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Faraday’s Law

Faraday’s Law. EMF= - DF B / D t. Transformer. The output emf of a transformer may be greater or smaller than its input emf A transformer operates on ac . E 1 =N 1 Df / D t E 2 =N 2 Df / D t E 1 /E 2 =N 1 /N 2 E 1 I 1 =E 2 I 2 (power input=power output)

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Faraday’s Law

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  1. Faraday’s Law EMF= - DFB/Dt

  2. Transformer • The output emf of a transformer may be greater or smaller than its input emf • A transformer operates on ac

  3. E1=N1Df/Dt E2=N2Df/Dt E1/E2=N1/N2 E1I1=E2I2 (power input=power output) So I1/I2=E2/E1=N2/N1

  4. Chapter 21 Electromagnetic Waves

  5. Physical Nature of EM Waves A changing magnetic field produces a changing electric field (Faraday’s law) DB/Dt E A changing electric field produces a changing magnetic field (Maxwell’s hypothesis) DE/Dt B

  6. Source of Electromagnetic Waves Electric field c • • • • • × × × × c Antenna c c=E/B Magnetic field EM waves are produced, fundamentally, by accelerating electric charges

  7. Types of Electromagnetic Waves

  8. Frequencyfand Wavelengthl f l=c or f=c/l Wavelength of visible light: 400 nm (Blue) to 750 nm (Red) (1 nm=10-9 m) Or 4000 Å to 7500 Å (1 Å=10-10 m)

  9. Question: In a vacuum, the speed of an electromagnetic wave • depends on its frequency • depends on its wavelength • depends on its electric and magnetic fields • is a universal constant Answer: d

  10. Which one of the following statements concerning electromagnetic waves is false? (a) Electromagnetic waves are longitudinal waves. (b) Electromagnetic waves transfer energy through space. (c) The existence of electromagnetic waves was predicted by Maxwell. (d) Electromagnetic waves can propagate through a material substance. (e) Electromagnetic waves do not require a physical medium X

  11. Which one of the following will notgenerate electromagnetic waves or pulses? (a) a steady direct current (b) an accelerating electron (c) a proton in simple harmonic motion (d) an alternating current (e) charged particles traveling in a circular path in a mass spectrometer X

  12. Complete the following sentence: When electrons from a heated filament accelerate through vacuum toward a positive plate, (a) only an electric field will be produced. (b) only a magnetic field will be produced. (c) electromagnetic waves will be produced. (d) longitudinal waves will be produced. (e) neither electric nor magnetic fields will be produced. X

  13. Which one of the following types of wave is intrinsically different from the other four? • radio waves • gamma rays • visible light • sound waves • ultraviolet radiation X

  14. Which one of the following statements concerning electromagnetic waves is false? (a) Electromagnetic waves carry energy. (b) X-rays have longer wavelengths than radio waves. (c) In vacuum, all electromagnetic waves travel at the same speed. (d) Lower frequency electromagnetic waves can be produced by oscillating circuits. (e) They consist of mutually perpendicular electric and magnetic fields that oscillate perpendicular to the direction of propagation. X

  15. Which one of the following statements concerning the wavelength of an electromagnetic wave in a vacuum is true? (a) The wavelength is independent of the speed of the wave for a fixed frequency. (b) The wavelength is inversely proportional to the speed of the wave. (c) The wavelength is the same for all types of electromagnetic waves. (d) The wavelength is directly proportional to the frequency of the wave. (e) The wavelength is inversely proportional to the frequency of the wave. X

  16. Complete the following sentence: The various colors of visible light differ in • frequency only. • frequency and wavelength. • (c) wavelength only. • (d) frequency and their speed in a vacuum. • (e) their speeds in a vacuum. X

  17. A cellular telephone transmits electromagnetic waves at a frequency of 935 MHz. What is the wavelength of these waves? (a) 0.0106 m (c) 0.642 m (e) 2.40 m (b) 0.321 m(d) 1.22 m X

  18. An average distance between the surface of the earth and the surface of the sun is 1.49x1011 m. How much time, in minutes, does it take for light leaving the surface of the sun to reach the earth? (a) zero minutes (c) 8.3 min(e) 500 min (b) 2.9x10–3 min (d) 74 min X

  19. Note the different types of electromagnetic radiation: (1) X-rays (4) visible light (2) radio waves (5) infrared radiation (3) gamma rays (6) ultraviolet radiation Which list correctly ranks the electromagnetic waves in order of increasing frequency? (a) 2, 3, 4, 5, 6, 1 (c) 2, 5, 4, 6, 1, 3(e) 3, 6, 1, 4, 5, 2 (b) 2, 5, 4, 1, 6, 3 (d) 3, 1, 6, 4, 5, 2 X

  20. X Which one of the following colors of visible light has the highest frequency? (a) Yellow (c) green (e) violet (b) Red (d) blue X

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