https://www.boundless.com/physics/textbooks/boundless-physics-textbook/induction-ac-circuits-and-electrical-technologies-22/magnetic-fields-and-maxwell-revisited-164/maxwell-s-predictions-and-hertz-confirmation-591-6358/
Maxwell's prediction of the electromagnetic force was confirmed by Hertz who generated and detected electromagnetic waves.
Learning Objectives[ edit ]
- Explain how Maxwell's prediction of the electromagnetic force was confirmed by Hertz
- Identify predictions derived from the Maxwell's equations
Key Points[ edit ]
- Maxwell predicted that electric and magnetic forces are linked.
- Maxwell's equations predict that all light waves have the same structure, regardless of wavelength and frequency.
- Hertz was able to confirm Maxwell's equation experimentally by generating and detecting certain types of electromagnetic waves in the laboratory.
Terms[ edit ]
- electromotive force (EMF)—The voltage generated by a battery or by the magnetic force according to Faraday's Law. It is measured in units of volts, not newtons, and thus, is not actually a force.
- magnetic field A condition in the space around a magnet or electric current in which there is a detectable magnetic force, and where two magnetic poles are present.
- electric field A region of space around a charged particle, or between two voltages; it exerts a force on charged objects in its vicinity.
Full Text[ edit ]
Maxwell's Predictions and Hertz' Confirmation
Combining the work of physicists including Oersted, Coulomb, Gauss, and Faraday, and adding his own insights, James Clerk Maxwell developed a complete and overarching theory showing electric and magnetic forces are not separate, but different forms of the same thing: the electromagnetic force. In 1865, he did this in the form of four equations that state the following:- Electric field lines originate on positive charges and terminate on negative charges, and the electric field is defined as the force per unit charge on a test charge. The strength of the force is related to the electric constant ε0, also known as the permitivity of free space.
- Magnetic field lines are continuous, having no beginning or end. No magnetic monopoles are known to exist.
- A changing magnetic field induces an electromotive force (emf) and, hence, an electric field. The direction of the emf opposes the change.
- Magnetic fields are generated by moving charges or by changing electric fields .
Proving Maxwell's Equations
Simple and brilliant in their insight, Maxwell's famous equations would still be hard to prove. Since changing electric fields create relatively weak magnetic fields, they could not be easily detected at the time of Maxwell's hypothesis.It was not until 1888 that Maxwell's prediction passed an important test when Heinrich Hertz generated and detected certain types of electromagnetic waves in the laboratory. He performed a series of experiments that not only confirmed the existence of electromagnetic waves, but also verified that they travel at the speed of light.
Hertz used an AC RLC (resistor-inductor-capacitor) circuit that resonates at a known frequency and connected it to a loop of wire as shown in . High voltages induced across the gap in the loop produced sparks that were visible evidence of the current in the circuit and that helped generate electromagnetic waves. Across the laboratory, Hertz had another loop attached to another RLC circuit, which could be tuned (as the dial on a radio) to the same resonant frequency as the first and could, thus, be made to receive electromagnetic waves. This loop also had a gap across which sparks were generated, giving solid evidence that electromagnetic waves had been received.
Apparatus Used by Hertz
The apparatus used by Hertz in 1887 to generate and detect electromagnetic waves. An RLC circuit connected to the first loop caused sparks across a gap in the wire loop and generated electromagnetic waves. Sparks across a gap in the second loop located across the laboratory gave evidence that the waves had been received.
EM Wave
The propogation of an electromagnetic wave as predicted by Maxwell and confirmed by Hertz.
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Source: Boundless. “Maxwell's Predictions and Hertz' Confirmation.” Boundless Physics. Boundless, 21 Jul. 2015. Retrieved 02 Jan. 2016 from https://www.boundless.com/physics/textbooks/boundless-physics-textbook/induction-ac-circuits-and-electrical-technologies-22/magnetic-fields-and-maxwell-revisited-164/maxwell-s-predictions-and-hertz-confirmation-591-6358/
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