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© 2012 Pearson Education, Inc. { Chapter 31 Alternating Current Circuits (cont.)

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1 © 2012 Pearson Education, Inc. { Chapter 31 Alternating Current Circuits (cont.)

2 © 2012 Pearson Education, Inc. Transformers Power is supplied to the primary and delivered from the secondary. See Figure at the right. Power is supplied to the primary and delivered from the secondary. See Figure at the right. Magnetic flux is confined to the iron core. Magnetic flux is confined to the iron core. Terminal voltages: V 2 /V 1 = N 2 /N 1. Terminal voltages: V 2 /V 1 = N 2 /N 1. Currents in primary and secondary: V 1 I 1 = V 2 I 2. Currents in primary and secondary: V 1 I 1 = V 2 I 2.

3 © 2012 Pearson Education, Inc. In the transformer shown in the drawing, there are more turns in the secondary than in the primary. In this situation, the voltage amplitude is Q31.8 A. greater in the primary than in the secondary. B. smaller in the primary than in the secondary. C. the same in the primary and in the secondary. D. not enough information given to decide

4 © 2012 Pearson Education, Inc. In the transformer shown in the drawing, there are more turns in the secondary than in the primary. In this situation, the voltage amplitude is A31.8 A. greater in the primary than in the secondary. B. smaller in the primary than in the secondary. C. the same in the primary and in the secondary. D. not enough information given to decide

5 © 2012 Pearson Education, Inc. Q31.9 In the transformer shown in the drawing, there are more turns in the secondary than in the primary. In this situation, the current amplitude is A. greater in the primary than in the secondary. B. smaller in the primary than in the secondary. C. the same in the primary and in the secondary. D. not enough information given to decide

6 © 2012 Pearson Education, Inc. In the transformer shown in the drawing, there are more turns in the secondary than in the primary. In this situation, the current amplitude is A31.9 A. greater in the primary than in the secondary. B. smaller in the primary than in the secondary. C. the same in the primary and in the secondary. D. not enough information given to decide

7 © 2012 Pearson Education, Inc. { Chapter 32 Electromagnetic Waves

8 © 2012 Pearson Education, Inc. Maxwell’s equations and electromagnetic waves  Maxwell’s equations predict that an oscillating charge emits electromagnetic radiation in the form of electromagnetic waves.  Figure 32.3 below shows the electric field lines of a point charge undergoing simple harmonic motion.

9 © 2012 Pearson Education, Inc. The electromagnetic spectrum The electromagnetic spectrum includes electromagnetic waves of all frequencies and wavelengths. (See Figure 32.4 below.) The electromagnetic spectrum includes electromagnetic waves of all frequencies and wavelengths. (See Figure 32.4 below.)

10 © 2012 Pearson Education, Inc. Visible light Visible light is the segment of the electromagnetic spectrum that we can see. Visible light is the segment of the electromagnetic spectrum that we can see. Visible light extends from the violet end (400 nm) to the red end (700 nm), as shown in Table Visible light extends from the violet end (400 nm) to the red end (700 nm), as shown in Table Eyes have three kinds of “cones” (cells sensitive to light) Eyes have three kinds of “cones” (cells sensitive to light) S : ~ 400 – 500 nm S : ~ 400 – 500 nm M : ~ 450 – 600 nm M : ~ 450 – 600 nm L : ~ 500 – 650 nm L : ~ 500 – 650 nm

11 © 2012 Pearson Education, Inc. Plane electromagnetic waves A plane wave has a planar wave front. See Figure 32.5 below. A plane wave has a planar wave front. See Figure 32.5 below.

12 © 2012 Pearson Education, Inc. A simple plane electromagnetic wave The Plane wave satisfies Maxwell’s equations. The Plane wave satisfies Maxwell’s equations. Gauss’s Law is illustrated below Gauss’s Law is illustrated below Faraday/Ampere’s Laws to the right. Faraday/Ampere’s Laws to the right.

13 © 2012 Pearson Education, Inc. Key properties of electromagnetic waves The magnitudes of the fields in vacuum are related by E = cB. The magnitudes of the fields in vacuum are related by E = cB. The speed of the waves is c = 3.00 × 10 8 m/s in vacuum. The speed of the waves is c = 3.00 × 10 8 m/s in vacuum. The waves are transverse. Both fields are perpendicular to the direction of propagation and to each other. (See Figure 32.9 at the right.) The waves are transverse. Both fields are perpendicular to the direction of propagation and to each other. (See Figure 32.9 at the right.)

14 © 2012 Pearson Education, Inc. Fields of a sinusoidal wave Figure (right) shows the electric and magnetic fields for a sinusoidal wave along the x- axis. Figure (right) shows the electric and magnetic fields for a sinusoidal wave along the x- axis.

15 © 2012 Pearson Education, Inc. In a vacuum, red light has a wavelength of 700 nm and violet light has a wavelength of 400 nm. This means that in a vacuum, red light Q32.1 A. has higher frequency and moves faster than violet light. B. has higher frequency and moves slower than violet light. C. has lower frequency and moves faster than violet light. D. has lower frequency and moves slower than violet light. E. none of the above

16 © 2012 Pearson Education, Inc. In a vacuum, red light has a wavelength of 700 nm and violet light has a wavelength of 400 nm. This means that in a vacuum, red light A32.1 A. has higher frequency and moves faster than violet light. B. has higher frequency and moves slower than violet light. C. has lower frequency and moves faster than violet light. D. has lower frequency and moves slower than violet light. E. none of the above

17 © 2012 Pearson Education, Inc. Sinusoidal electromagnetic waves Waves passing through a small area far from a source can be treated as plane waves. (See Figure at the right.) Waves passing through a small area far from a source can be treated as plane waves. (See Figure at the right.)

18 © 2012 Pearson Education, Inc. Q32.2 A.positive x-direction. B.negative x-direction. C. positive y-direction. D. negative y-direction. E. none of the above At a certain point in space, the electric and magnetic fields of an electromagnetic wave at a certain instant are given by This wave is propagating in the

19 © 2012 Pearson Education, Inc. A32.2 At a certain point in space, the electric and magnetic fields of an electromagnetic wave at a certain instant are given by This wave is propagating in the A.positive x-direction. B.negative x-direction. C. positive y-direction. D. negative y-direction. E. none of the above

20 © 2012 Pearson Education, Inc. Q32.3 A.positive y-direction. B.negative y-direction. C. positive z-direction. D. negative z-direction. E. none of the above A sinusoidal electromagnetic wave in a vacuum is propagating in the positive z-direction. At a certain point in the wave at a certain instant in time, the electric field points in the negative x-direction. At the same point and at the same instant, the magnetic field points in the

21 © 2012 Pearson Education, Inc. A32.3 A sinusoidal electromagnetic wave in a vacuum is propagating in the positive z-direction. At a certain point in the wave at a certain instant in time, the electric field points in the negative x-direction. At the same point and at the same instant, the magnetic field points in the A.positive y-direction. B.negative y-direction. C. positive z-direction. D. negative z-direction. E. none of the above

22 © 2012 Pearson Education, Inc. In a sinusoidal electromagnetic wave in a vacuum, the electric field has only an x-component. This component is given by E x = E max cos (ky +  t) This wave propagates in the Q32.4 A. positive z-direction. B. negative z-direction. C. positive y-direction. D. negative y-direction. E. none of the above

23 © 2012 Pearson Education, Inc. In a sinusoidal electromagnetic wave in a vacuum, the electric field has only an x-component. This component is given by E x = E max cos (ky +  t) This wave propagates in the A32.4 A. positive z-direction. B. negative z-direction. C. positive y-direction. D. negative y-direction. E. none of the above


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