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Turning Points in Physics

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A turning point in physics is when a scientist made a revolutionary discovery or development that affected physics so that many things accepted before the discovery were then seen as incorrect or uncertain. Learning about turning points is essential to see how physics has changed and to appreciate science from a historical viewpoint.

What are the turning points in physics?

Turning points in physics include the discovery of the electron, wave-particle duality, and special relativity. All three turning points have left a big mark on both physics and science in general.

Discovery of the electron

During the 1880s and 90s, scientists searched cathode rays for the carrier of charge in matter. Their efforts resulted in the discovery of the electron by J. J. Thomson in 1897. Thomson directed the cathode rays through two parallel metal plates to the glass end of a tube. The rays went down when the upper aluminium plate was negative and up when it was positive. The deflection reflected the potential difference between the plates. Cathode rays were clearly negatively charged particles based on magnetic and electric deflections. Thomson discovered the granularity of electricity, which explains how individual particles carry a charge.

• The idea of a homogenous atom particle was disproved.

• The existence of subatomic particles was proved.

• Daltons atomic theory assumption that atoms were indivisible was disproved.

Wave-particle duality

Wave-particle duality was born from the work of many scientists such as Max Planck, Albert Einstein, Louis de Broglie, Erwin Schrödinger, Niels Bohr, and Arthur Compton. In quantum physics, wave-particle duality states that each particle or quantum phenomenon may be represented as a particle or a wave. This theory gave rise to major discoveries, such as:

• A differential equation that describes how a wave function can explain all aspects of the behaviour of light and matter.
• The recognition that light and matter have characteristics that are both wave-like and particle-like.

Special relativity

In 1905, Albert Einstein developed the theory of special relativity. However, the idea of relativity did not begin with him, as Galileo and Newton had been exploring relativity for centuries. The concept of relativity expresses the realisation that the laws of physics depend on the observer.

For example, if you fly into space at nearly the speed of light, time runs more slowly on your spacecraft than it does on the earth. So when you return to the earth, you will find that your friends have grown older than you have.

It is possible to divide modern relativity into two theories, special relativity and general relativity. The theory of special relativity is important because:

• It states that the laws of physics are the same and can be stated in their simplest form in all inertial frames of reference.
• It states that the speed of light (c ) is constant and independent of the relative motion of the source.
• An outcome of this theory is the famous equation: E = mc².

Einstein is well-known because his theories of relativity made ground-breaking predictions that came to fruition in the real world. Most significantly, his hypotheses have been proven to have been highly precise in a wide range of experiments, forever transforming our understanding of space and time.

Albert Einstein

How did turning points in physics influence science?

Turning points in physics have provided fundamental knowledge that has led to further discoveries and influenced technology in many ways. Examples include:

• The discovery of the electron, which brought in a new era in physical science, thus paving the way for modern ideas of atomic structure and chemistry.

• Wave-particle duality, which highlighted the inability of classical terms such as particle and wave to explain quantum-scale object behaviour.

• Special relativity theory, which has had a significant influence on physics, particularly in the computation and comprehension of high-velocity events. As a result, we now have a far better grasp of space and time than we did at the start of the century.

Turning Points in Physics - Key takeaways

• A turning point in physics is when a scientist made a revolutionary discovery or development that affected all subsequent understanding.
• Three main turning points in physics were the discovery of the electron, wave-particle duality, and special relativity.
• The discovery of the electron disproved the idea of a homogeneous and indivisible atom by discovering subatomic particles.
• Wave-particle duality helped develop the model of the atom by recognising that an electron possesses particle and wave-like properties.
• Special relativity has had a big impact on the calculation and understanding of high-velocity phenomena as well as on our understanding of space and time.

A turning point in physics is when a scientist makes a new discovery or development that has such an impact on physics that many previously held beliefs are now considered incorrect or questionable.

The three main turning points in physics are the discovery of the electron, wave-particle duality, and special relativity.

The turning points in physics are important because they formed the fundamentals of physics and opened new ways of understanding for many later discoveries to come.

Final Turning Points in Physics Quiz

Question

Who discovered the electron?

J. J. Thomson.

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When was the electron discovered?

In 1897.

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Were cathode ray tubes used in the discovery of the electron?

Yes, they were.

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What was the first subatomic particle that was discovered?

Electron.

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Did the discovery of the electron disprove the idea of an indivisible atom?

Yes, it did.

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Who proposed the theory of special relativity?

Albert Einstein.

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When was the theory of special relativity developed?

In 1905.

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Which famous equation was provided by special relativity?

E = mc².

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Who proposed wave-particle duality?

Louis de Broglie.

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When was wave-particle duality proposed?

In 1923.

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Which scientists studied wave-particle duality?

Max Planck, Albert Einstein, Louis de Broglie, Erwin Schrödinger, Niels Bohr, and Arthur Compton.

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What are the two parts of modern relativity?

The theory of special relativity and the theory of general relativity.

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What disproved the idea of a homogenous atom particle?

The discovery of the electron.

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Do light and matter have characteristics that are both wave-like and particle-like?

Yes, they do.

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Can you name the symbol for the speed of light?

It is c.

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Who discovered the granularity of electricity?

J. J. Thomson.

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Who was exploring relativity centuries before Einstein?

Galileo and Newton.

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Which of these discoveries was the most important one for our understanding of space and time?

Special relativity.

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Did wave-particle duality help to develop the model of the atom?

Yes, it did.

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According to Einstein, is time relative?

Yes, it is.

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Did the plum pudding model say atoms have a neutral total charge?

Yes, it did.

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Were cathode-ray tubes used in Thomson's experiment?

Yes

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What is the concept of the plum pudding model?

Negative particles are floating around in a positively charged soup in an atom.

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Who did the gold foil experiment?

Ernest Rutherford.

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When did the gold foil experiment take place?

In 1909.

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What was the big discovery of the gold foil experiment?

The nucleus

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Does the nucleus contain the bulk of the atomic mass?

Yes, it does.

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Who did the oil drop experiment?

Robert Millikan.

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Were electrons the first subatomic particles that were discovered?

Yes, they were.

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Was Thomson able to determine the charge of the electron in relation to its mass?

Yes.

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What else did Thomson study?

Positively charged particles in neon gas.

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In the plum pudding model, what were the raisins representing?

Electrons

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In the plum pudding model, what was the dough representing?

Positive charge

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What was Rutherford looking for in his experiment?

Alpha particles with high deflection angles.

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When did the Millikan oil-drop experiment take place?

In 1909.

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What was the big discovery of the oil-drop experiment?

First precise direct measurement of a single electron's charge.

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Can the charge on a drop be calculated using the balance of gravity and electric forces?

Yes, it can.

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The charge of an electron discovered may be quantised in units of what?

1.602176634 × 10 ^−19 coulomb.

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Which of the following is not one of the three big steps that helped understand electrons better?

Michelson-Morley experiment

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Who proposed the theory of special relativity?

Albert Einstein.

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When was the theory of special relativity conceived?

In 1905.

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What is Einstein's first postulate regarding the theory of special relativity about?

Reference frames.

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What is Einstein's second postulate regarding the theory of special relativity about?

The speed of light.

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In which context are all laws of physics the same to any observer?

In an inertial frame of reference.

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The speed of light in a vacuum is constant. Is the speed of light in matter lower or higher?

It is lower than c.

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What is the speed of light (c) in a vacuum?

It is 3.00 * 10 ^ 8 m / s.

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What was the aim of the Michelson-Morley experiment?

Comparing the speed of light in different directions to detect the relative motion.

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Which famous equation was provided by the theory of special relativity?

E = mc ^ 2.

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Which year was the Michelson-Morley experiment conducted?

1887.

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In which circumstances is length contraction possible?

In relativistic speeds.

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