20.1 Schematic
Diagrams and Circuits
p730 - 735
Essential Questions
 How does the wiring in a circuit change its ability
to supply power to devices?
 How do we represent physical circuit elements in
schematic drawings?
Objective(s): We will be able
to…
 Interpret and construct circuit diagrams.
 Identify circuits as open or closed.
 Deduce the potential difference across the
circuit load, given the potential difference
across the battery’s terminals.
Agenda:
 Warm-Up
 Recap what happened on Friday.
 Reminder: Chapter 19 Test Tomorrow.
 Introduction to Circuit Diagrams
 Notes:
 Schematic Diagrams
 Circuits and short circuits
 EMFs
Warm Up
 The following drawings are used in circuit
diagrams. List what you think each object
represents.
•Wire
•Battery/D
C Source
•Resistor
•Switch
•Light Bulb
•Plug
•Capacitor
Schematic Diagrams
 A diagram that is used to
represent the construction
of an electrical apparatus is
a schematic diagram.
Sometimes called a circuit
diagram.
 They are used to determine
how parts in an electrical
device are arranged, and
to help understand how
they work.
Schematic Diagram Symbols
 Wire or conductor
Schematic Diagram Symbols
 Resistor or circuit load (Overall resistance.
Discussed more in a minute.)
Schematic Diagram Symbols
 Bulb or lamp
Schematic Diagram Symbols
 Plug
Schematic Diagram Symbols
 Battery
Schematic Diagram Symbols
 Switch
Schematic Diagram Symbols
 Capacitor
Electric Circuits
 An electric circuit is a
pathway through which
charges can be conducted.
 Circuits (and switches) must
be closed to complete the
pathway, otherwise charges
will not flow. Light switch on.
 Open circuits conduct no
electricity. Light switch off.
Electrical Circuits
 All circuits consist of two things…
 A source of potential difference
(electrical energy), like a battery,
and…
 A load: an element or group of
elements in a circuit that dissipates
energy.
Light Bulbs
 Light bulbs themselves are a
complete circuit with a
resistor.
 The filament acts as a resistor,
converting electrical energy
into internal energy and thus
heat and light.
Short Circuits
 Without a load (bulb or resistor), a
circuit has very little resistance.
 And therefore, very high current.
 This is called a short circuit.
 Most wires overheat when they short
circuit (think of the battery and the
paperclip). DANGEROUS!
 This is why we have fuses and circuit
breakers.
Electromotive Force (emf)
 Literally, the force that moves electrons.
 Any device that increases the flow of charge in
a circuit is a source of emf, the energy per unit
charge supplied by the source.
 In real life, the terminal voltage (actual potential
difference from the battery) is less than its emf
due to internal resistance.
 The amount of power the battery actually supplies
is less than what it should, because some of the
energy is wasted internally.
Terminal Voltage
 The potential difference across a load equals the
terminal voltage.
 Meaning: if a battery supplies 1.5 volts of
potential difference,
 then the voltage across the resistor, bulb, or
collection of resistors and bulbs etc. is 1.5 volts.
 No energy created or destroyed.
Recap
 Circuit diagrams are used to represent and
analyze the composition of electric devices.
 Open circuits do not have a complete pathway,
so they do not conduct electricity. Closed
circuits complete the pathway, so they do
conduct electricity.
 The voltage across the load of a circuit is the
same as the voltage supplied by the battery.
Homework
 Tonight: Finish study guide.
 Due Wed: p 735 #1-5