EMF Induced in Moving Conductor. Faraday s Law. Motional EMF=ΔΦ

Transcription

1 EMF Indued in Moving Condutor Faraday s Law Motional EMF=ΔΦ B /Δt=BΔA/ A/Δt=BlvΔt/ t/δt=blv EMF= - ΔΦ B /Δt

2 Chapter 21 Eletri Generator Alternating Current Transformer Eletromagneti Waves Έ=NBAωsinωt h N l S N S Loop horizontal EMF=max Loop vertial EMF=0 Transformer The output emf of a transformer may be greater or smaller than its input emf A transformer operates on a EMF E max -E max E=BlvsinΘ => E=2NBlvsinΘ=NBAω sinωt where Θ=ωt, v=ωr=ωh/2 t E 1 =N 1 Δφ/Δt E 2 =N 2 Δφ/Δt E 1 /E 2 =N 1 /N 2 E 1 I 1 =E 2 I 2 (power input=power output) So I 1 /I 2 =E 2 /E 1 =N 2 /N 1 Eletrial Power Transmission When transmitting eletri power over long distanes, it is most eonomial to use high voltage and low urrent Minimizes I 2 R power losses In pratie, voltage is stepped up to about V at the generating station and stepped down to V at the distribution station and finally to 120 V at the ustomer s utility pole

3 Question: Alternating urrent in the seondary oil of a transformer is indued by (a) a varying eletri field (b) a varying magneti field () the iron ore of the transformer (d) motion of the primary Answer: b Physial Nature of EM Waves A hanging magneti field produes a hanging eletri field (Faraday s law) ΔB/Δt A hanging eletri field produes a hanging magneti field (Maxwell s hypothesis) ΔE/Δt E B Soure of Eletromagneti Waves Types of Eletromagneti Waves Antenna Eletri field =E/B Magneti field EM waves are produed, fundamentally, by aelerating eletri harges Frequeny f and Wavelength λ f λ= or f=/λ 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) Question: In a vauum, the speed of an eletromagneti wave (a) depends on its frequeny (b) depends on its wavelength () depends on its eletri and magneti fields (d) is a universal onstant Answer: d

4 Whih one of the following statements onerning eletromagneti waves is false? X (a) Eletromagneti waves are longitudinal waves. (b) Eletromagneti waves transfer energy through spae. () The existene of eletromagneti waves was predited by Maxwell. (d) Eletromagneti waves an propagate through a material substane. (e) Eletromagneti waves do not require a physial medium Whih one of the following will not generate eletromagneti waves or pulses? X (a) a steady diret urrent (b) an aelerating eletron () a proton in simple harmoni motion (d) an alternating urrent (e) harged partiles traveling in a irular path in a mass spetrometer Complete the following sentene: When eletrons from a heated filament aelerate through vauum toward a positive plate, (a) only an eletri field will be produed. (b) only a magneti field will be produed. X () eletromagneti waves will be produed. (d) longitudinal waves will be produed. (e) neither eletri nor magneti fields will be produed. X Whih one of the following types of wave is intrinsially different from the other four? (a) radio waves (b) gamma rays () visible light (d) sound waves (e) ultraviolet radiation Whih one of the following statements onerning eletromagneti waves is false? (a) Eletromagneti waves arry energy. X(b) X-rays have longer wavelengths than radio waves. () In vauum, all eletromagneti waves travel at the same speed. (d) Lower frequeny eletromagneti waves an be produed by osillating iruits. (e) They onsist of mutually perpendiular eletri and magneti fields that osillate perpendiular to the diretion of propagation. Whih one of the following statements onerning the wavelength of an eletromagneti wave in a vauum is true? (a) The wavelength is independent of the speed of the wave for a fixed frequeny. (b) The wavelength is inversely proportional to the speed of the wave. () The wavelength is the same for all types of eletromagneti waves. (d) The wavelength is diretly proportional to the frequeny of the wave. X(e) The wavelength is inversely proportional to the frequeny of the wave.

5 Complete the following sentene: The various olors of visible light differ in (a) frequeny only. (b) frequeny and wavelength. X () wavelength only. (d) frequeny and their speed in a vauum. (e) their speeds in a vauum. A ellular telephone transmits eletromagneti waves at a frequeny of 935 MHz. What is the wavelength of these waves? (a) m () m (e) 2.40 m (b) m X (d) 1.22 m An average distane between the surfae of the earth and the surfae of the sun is 1.49x10 11 m. How muh time, in minutes, does it take for light leaving the surfae of the sun to reah the earth? (a) zero minutes () 8.3 min X (e) 500 min (b) 2.9x10 3 min (d) 74 min Note the different types of eletromagneti radiation: (1) X-rays (4) visible light (2) radio waves (5) infrared radiation (3) gamma rays (6) ultraviolet radiation Whih list orretly ranks the eletromagneti waves in order of inreasing frequeny? (a) 2, 3, 4, 5, 6, 1 () 2, 5, 4, 6, 1, 3 X (e) 3, 6, 1, 4, 5, 2 (b) 2, 5, 4, 1, 6, 3 (d) 3, 1, 6, 4, 5, 2 X Whih one of the following olors of visible light has the highest frequeny? (a) Yellow () green (e) violetx (b) Red (d) blue