Maxwell’s complete theory shows that electric and magnetic forces are not separate, but different manifestations of the same thing-the electromagnetic force. Magnetic fields are generated by moving charges or by changing electric fields.The direction of the emf opposes the change, changing direction of the magnetic field. A changing magnetic field induces an electromotive force (emf) and, hence, an electric field.The strength of the magnetic force is related to the magnetic constant, μ 0. No magnetic monopoles are known to exist. Magnetic field lines are continuous, having no beginning or end. The electric field is defined as the force per unit charge on a test charge, and the strength of the force is related to the electric constant, ε 0. Electric field lines originate on positive charges and terminate on negative charges.However, the equations illustrate how apparently simple mathematical statements can elegantly unite and express a multitude of concepts-why mathematics is the language of science. Maxwell’s equations are paraphrased here in words because their mathematical content is beyond the level of this text. Maxwell brought together all the work that had been done by brilliant physicists, such as Ørsted, Coulomb, Ampere, Gauss, and Faraday, and added his own insights to develop the overarching theory of electromagnetism. Although he died young, Maxwell not only formulated a complete electromagnetic theory, represented by Maxwell’s equations, he also developed the kinetic theory of gases, and made significant contributions to the understanding of color vision and the nature of Saturn’s rings. The Scottish physicist James Clerk Maxwell (1831–1879) is regarded widely to have been the greatest theoretical physicist of the nineteenth century. With how many of these types are you familiar? Figure 15.3 shows the frequency and wavelength ranges of various types of EMR. Because frequency is inversely proportional to wavelength, any form of EMR can also be represented by its range of wavelengths. These forms are characterized by a range of frequencies. Amplitude: The height of the crest above the null pointĪs mentioned, electromagnetic radiation takes several forms.Frequency-The number of wave crests that pass a point per second, expressed in hertz (Hz or s –1).
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