Download presentation

Presentation is loading. Please wait.

Published byLorena Ailey Modified over 2 years ago

1
Alternating Current Circuits And Electromagnetic Waves Chapter 21

2
Introduction Alternating current circuits play an important part in our lives. –Electrical power production and transmission –Communication systems –Entertainment –Medicine 224, 229

3
We will study –Circuits containing a source of emf and one or more of the following in series: Resistors Capacitors Inductors

4
We will study –Electromagnetic waves Composed of fluctuating electrical and magnetic waves –Radio frequencies (RF) –Radar –Microwaves –Infrared –Visible light –Ultraviolet –X-rays –Gamma Rays

6
AC Generators The output of an ac generator –ac generator symbol –Formula for instantaneous voltage ( v) 21.1/21.2

7
Resistors In An ac Circuit Current and voltage are in step with each other. (in phase)

8
The average value of the current over one cycle is zero. Power formula:

9
rms Current rms current (root mean square) –It is the direct current that would dissipate the same amount of energy in a resistor as an ac current of that value.

10
Rms Voltage Rms voltage –120 V rms in our homes

11
Ohm’s Law In An ac Circuit Ohm’s Law is valid for resistors in ac circuits.

12
Review Capacitors in a dc circuit –Charging As the voltage across the capacitor increases, the current decreases. –RC time constant 21.4

13
Capacitors In An ac Circuit In a capacitive ac circuit, the current always leads the voltage by 90 o. 21.5

14
Capacitive Reactance Capacitive reactance (ohms) –Similar to resistance in a dc circuit Decreases with frequency –Opposes a change in ac voltage –Formulas:

15
Inductive Reactance Inductive reactance (ohms) –Similar to resistance in a dc circuit Increases with frequency –Opposes a change in ac current –Formulas: 21.6/21.7

16
In an inductive ac circuit, the voltage always leads the current by 90 o. ELI the ICE man 21.7

17
ELI the ICE man Three important relationships: –The instantaneous voltage across the resistor is in phase with the instantaneous current. –The instantaneous voltage across the inductor leads the instantaneous current by 90 o. –The instantaneous voltage across the capacitor lags the instantaneous current by 90 o.

18
The RLC Series Circuit Impedance (Z) –The total resistance (ohms) in an ac circuit –Formula: 221

19
Phasors –Rotating vectors which are used to represent the voltage across each component. Separated by 90 o –Phase angle 222

20
Phase Angle Phase angle

21
Schematic Symbols Review of circuit symbols –Table 21.2 (pg. 705) –Electronic Symbol Handout 23

22
Power In An ac Circuit No power is lost in capacitors or in pure inductors. –A capacitor in an ac circuit does not dissipate energy. –A pure inductor in a ac circuit does not dissipate energy.

23
Power Formulas: NOTE: cos is called the power factor

24
Review Mechanical Resonance 91, 95

25
Resonance In A Series RLC Circuit Resonant frequency (f o ) The frequency at which X L = X C Important in tuning circuits Radios, televisions, cell phones Airport metal detectors Formula: 223

26
QUESTIONS 1 - 4, 6, 7 Pg. 726

27
Transformers What is a transformer? 218

28
Transformer Voltage A transformer steps up or steps down ac voltages Primary and secondary coils 218

29
Transformer Power The power input to the primary equals the power output at the secondary.

30
Transformer Efficiency Efficiencies are between 90% and 99%.

31
The Transformer Equation N p /N s is the turns ratio

32
The Transformer Applications: AC/DC electronic equipment Power distribution Automobile ignition systems 219, 220

33
Maxwell’s Theory Electric field lines originate on positive charges and terminate on negative charges. Magnetic field lines always form closed loops. A varying magnetic field induces an emf and hence an electric field. Magnetic fields are generated by moving charges (or currents). 21.18

34
Maxwell’s Hypothesis A changing electric field should produce a magnetic field. This could not be proven experimentally because the electric fields were too weak to detect at the time.

35
Maxwell’s Prediction Maxwell came up with the concept of electromagnetic waves and predicted that they would travel at the speed of light. 21.20

36
Maxwell’s Conclusion He concluded that light waves are electromagnetic in nature.

37
Hertz’s Discovery Hertz was the first to generate and detect electromagnetic waves in the laboratory. 21.17

38
Hertz’s Apparatus

39
EM Resonance Hertz achieved resonance and transferred electromagnetic energy between two coils which were several meters apart. Resonant frequency (f o ) formula

40
Properties EM Radiation Hertz showed that electromagnetic radiation exhibited wave properties. Reflection Refraction Diffraction Interference Polarization 231, 232

41
The Speed of EM Waves Hertz showed that electromagnetic radiation traveled at the speed of light.

42
Hertz’s Contribution Hertz’s experiments provided the first proof of Maxwell’s theories.

43
Production Of EM Waves By An Antenna Energy stored in an LC circuit is constantly transferred between the electric and magnetic fields. Electromagnetic waves are generated if this happens rapidly. Antennas are used to produce electromagnetic waves. 177, 178

44
EM Waves 228

45
Properties Of EM Waves Electromagnetic waves are transverse waves. They travel at the speed of light. Light is an electromagnetic wave They can travel through a vacuum.

46
A Special Relationship The ratio of the electric field strength (E) to the magnetic field strength (B) equals the speed of light.

47
Energy and Momentum Electromagnetic waves carry both energy and momentum.

48
The Speed of EM Waves Important formula:

49
Visible Light Range of wavelengths for visible light: 400 nm to 700 nm 69

50
The Spectrum Of EM Waves Types of waves (increasing in frequency and energy) Radio waves Microwaves Infrared waves (heat waves) Visible light Ultraviolet light (UV) X-rays Gamma rays 21.23

51
Review - The Doppler Effect Sound waves exhibit the Doppler effect Trains Race cars

52
The Doppler Effect For EM Waves Astronomy The expanding universe Red shift Blue shift Rotation of galaxies

53
The Red Shift

54
QUESTIONS 9 - 15 Pg. 726

Similar presentations

OK

Class 34 Today we will: learn about inductors and inductance

Class 34 Today we will: learn about inductors and inductance

© 2018 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Ppt on viruses and anti viruses cnet Ppt on eia report bakken Ppt on organic farming vs chemical farming Ppt on conservation of minerals Ppt on point contact diodes Ppt on scanner and its types Training ppt on email etiquettes Ppt on second law of thermodynamics entropy Ppt on internal auditing process flowchart Ppt on op amp circuits examples