- John Kerr (physicist)
Rev. John Kerr (
December 17, 1824– August 15, 1907) was a Scottish physicistwho inaugurated the field of electro-optics.
Ardrossanto a fish merchant, Kerr attended the University of Glasgowfrom where he earned a master's degree in divinity, subsequently being ordained a minister of the Free Church of Scotland. He also displayed an enthusiasm and ability in mathematicsand physicsand when his contemporary Lord Kelvinbecame professor of natural philosophyin 1846 the two became close friends, Kerr helping Kelvin to found the first physical laboratory at a British university.Steele (2004)]
In 1857, Kerr became lecturer in mathematics and physical science at the
Free Church Training Collegein Glasgow. It was there, in 1875, that he discovered the Kerr electro-optic effect. A strong electric potential, applied in a direction normal to a beam of light, causes a difference in refractive indexfor light polarised in the plane of the field and light polarised normal to it, an effect known as birefringence. This causes the resultant polarisationof the light to change.
The effect is exploited in the "Kerr cell" which is used in applications such as shutters in high-speed
photography, with shutter-speeds as fast as 100 ns. In 1928 Karolus & Mittelstaedt used a Kerr cell to modulate a beam of light in order to measure its speed. Earlier measurements had used mechanical means of modulationachieving frequencies of around 10 kHz while the Kerr cell allow frequencies of 10 MHz and greater precision of measurement. Kerr's original cell was a glassblock while modern cells are more commonly filled with liquids such as nitrobenzene.
Kerr Effect, the change in refractive indexis proportional to the square of the electric field. Where the relationship is linear, the effect is known as the Pockels effect. Kerr also demonstrated a similar effect for magnetic fields known as the magneto-optic Kerr effect. Light from lasers allows the achievement of the effect using the light's own electric field, the "AC Kerr effect".
Kerr was an early champion of the
metric systemin the UK.
LL.Dfrom the University of Glasgowin recognition of his contributions to physical science (1864);
*Fellow of the
Royal Medalof the Royal Society (1898);
Civil list pension(1902).
The Times", August 19, 1907, 12"c"
**"Nature", 76 (1907), 575–6----
*Green, G. & Lloyd, J.T. (1970) "Kelvin's instruments and the Kelvin Museum" "pp"55–6
*Kerr, K. (1863) "The Metric System"
*— (1867) "An Elementary Treatise on Rational Mechanics"
*Steele, R. rev. Anita McConnell (2004) " [http://www.oxforddnb.com/view/article/34300 Kerr, John (1824-1907)] ", "
Oxford Dictionary of National Biography", Oxford University Press, accessed 19 June 2005 ODNBsub
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