Chapter 31

© 2012 Pearson Education, Inc.

{{Chapter 31Chapter 31

Alternating Current Circuits (cont.)Alternating Current Circuits (cont.)


Transformers Transformers

• Power is supplied to the Power is supplied to the primaryprimary and delivered and delivered from the from the secondarysecondary. See . See Figure 31.21 at the right.Figure 31.21 at the right.

• Magnetic flux is confined Magnetic flux is confined to the iron core.to the iron core.

• Terminal voltages: Terminal voltages: VV22//VV11 = = NN22//NN11..

• Currents in primary and Currents in primary and secondary: secondary: VV11II11 = = VV22II22..


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


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






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






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






{{Chapter 32Chapter 32

Electromagnetic WavesElectromagnetic Waves


Maxwell’s equations and electromagnetic Maxwell’s equations and electromagnetic waveswaves Maxwell’s equations predict that an oscillating Maxwell’s equations predict that an oscillating

charge emits charge emits electromagnetic radiationelectromagnetic radiation in the in the form of electromagnetic waves.form of electromagnetic waves.

Figure 32.3 below shows the electric field lines Figure 32.3 below shows the electric field lines of a point charge undergoing simple harmonic of a point charge undergoing simple harmonic motion.motion.


The electromagnetic spectrum The electromagnetic spectrum

• The The electromagnetic spectrumelectromagnetic spectrum includes includes electromagnetic waves of all frequencies electromagnetic waves of all frequencies and wavelengths. (See Figure 32.4 below.)and wavelengths. (See Figure 32.4 below.)


Visible lightVisible light• Visible lightVisible light is the segment of the electromagnetic is the segment of the electromagnetic

spectrum that we can see. spectrum that we can see. • Visible light extends from the violet end (400 nm) to the Visible light extends from the violet end (400 nm) to the

red end (700 nm), as shown in Table 32.1.red end (700 nm), as shown in Table 32.1.• Eyes have three kinds of “cones” (cells sensitive to light)Eyes have three kinds of “cones” (cells sensitive to light)

• S : ~ 400 – 500 nmS : ~ 400 – 500 nm• M : ~ 450 – 600 nmM : ~ 450 – 600 nm• L : ~ 500 – 650 nmL : ~ 500 – 650 nm


Plane electromagnetic wavesPlane electromagnetic waves

• A A plane waveplane wave has a planar wave has a planar wave front. See Figure 32.5 below.front. See Figure 32.5 below.


A simple plane electromagnetic waveA simple plane electromagnetic wave

• The Plane wave The Plane wave satisfies Maxwell’s satisfies Maxwell’s equations.equations.

• Gauss’s Law is Gauss’s Law is illustrated belowillustrated below

• Faraday/Ampere’s Faraday/Ampere’s Laws to the right.Laws to the right.


Key properties of electromagnetic wavesKey properties of electromagnetic waves

• The magnitudes of the The magnitudes of the fields in vacuum are fields in vacuum are related by related by E = cB.E = cB.

• The speed of the The speed of the waves is waves is cc = 3.00 = 3.00 ×× 10108 8 m/s in vacuum.m/s in vacuum.

• The waves are The waves are transverse. transverse. Both fields Both fields are perpendicular to are perpendicular to the direction of the direction of propagation and to propagation and to each other. (See each other. (See Figure 32.9 at the Figure 32.9 at the right.)right.)


Fields of a sinusoidal waveFields of a sinusoidal wave

• Figure 32.13 Figure 32.13 (right) shows the (right) shows the electric and electric and magnetic fields magnetic fields for a sinusoidal for a sinusoidal wave along the wave along the xx--axis.axis.


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


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.



Sinusoidal electromagnetic wavesSinusoidal electromagnetic waves

• Waves passing Waves passing through a small through a small area far from a area far from a source can be source can be treated as treated as plane waves. plane waves. (See Figure (See Figure 32.12 at the 32.12 at the right.)right.)


Q32.2

A. positive x-direction.

B. negative x-direction.

C. positive y-direction.

D. negative y-direction.


At a certain point in space, the electric and magnetic fields of an electromagnetic wave at a certain instant are given by

3

5

ˆ 6 10 V/m

ˆ 2 10 T

E i

B k

This wave is propagating in the


A32.2

At a certain point in space, the electric and magnetic fields of an electromagnetic wave at a certain instant are given by

3

5

ˆ 6 10 V/m

ˆ 2 10 T

E i

B k

This wave is propagating in the

A. positive x-direction.

B. negative x-direction.





Q32.3

A. positive y-direction.

B. negative y-direction.

C. positive z-direction.

D. negative z-direction.


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


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.



In a sinusoidal electromagnetic wave in a vacuum, the electric field has only an x-component. This component is given by

Ex = Emax cos (ky + t)

This wave propagates in the

Q32.4

A. positive z-direction.

B. negative z-direction.





In a sinusoidal electromagnetic wave in a vacuum, the electric field has only an x-component. This component is given by

Ex = Emax cos (ky + t)

This wave propagates in the

A32.4

A. positive z-direction.

B. negative z-direction.




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Chapter 31