physics

John Henry Poynting

John Henry Poynting is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand John Henry Poynting rather than just read about it. In short: John Henry Poynting FRS (9 September 1852 – 30 March 1914) was an English physicist. He was the first professor of physics at Mason Science College from 1880 to 1900, and then the successor institution, the University of Birmingham until his death.

Key takeaways

John Henry Poynting belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect John Henry Poynting to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of John Henry Poynting from memory before moving on to harder problems.

Reference excerpt

John Henry Poynting FRS (9 September 1852 – 30 March 1914) was an English physicist. He was the first professor of physics at Mason Science College from 1880 to 1900, and then the successor institution, the University of Birmingham until his death.

Early life and education Poynting was the youngest son of Thomas Elford Poynting, a Unitarian minister. He was born at the parsonage of the Monton Unitarian Chapel in Eccles, Lancashire, where his father served as minister from 1846 to 1878. In his boyhood, he was educated at the nearby school operated by his father. From 1867 to 1872, he attended Owens College, now the University of Manchester, where his physics teachers included Osborne Reynolds and Balfour Stewart. From 1872 to 1876 he was a student at the University of Cambridge, where he attained high honours in mathematics after taking grinds with Edward Routh.

Career In the late 1870s, he worked in the Cavendish Laboratory at Cambridge under James Clerk Maxwell. In 1880, he became the first professor of physics at the University of Birmingham. He was the developer and eponym of the Poynting vector, which describes the direction and magnitude of electromagnetic energy flow and is used in the Poynting theorem, a statement about energy conservation for electric and magnetic fields. This work was first published in 1884. He performed a measurement of Newton's gravitational constant by innovative means during 1893. In 1903 he was the first to realise that the Sun's radiation can draw in small particles towards it: this was later named the Poynting–Robertson effect. He discovered the torsion-extension coupling in finite strain elasticity. This is now known as the (positive) Poynting effect in torsion. Poynting and the Nobel prizewinner J. J. Thomson co-authored a multi-volume undergraduate physics textbook, which was in print for about 50 years and was in widespread use during the first third of the 20th century. Poynting wrote most of it. He was awarded an honorary MSc in Pure Science in 1901 by Birmingham University. Poynting lived at 11 St Augustine's Road, Edgbaston with his family and servants for some years. He previously lived at 66 Beaufort Road, Edgbaston (demolished) and died of a diabetic coma, aged 61, at 10 Ampton Road, Edgbaston in 1914. In 1880, he married Maria Adney Cropper. He was survived by his widow, a son, and two daughters.

Legacy Alfred J. Lotka was among Poynting's most famous students, being inspired by Poynting to apply the ideas of physical chemistry to biology. Lotka dedicated his classic book on mathematical population biology to Poynting. Poynting predicted the 'Poynting-Robertson effect', whereby a particle of dust orbiting a star experiences a drag force which makes it spiral slowly into the star. Howard P. Robertson later restated the prediction using general relativity. Poynting also founded and is the namesake of the popular student society at the University of Birmingham, 'The Poynting Physical Society' or PPS.

Craters on Mars and the Moon are named in his honour, as is the main physics building at the University of Birmingham and the departmental society there, the Poynting Physical Society. He is credited with coining the expression "greenhouse effect" in 1909 to explain how infrared-absorbing trace gasses such as carbon dioxide in the atmosphere increases the surface temperature of Earth and Mars.

Works by J. H. Poynting

1884 A Comparison of the Fluctuations in the Price of Wheat and in the Cotton and Silk Imports into Great Britain, Journal of the Royal Statistical Society; 47, 1884, pp. 34–64 1894 The Mean Density of the Earth London, C. Griffin 1899 (with J. J. Thomson) A Text-Book of Physics: volume I: Sound London, C. Griffin; 2nd edition, 1900 1902 (with J. J. Thomson) A Text-Book of Physics: volume II: Properties of Matter London, C. Griffin 1904 (with J. J. Thomson) A Text-Book of Physics: volume III: Heat London, C. Griffin 1913 The earth; its shape, size, weight and spin Cambridge University Press 1914 (with J. J. Thomson) A Text-Book of Physics: volume IV: Electricity and Magnetism. Pts. I and II: Static electricity and magnetism London, C. Griffin 1920 Collected Scientific Papers Cambridge University Press

References

External links Works by or about John Henry Poynting at Wikisource Quotations related to John Henry Poynting at Wikiquote Media related to John Henry Poynting at Wikimedia Commons

Illustrations

Worked examples

Example 1 — a first encounter with John Henry Poynting

Start with the simplest possible case. Write down what John Henry Poynting claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to John Henry Poynting before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about John Henry Poynting ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of John Henry Poynting

In research: John Henry Poynting appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses John Henry Poynting in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: John Henry Poynting is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1852 births, 1914 deaths, British fellows of the Royal Society, so understanding it makes those chapters shorter.
In everyday life: Look for John Henry Poynting outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study John Henry Poynting in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what John Henry Poynting means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain John Henry Poynting out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is John Henry Poynting in simple terms?

Why does John Henry Poynting matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study John Henry Poynting?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on John Henry Poynting.