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Introduction to Electronics, 6th Ed, Eric Gates AC AC Measurements Resistive AC Circuits Capacitive AC Circuits Inductive AC Circuits Resonance Circuits

### Electromagnetic Induction

The process of inducing a voltage in a conductor by passing it through a magnetic field.

### Cycle

One revolution of an AC generator.

(Also, two complete alternations of voltage with NO reference to time.)

### Sine wave values (pair of numbers)

Degree of rotation- armature's position in the field.

Amplitude-value in relation to maximum or minimum.

### Peak value

Absolute value (no negative numbers) of the point of greatest magnitude. (The peak of the curve-positive or negative)

### Effective value

The amount that produces the same degree of heat in a given resistance as an equal amount of DC.

### Frequency

The number of cycles that occurs in a specific period of time.

(Usually cycles per second)

### Pulse width

(Square wave) The duration that the voltage is at the max or min amplitude. Pulse width is one half of the period-hence square.

### Triangular wave harmonics

Fundamental frequency and all ODD harmonics AND all are 180 degrees out of phase.

### How is AC current measured with a moving coil meter?

The AC current must first be converted to DC.

### Clamp on ammeter

A split core transformer. It is clamped around the conductor and uses the voltage induced by the conductors magnetic field

### Oscilloscope provides the following data:

Frequency

Duration

Phase relationship (of 2 or more waveforms)

Shape of a waveform

Amplitude

### Parts of an oscilloscope:

Cathode Ray Tube

Sweep generator

Horizontal deflection amp

Vertical deflection amp

Power supply

### In phase

Phase relationship such that current and voltage pass through peaks and zeros at the same time.

### Purely resistive circuits are

IN PHASE. Voltage and current pass through max and zero at the same point.

### Does current flow across a capacitor?

NO! The capacitor charging and discharging results in movement of electrons from one plate to the other. This resembles current flow.

### Capacitive Circuit Operation

Voltage starts from zero. Capacitor is empty. Current becomes max. Capacitor charges. Current drops as voltage becomes max and capacitor nears full charge. At max voltage capacitor is fully charged & current drops to zero. Voltage drops towards negative. Capacitor opposes and negative current flows as capacitor discharges.

### RC Low Pass Operation

Allows low frequencies to pass while attenuating high frequency. At low frequency, capacitive reactance is HIGH so voltage drop is across capacitor.

### RC High Pass Operation

Allows high frequency to pass while attenuating low.

At high frequency, capacitive reactance is LOW so voltage drop is across the resistor.

### Counter Electromotive Force (CEMF)

Voltage induced in an inductor coil which opposes the applied voltage. It is out of phase by 180 degrees.

### Factors effecting CEMF

The greater the rate of change of the magnetic field (faster the magnetic field expands or collapses) the greater the CEMF.

### RC Low pass filter - Memory Trick

Capacitor low = frequency low

(Capacitor low in schematic. Low frequency passes)

### RC High pass filter - Memory Trick

Capacitor high=frequency high

(Capacitor high in schematic. High frequency passes)

###
Leading Output Phase-Shift Network

Memory Trick

Look for C. (C slows voltage) C in back - input slow-output leads. Output voltage leads input voltage.

###
Lagging Output Phase-Shift Network

Memory Trick

Look for C. (C slows voltage) C in front-output slow-input leads. Output voltage lags input voltage.

### Why is the capacitive voltage vector (Ec) drawn downward?

It lags current by 90 degrees. This is why it points down (-90 degrees).

### Why are current vectors used to analyze a PARALLEL circuit?

Because the VOLTAGE is the SAME across all components.

All are EQUAL and IN PHASE with current, so that vector is the horizontal (X) axis.

### Why are voltage vectors used to analyze a SERIES circuit?

Because the CURRENT is the SAME across all components.

All are EQUAL and IN PHASE with voltage, so that vector is the horizontal (X) axis.

### Power Factor

The ratio of true power (in watts) to apparent power (in volt-amperes) in a REACTIVE circuit.

### The value of capacitive reactance _______ as frequency increases

decreases (inversely proportional)

High freq=low Xc

### Counter electromotive force (cemf)

Voltage induced in an inductor coil by the expansion and collapse of the magnetic field resulting from an applied voltage.

### CEMF characteristics

Always opposes applied voltage.

Greater inductance=greater cemf

Always 180 degrees out of phase with applied voltage.

### In a purely inductive circuit current ___ voltage.

LAGS - remember ELI the ICE man.

E(voltage) L(inductive circuit) I(current)

Current lags by 90 degrees.

### The opposition to current flow by an inductor in an AC circuit is

inductive reactance (Xl) measured in ohms

### Inductive reactances in series

When inductors are connected in series, the total inductive reactance is equal to the sum of the individual inductive reactance values