Transcript Powerpoint #2 Circuits and Resistance

CIRCUITS AND RESISTANCE
RECALL:
Current
Potential
Difference
The flow of electrons
Causes electrons to
flow
Symbol
I
V
Units
Amps (A)
Volts (V)
Definition
Formula
(if applicable)
How measured
(if applicable)
I=Q
t
Ammeter
V=E
Q
Voltmeter
Circuits:
A circuit is made up of a
power supply, connecting
wires & various elements
that allow electrons to leave
a
power
source,
travel
through the elements &
return back to the power
source.
Common Electric Symbols


Battery/Power
Source
Bulb
Common symbols (cont’d)

Switch

Push-button
Switch
Resistor

Voltmeter

Ammeter

V
A
Circuits
Power Supply
A
v
Ammeter
Resistor
Voltmeter
Trick to help identify type of circuit:
Series:Pen follows wire
Types
of
Circuits:
Parallel: Pen can go in more than one direction

There are 2 types of circuits:
1.
 2.

SERIES
Series Circuit
Parallel Circuit
PARALLEL
Series or Parallel?
1.
2.
PARALLEL
SERIES
3.
4.
A
PARALLEL
SERIES
A
Resistance
Symbol: R
Units:Ohms, Ω
Resistance is how difficult it is for
current to flow
• A device with HIGH Resistance will have
very little current passing through it
• A device with low resistance will have a
large current passing through it
A resistor is used to slow current down
IF:
R is High than I is low
R is Low than I is high
Equivalent Resistance - Req

Equivalent Resistance is the
TOTAL resistance of a circuit



Symbol: Req
Units: Ohms = Ω
Formulae:
Series:
Req = R1 + R2 + R3 + …
Parallel:
1
1
1
1



...
Re q R1 R 2 R3
What is the equivalent
(Req) of the circuit below?
5W
3W
10 W
Type of circuit:
Series
Formula:
Req = R1 + R2 + R3
Req = 10 + 5 + 3
Req = 18 W
resistance
What is the equivalent
(Req) of the circuit below?
75 W
30 W
Type of circuit:
Series
Formula:
Req = R1 + R2
Req = 75 +30
Req = 105 W
resistance
What is the equivalent
resistance (Req) of the
circuit below?
10 Ω
15 Ω
Type of circuit: Parallel
Formula:
1 ÷ 0.1666 = 6Ω
1
1
1
 
Re q R1 R2
1
1 1
 
Re q 10 15
1
 0.1  0.0666
Re q
1
 0.1666
Re q
Re q  6W
What is the equivalent
resistance (Req) of the
circuit below?
15 W
5W
15 W
Type of circuit: Parallel
Formula:
1 ÷ 0.3333 = 3Ω
1
1
1
1
 

Re q R1 R2 R3
1
1 1 1

 
Re q 15 5 15
1
 0.0666  0.2  0.0666
Re q
1
 0.3333
Re q
Re q  3W
KEY POINTS

Symbols of circuit parts:



Voltmeter, Ammeter, Power Supply,
Resistor
Two types of circuits (series and
parallel)
Formula for Req (equivalent resistance)
Series – Req = R1 + R2 + R3
1
1
1
1



Parallel Req R 1
R2
R3
RECALL:
Resistance
Current
Potential
Difference
Definition
Slows current
down
The flow of
electrons
Causes
electrons to
flow
Symbol
R
I
V
Units
Ohms (Ω)
Amps (A)
Volts (V)
Formula
(if applicable)
R=V
I
How measured
(if applicable)
Calculated
I=Q
t
Ammeter
V=E
Q
Voltmeter