could not illustrate double refraction because the light is perceived as a mechanical wave in Huygens's theory, which can not explain double refraction. When an unpolarized light beam strikes certain materials, such as Quartz or Calcite crystal, it splits into two refracted beams.

Why did Newton's corpuscular model of light fail? ›

1. Newton's corpuscular theory fails to explain simultaneous phenomenon of partial reflection and refraction on the surface of transparent medium such as glass or water. 2. The corpuscular theory fails to explain optical phenomena such as interference, diffraction, polarization etc.

When was Newton's theory of light? ›

Isaac Newton's reputation was initially established by his 1672 paper on the refraction of light through a prism; this is now seen as a ground-breaking account and the foundation of modern optics.

### How were Huygens and Newton's ideas different? ›

Christian Huygens

Huygens focussed on the observations that light would create diffraction and interference patterns. He proposed that light consisted of waves, which was able to explain diffraction and interference. Newton's theory was unable to do this.

Why is Huygens principle correct? ›

The wave equation of quantum mechanics is first order in the time; therefore, Huygens' principle is correct for matter waves, action replacing time."

Who disproved Newton's corpuscular theory? ›

Euler also rejected Newton's essentially corpuscular theory of the nature of light by explaining optical phenomena in terms of vibrations in a fluid ether.

What are the main issues with Newton's method? ›

Failures of Newton's Method
• At one of the approximations xn, the derivative f′ is zero at xn, but f(xn)≠0. As a result, the tangent line of f at xn does not intersect the x-axis. ...
• The approximations x0,x1,x2,… may approach a different root. ...
• The approximations may fail to approach a root entirely. In Example 4.8.
Nov 9, 2020

What was the problem with Newton's law? ›

The second problem with Newton's theory was that it described gravity as an instantaneous force of attraction between two massive objects. Consequently, if you move one of them, the other knows about the move immediately due to the change in gravitation, irrespective of the distance between them.

Where does Newtonian physics fail? ›

But there are two instances where Newtonian physics break down. The first involves objects traveling at or near the speed of light. The second problem comes when Newton's laws are applied to very small objects, such as atoms or subatomic particles that fall in the realm of quantum mechanics.

Is Newtonian physics still valid? ›

Newtonian physics continues to be applied in every area of science and technology where force, motion, and gravitation must be reckoned with. However, today's physicists, unlike Newton, know that his laws do not work in all circumstances.

How accurate is Newtonian physics? ›

Newtonian Mechanics is accurate enough for day-to-day calculations. Where Newtonian mechanics becomes inaccurate is in the very small, Quantum world or the very fast, where Special Relativity effects dominant. At very large scales, the generalised formulation of Spec.

What are the limitations of Newtonian relativity? ›

There are two limitations on classical mechanics. First, speeds of the objects should be much smaller than the speed of light, v ≪ c, otherwise it becomes relativistic mechanics. Second, the bodies should have a sufficiently large mass and/or kinetic energy.

Why did Huygens believe light was a wave? ›

Huygens believed that ether vibrated in the same direction as light and formed a wave itself as it carried the light waves. In a later volume, Huygens' Principle, he ingeniously described how each point on a wave could produce its own wavelets, which then add together to form a wavefront.

### Why did Newton think light was a particle? ›

Light travels in a straight line, and therefore it was only natural for Newton to think of it as extremely small particles that are emitted by a light source and reflected by objects. The corpuscular theory, however, cannot explain wave-like light phenomena such as diffraction and interference.

Why was Newton's theory of light the dominant theory for so long? ›

Although the wave theory made a strong case, Newton's particle theory dominated for much of the following century. This dominance was due largely to Newton's undoubted successes in other scientific areas, including studies of gravity, which gave him immense prestige within the scientific community.

Did Newton Think light had mass? ›

Around 1700 the great Newton, who founded the laws of mechanics on 3 principles and the universal law of gravitation, supposed that light was made up of small particles. These light particles as any other particle, he supposed, would naturally have mass too.

What are the similarities between Newton's theory of light and Huygens principle? ›

The Newton corpuscular theory and Huygens wave theory both theories gives the explanation of the nature of light. According to Huygens wave theory the light was made up of wave not a particle. But by the prism experiment considered by Newton's corpuscular theory it is clear that light has small particles.

Who proved the theory of light? ›

The most prominent advocate of a particle theory of light was Isaac Newton. Newton's careful investigations into the properties of light in the 1660s led to his discovery that white light consists of a mixture of colours.

How does the Huygens principle prove law of reflection? ›

Proof of Reflection

Following Huygen's principle, every point on AA' will act as a source of secondary wavelets. Hence, the angle of incidence and angle of reflection are both equal. This is also stated by the first law of reflection.

What are the two limitations of Huygens wave theory? ›

The limitations of Huygens Wave Theory of Light are as follows: It could not explain rectilinear propagation of light. It could not explain phenomenon of polarisation of light and phenomenon like Compton Effect, photoelectric effect.

Which of the following can be proved using Huygens principle? ›

Huygen's Principle Definition: Every point on a wavefront is a source of wavelets. These wavelets spread out in the forward direction, at the same speed as the source wave. The new wavefront is a line tangent to all of the wavelets.

What was Newton's mistake in concluding that light was corpuscular? ›

If light were a corpuscle, as Newton would have it, it would simply travel in a straight line through space. But if light were a wave, it would have to interfere and diffract when it encountered a barrier, a slit, or an "edge" to a surface.

Is corpuscular theory correct? ›

A major prediction of the corpuscular theory is that the speed of light in a denser medium is more than the speed of light in a rarer medium. The truth is that the speed of the light is smaller in a denser medium. Therefore, Newton's corpuscular theory is wrong.

### What are the 2 theories of light? ›

The two most successful theories of light were the corpuscular (or particle) theory of Sir Isaac Newton and the wave theory of Christian Huygens. Newton's corpuscular theory stated that light consisted of particles that travelled in straight lines.

What are the different theories of light explain each theory? ›

Light can be explained in two ways. The wave theory and the corpuscular theory were suggested in the seventeenth century as opposing views of light's nature. Wave theory of light: Huygens suggested that light has a wave character and that it travels in a medium called ether as a longitudinal wave.

What is the difference between wave theory and particle theory of light? ›

1. Particle theory: Light consists of a stream of small particles, because it travels in straight lines at great speeds is reflected from mirrors in a predictable way. 2. Wave theory: Light is a wave, because it undergoes diffraction and interference (Young's double–slit experiment).

What is the difference between reflection and refraction according to Huygens? ›

As we know that when light falls on an object, it bends and move through the material, this is what refraction is. Also when the light bounces off the medium it is called a reflection.

What are the two main theories of light? ›

The two most successful theories of light were the corpuscular (or particle) theory of Sir Isaac Newton and the wave theory of Christian Huygens. Newton's corpuscular theory stated that light consisted of particles that travelled in straight lines.

Which theory of light came first? ›

In his Traité de la Lumière (1690; “Treatise on Light”), the Dutch mathematician-astronomer Christiaan Huygens formulated the first detailed wave theory of light, in the context of which he was also able to derive the laws of reflection and refraction.

What are the two laws of light? ›

(i) The incident ray, the reflected ray and the normal ray at the point of incidence, lie in the same plane. (ii) The angle of incidence is equal to the angle of reflection.

Which theory proved that light is a particle? ›

Around 1700, Newton concluded that light was a group of particles (corpuscular theory).

Which phenomenon support only the wave theory of light? ›

Wave theory of light explains the phenomena of interference, diffraction, scattering, dispersion, polarisation etc.

Why wave theory of light could not explain? ›

Huygen's wave theory of light cannot explain the photoelectric effect. Because it is due to particle nature of light. Was this answer helpful?

### How do you use Huygens principle to explain Snell's law? ›

Note: According to Snell's law the ratio of sine of angle of incidence to the sine of angle of refraction is equal to the ratio of refractive index of second medium to the first medium. Huygen's principle tells us that each point on a wavefront is a source of secondary waves, which add up to later wavefronts.

What is law of refraction with Huygens principle? ›

Huygen's principle states that every point on a wavefront behaves as a source for secondary waves, whose common tangent (envelop) becomes the new wavefront. Using this principle, let's prove Snell's law of refraction - Ratio of the sine of angle of incidence to the sine of the angle of refraction is a constant.

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