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Nineteenth century produced a revolution in understanding of electricity and magnetism

Nineteenth century produced a revolution in understanding of electricity and magnetism Culminated in the work of James Maxwell. Electricity and magnetism were once thought to be unrelated, until Oersted and Ampère, Faraday and Henry.

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Nineteenth century produced a revolution in understanding of electricity and magnetism

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  1. Nineteenth century produced a revolution in understanding of electricity and magnetism • Culminated in the work of James Maxwell. • Electricity and magnetism were once thought to be unrelated, until Oersted and Ampère, Faraday and Henry. • Now we know that electricity and magnetism are so closely related, that when physicists list the forces of nature, electromagnetism is usually counted as just one. • Maxwell gathered everything together and expressed it in terms of four, famous equations.

  2. The universe according to Maxwell... • Write down the equation and list what the symbols mean, with units if you can. • Using information from your data sheet, calculate the speed of electromagnetic radiation in a vacuum.

  3. Wave Particle Duality: Maxwell and Hertz • Maxwell and suggested that light was one form of electromagnetic radiation. • The search for other forms of e/m radiation was on! In 1887 Heinrich Hertz discovered waves which had wavelengths of several metres compared to fractions of a mm.

  4. Heinrich Hertz Heinrich Rudolf Hertz (22 February 1857 – 1 January 1894) was a German physicist who clarified and expanded the electromagnetic theory of light that had been put forth by James Clerk Maxwell. He was the first to conclusively prove the existence of electromagnetic waves by engineering instruments to transmit and receive radio pulses using experimental procedures that ruled out all other known wireless phenomena. The scientific unit of frequency — cycles per second — was named the "hertz" in his honour.

  5. How did Hertz prove the existence of radio waves? Receiver Spark gap transmitter • The high frequency oscillations induce a voltage in the loop which was sufficient to cause a small spark to jump. • The spark could be made more powerful if the loop was put at the focal point of a concave mirror. • If he put the loop on its side, the effect was not seen at all, indicating that the waves were polarised. • Copy the diagram and use this to explain how Hertz proved the existence of radio waves: Key points • The induction coil produces a very high voltage. • The electric field strength between the spheres is strong enough for the insulating properties of air to break down (approximately 3000 V/mm). • When the spark jumps, it generates a spark that produces a high frequency damped electrical oscillation.

  6. Your tasks: • Define polarisation of a wave, and explain why Hertz’s experiment showed that the radio waves were polarised. • EXT: Why were the radio waves polarised? • Make a sketch of the diagram. Explain how by reflecting radio waves from a metal screen, Hertz could calculate the speed of the radio waves. Include equations

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