Alternating voltages and currents

Slides:



Advertisements
Similar presentations
Alternating-Current Circuits
Advertisements

Electric current DC Circuits AC Circuits. Lecture questions Electric current DC Circuits. Ohm's law Resistance and conductance Conductivity of electrolytes.
Measurement of Voltages and Currents
Lesson 17 Intro to AC & Sinusoidal Waveforms
1.3c Current Electricity Alternating Currents Breithaupt pages 74 to 79 November 14 th, 2010.
Mains Supply Noadswood Science, 2012.
We have been using voltage sources that send out a current in a single direction called direct current (dc). Current does not have to flow continuously.
AC Signals. Sinusoidal Signal  An ideal generator produces an induced emf that oscillates. Sine or cosine wave  The oscillation is characterized by.
1 Announcements l Bring motors to lab this week. l Bring eight 1N4001 diodes to lab per team. Get them at the Scientific Supply Store (2 nd Floor Sciences.
 Distortion – the alteration of the original shape of a waveform.  Function of distortion analyzer: measuring the extent of distortion (the o/p differs.
The Effective Value of an Alternating Current (or Voltage) © David Hoult 2009.
ECE 1100: Introduction to Electrical and Computer Engineering Notes 23 Power in AC Circuits and RMS Spring 2008 David R. Jackson Professor, ECE Dept.
AC Circuits (Chapt 33) circuits in which the currents vary in time
AC Waveform and AC Circuit Theory Md Shahabul Alam Dept: EEE.
6.1 Alternating current.
Electrical principles. The aim of today is to understand the average and RMS values in an AC circuit. Objectives: To know how alternating current is produced.
Electrical principles. Session 1 a.c circuits Objectives: To know how alternating current is produced To understand what average and RMS values are, in.
AC electric circuits 1.More difficult than DC circuits 2. Much more difficult than DC circuits 3. You can do it!
2.2 Alternating Current and Voltage
Alternating Current Electricity Lesson 11. Learning Objectives To know what is meant by alternating current. To know how to calculate the rms value of.
Electromagnetism Topic 12.2 Alternating Current. Rotating Coils Most of our electricity comes from huge generators in power stations. Most of our electricity.
1 AC Electricity. Time variation of a DC voltage or current 2 I V Current Voltage time t.
EE2010 Fundamentals of Electric Circuits Lecture 13 Sinusoidal sources and the concept of phasor in circuit analysis.
Class 34 Today we will: learn about inductors and inductance
Direct Current D.C. stands for direct current. Batteries supply d.c. With d.c. the current is always in travelling in the same direction. The current flows.
 Voltage can be produced such that, over time, it follows the shape of a sine wave  The magnitude of the voltage continually changes.  Polarity may.
Alternating Voltage and Current
Chapter 13 – Sinusoidal Alternating Waveforms Lecture 12 by Moeen Ghiyas 23/11/
AC Measurements Topics covered in this presentation:
AC/DC With your partner complete the card sort game on symbols and terms.
Announcements Midterm Exam next Friday In class, ~1 hr. Closed book, one page of notes Bring a calculator (not phone, computer, iPad, etc.) Practice problems.
As Unit 1 - Electricity What you need to know..  Current is the rate of flow of charged particles.  In metals these are conduction electrons, most electrons.
P.1 Book 4 Section 6.1 Alternating current Patterns formed by light emitting diodes A.c. and d.c. Check-point 1 Effective value of an a.c. Root-mean-square.
Dr. Michael Nasief.  Rotating electrical machines (ac generators)  Electronic oscillator circuits.
Announcements Midterm Exam next Wednesday Exam starts at 6 PM, ~1 hr. Closed book, one page of notes Bring a calculator (not phone, computer, iPad, etc.)
Chapter 8 Introduction to Alternating Current and Voltage.
Lesson 14: Introduction to AC and Sinusoids
SYLLABUS AC Fundamentals AC Analysis AC power Three phase circuit
The Effective Value of an Alternating Current (or Voltage)
Introduction to Alternating Current and Voltage
Network Circuit Analysis
Alternating Current – Learning Outcomes
What is direct current (DC)?
COVERAGE TOPICS AC Fundamentals AC Analysis AC power
6.1 Alternating current and power
Lecture 31 Sinsuoidal steady state power Related educational modules:
Harmonic Distortion Analyzer, Wave Analyzer and Function Generator
ALTERNATING CURRENT AND VOLTAGE
Chapter 22: AC Circuits Figure (a) Direct current. (b) Alternating current.
Chapter 23 ELECTRONICS.
Alternating Current Circuits
Chapter 11 Alternating Current.
Sinusoidal Waveform Phasor Method.
April 24th, 2006 AC Circuits PHYS 102
Electric Circuits Fundamentals
electronics fundamentals
The Effective Value of an Alternating Current (or Voltage)
CHAPTER 6 (BEE) AC Fundamentals
Higher Physics Electricity.
Key areas A.C as a current which changes direction and instantaneous value with time Calculations involving peak and r.m.s. values Determination of frequency.
Electric Current And Related Parameters
Diodes AIM: To understand diode characteristics
Electronics Fundamentals
ECE131 BASIC ELECTRICAL & ELECTRONICS ENGG
Electric Current And Related Parameters
Cfe Higher Physics Unit 3.1 Alternating Current and Voltage.
C H A P T E R 11 A.C. Fundamentals.
Household Electricity
Lesson Starter 06/03/19.
Presentation transcript:

Alternating voltages and currents

Alternating Potential Differences a.c. supply Most alternating voltages vary “sinusoidally”. Hence the wavy symbol!

The period T of the p.d. is the time taken for one complete wave or (cycle). The frequency of the supply is 1/T. So the frequency (f) of the supply is equal to the number of cycles in a second. The mains frequency in England is 50Hz .

Finding an average value for the a.c. current time The size of the current follows a similar pattern to the p.d. We need to be able to say what the “average” current is. If we take a simple mean for the current we get a value zero!

Measuring an a.c. current Ia.c. Ia.c. We compare the magnitude of the current in an a.c. circuit with that in a d.c. circuit. We do this in terms of the power dissipated through an exactly equal resistance. R Id.c.

R resistor in a.c circuit Same resistor in d.c. circuit When the power output from the two resistors is exactly the same we say that exactly the same current is flowing through the two resistors. The power formula tells us that power is the product of current and voltage P =IV In this form this relationship doesn’t help much as I and V in the a.c. circuit are both varying continuously. However substituting for V using V=IR yields P= I2R And the power through a given resistance can be seen to depend only on the current

R resistor in a.c circuit resistor in d.c. circuit R P=(Iac)2R So the power through the resistor must be proportional to the average value of I2 P=I2R This says that the power through the resistor is proportional to I2 This value is the root mean square current

Root mean square value of the current Current /I I0 Irms Time t It can be shown for a sine curve it can be shown that:

I2 mean square value i.e. average (I)2 value of the current (Irms)2

Sinusoidal voltage A similar argument for sinusoidal voltage change gives a similar result Voltage / V Root mean square value of the voltage V0 Vrms Time t

Peak to Peak Voltage Peak to peak voltage Voltage / V V0 Time t

Peak Voltage Peak voltage In this case the peak voltage is equal to the amplitude of the wave Voltage / V V0 Time t

Peak Voltage Peak voltage In this case the peak voltage is not equal to the amplitude of the wave Voltage / V Time t This diagram illustrate the difference between peak voltage and amplitude.

The Basic Oscilloscope

The oscilloscope The oscilloscope is a simple means of producing p.d/ time graphical displays. It is an immesly powerful tool becausse it can be used to capure very small intervals of time and tiny voltages.

The time interval represented by the horizontal distance across one square is (in this case) 0.2 s The horizontal distance is referred to as the “time-base”. It takes the spot 0.2 seconds to travel this distance at this setting

The p.d. scale on the oscilloscope is +1V per square The p.d, between the input terminals of the oscilloscope is zero volts

The p.d. input read by the oscilloscope is +1V

The p.d. input read by the oscilloscope is -1V i.e the input terminals of the oscilloscope have been reversed.

An a.c voltage is represented by a sinusoidal wave. On a time base of 1 ms with a voltage scale of 5V, What is the frequency of the a.c. signal? What is the peak voltage of the signal? The potential of the mains electrical supply oscillates in this way at a frequency of 50 Hz. This potential drives a current with the same frequency