Transcript Introduction to Engineering Session 68 Electrical Circuits

Introduction to Engineering
Electrical Circuits and Controls - 1
Agenda
 Introduction to electrical circuits,
controls and preparing simple
electrical drawings.
Agenda
Discuss basic concepts for electrical
circuits and controls.
Learn how to read and create simple
electrical drawings.
Electrical Drawings
 Electrical drawings provide a complete
description of the electrical circuitry for a
product.
 The purpose of a circuit diagram is to clearly
show how components are connected
electrically. This is not the same as showing
where components are physically, or how they
have been laid out on a circuit board.
 Standard symbols are used.
Symbols for Basic Components in a Circuit
resistor
inductor
capacitor
voltage source
current source
switch
Example: Single Use Camera Flash Circuit
Creating Electrical Circuit Diagram for a
Device - Flashlight
(Switch)
S
(Battery)
V
actual object
(Resistive
Load)
(Current)
R
I
electrical drawing
Electrons flow from (-) to (+); by convention,
current is said to flow in the opposite
direction.
Ohm’s Law
V = IR
The voltage change V (volts) across
any resistive load is equal to the
product of the current I (amps) and the
resistance R (Ohms).
Basic Relationship – Power Law
P = IV
Power dissipated P (watts) is
equal to product of the current I
(amps) and voltage V (volts)
Example 1 – Instructor Example
120 V
i=?
R = 12
ohms
Current
I = V/R = 120 V/12 Ohms = 10 amps
Power
P = V I= 120 V * 10 Amps = 1200 Watts
Example 2 – Student Example
240 V
I=
P=
I=?
R = 24 Ohms
Example 3 – Resistance of Light Bulbs
Without doing any calculations, which light
bulb has the lowest resistance?
75 W bulb at 120 V
150 W bulb at 120 V
Example 3 – Resistance of Light Bulbs,
calculate and compare
Calculate the resistance using Power Law and
Ohms Law. Use:
I = P / V (P = VI) & R = V / I
 Some groups do 75 W bulb
 Other groups do 150 W bulb
 Compare Results
Assignment #28
Do problem set 1 on electrical circuits
found in the assignment packet.