physics

John Hopkinson

John Hopkinson 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 Hopkinson rather than just read about it. In short: John Hopkinson, FRS, (27 July 1849 – 27 August 1898) was a British physicist, electrical engineer, Fellow of the Royal Society and President of the IEE (now the IET) twice in 1890 and 1896. He invented the three-wire (three-phase) system for the distribution of electrical power, for which he was granted a patent in 1882.

Key takeaways

John Hopkinson 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 Hopkinson to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of John Hopkinson from memory before moving on to harder problems.

Reference excerpt

John Hopkinson, FRS, (27 July 1849 – 27 August 1898) was a British physicist, electrical engineer, Fellow of the Royal Society and President of the IEE (now the IET) twice in 1890 and 1896. He invented the three-wire (three-phase) system for the distribution of electrical power, for which he was granted a patent in 1882. He also worked in many areas of electromagnetism and electrostatics, and in 1890 was appointed professor of electrical engineering at King's College London, where he was also director of the Siemens Laboratory. Hopkinson's law, the magnetic counterpart to Ohm's law, is named after him.

Life and career John Hopkinson was born in Manchester, the eldest of 5 children. His father, also called John, was a mechanical engineer. He was educated at Queenwood School in Hampshire and Owens College in Manchester. He won a scholarship to Trinity College, Cambridge in 1867 and graduated in 1871 as Senior Wrangler, having placed first in the demanding Cambridge Mathematical Tripos examination. During this time he also studied for and passed the examination for a BSc from the University of London. Hopkinson could have followed a purely academic career but instead chose engineering as his vocation. He was a Cambridge Apostle. After working first in his father's engineering works, Hopkinson took a position in 1872 as an engineering manager in the lighthouse engineering department of Chance Brothers and Company in Smethwick. In 1877 Hopkinson was elected a Fellow of the Royal Society in recognition of his application of Maxwell's theory of electromagnetism to problems of electrostatic capacity and residual charge. In 1878 he moved to London to work as a consulting engineer, focusing particularly on developing his ideas about how to improve the design and efficiency of dynamos. Hopkinson's most important contribution was his three-wire distribution system, patented in 1882. In 1883 Hopkinson showed mathematically that it was possible to connect two alternating current dynamos in parallel-—a problem that had long bedevilled electrical engineers. He also studied magnetic permeability at high temperature, and discovered what was later called the Hopkinson peak effect. The series-parallel method of electric motor control, for which Hopkinson was granted a British patent in 1881, would prove to be an important advance in the development of electric railways. He applied for a US patent in 1892, triggering an interference proceeding against American inventor Rudolph M Hunter, who had been granted a US patent for the method in 1888. The US Patent Office affirmed Hopkinson's claim to priority of invention, but his British patent expired before the case was resolved, rendering him ineligible for a US patent (his US patent, had one been issued, would have expired concurrently with his British patent). Hopkinson twice held the office of President of the Institution of Electrical Engineers. During his second term, Hopkinson proposed that the Institution should make available the technical knowledge of electrical engineers for the defence of the country. In 1897 the Volunteer Corps of Electrical Engineers was formed and Hopkinson became major in command of the corps.

Personal life and legacy

Hopkinson was a member of the Alpine Club from 1889 until his death but he had been an active mountaineer in the alps for some years before that. He had made a number of significant alpine ascents with his brothers, Charles and Edward, his son Bertram and daughter Alice had joined him on some of those ascents. His climbing included some first ascents and new routes undertaken without guides, a summary of his alpine activities is given in Mumm's Alpine Register. On 27 August 1898, Hopkinson and three of his six children, John Gustave, Alice and Lina Evelyn, were killed in a mountaineering accident on the Petite Dent de Veisivi, Val d'Hérens, in the Pennine Alps, Switzerland. As a memorial to John Hopkinson and his son, the 1899 extension to the Engineering Laboratory at the New Museums Site as part of the University of Cambridge was named after him. A plaque commemorating this adorns the upper part of the wall in Free School Lane. The Hopkinson Professorship of Applied Thermodynamics (latterly and currently the Hopkinson and Imperial Chemical Industries Professorship of Applied Thermodynamics) was created in his memory. There is a sundial in the gardens of Newnham College, Cambridge memorialising Alice Hopkinson, from where she had recently graduated; the Lina Evelyn Hopkinson Scholarship is awarded to pupils at Wimbledon High School for excellence in English Literature. At the Victoria University of Manchester (now part of UMIST, which is now amalgamated with the University of Manchester) the Electro-technical Laboratory (1912) in Coupland Street, Manchester was named after him. His wife Evelyn (née Oldenburg), his two sons Bertram and Cecil (christened Rudolf), and his daughter Ellen (married James Alfred Ewing in 1912) are buried in the Ascension Parish Burial Ground, Cambridge; the rest of the family are buried at Cimetière de Territet (part of St John's English Church) at Territet, a municipality south of Montreux, Switzerland. Cecil (1891-1917) shared rooms with Lawrence Bragg whilst they were both studying at Trinity College, Cambridge and they became firm friends, he incurred a severe head wound in the 1914-19 war and died a few months after being invalided back to the UK. Bragg subsequently married Cecil's cousin Alice Hopkinson.

See also Electric motor Three-phase electric power Polyphase system Rigid collectors Bertram Hopkinson, his son Alfred Hopkinson and Edward Hopkinson, his younger brothers Austin Hopkinson, his nephew

References

Further reading Hopkinson, Mary & Ewing, Irene, Lady (eds.) (1948) John and Alice Hopkinson 1824-1910. London: Farmer & Sons, printers

External links

Works by or about John Hopkinson at the Internet Archive John Hopkinson John Hopkinson Biography

Illustrations

Worked examples

Example 1 — a first encounter with John Hopkinson

Start with the simplest possible case. Write down what John Hopkinson 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 Hopkinson 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 Hopkinson 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 Hopkinson

In research: John Hopkinson 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 Hopkinson 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 Hopkinson is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1849 births, 1898 deaths, 19th-century British engineers, so understanding it makes those chapters shorter.
In everyday life: Look for John Hopkinson 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 Hopkinson in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what John Hopkinson 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 Hopkinson out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is John Hopkinson in simple terms?

Why does John Hopkinson 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 Hopkinson?

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 Hopkinson.