The document provides an overview of electric circuits and potential difference for a grade 9 science class. It introduces series and parallel circuits, defines electric potential difference, and discusses how to measure potential difference in series and parallel circuits. Key points covered include the relationships between voltages in series and parallel circuits and equations relating voltage, energy, charge, and work. Students are directed to practice questions and supplemental video resources are provided.

1. Unit 2Unit 2
Review of Electric Circuits
& Potential Difference in Circuits
Modified for Grade 9 ScienceModified for Grade 9 Science

2. S e r ie s C ir c u it
( O n e L o o p )
 In Grade 9 Science, you are introduced to twoIn Grade 9 Science, you are introduced to two
types of circuits: _________ & ____________ .types of circuits: _________ & ____________ .
These are shown above.These are shown above.
 Label the symbols used in the two diagramsLabel the symbols used in the two diagrams
above. Your textbook has more symbols listedabove. Your textbook has more symbols listed
on page 551.on page 551.
P a r a lle l C ir c u it
( T w o o r M o r e L o o p s )

3. Electric Potential Difference (PD)
Often calledOften called potential difference, or, or
justjust voltage, there are various, there are various
ways we can define this quantity.ways we can define this quantity.
Consider the diagram on the right.Consider the diagram on the right.
The voltmeter will measure the PDThe voltmeter will measure the PD
across the light which is turnedacross the light which is turned
___ . The reading (in Volts) would___ . The reading (in Volts) would
be equal to:be equal to:
1.) V = ΔEQ/Q oror 2.) V = W/Q
The first equation hasThe first equation has V, or PD,, or PD,
equal to the energy difference (inequal to the energy difference (in
Joules) before and after aJoules) before and after a load
divided by the amount of chargedivided by the amount of charge
((Q) that went through the load.) that went through the load.
V

4. TheThe second equation uses the work required (inuses the work required (in
Joules) to move charge through the load divided byJoules) to move charge through the load divided by
the amount of charge moved. Charge (Q) isthe amount of charge moved. Charge (Q) is
measured in __________ .measured in __________ .
All loads (motors, lights, resistors) haveAll loads (motors, lights, resistors) have electrical
resistance, which resists (or opposes) the flow of, which resists (or opposes) the flow of
current. As such, it takes work to move electriccurrent. As such, it takes work to move electric
charge through a load. We usually assume thatcharge through a load. We usually assume that
connecting wires have no resistance, so the voltageconnecting wires have no resistance, so the voltage
across a wire in a “live” circuit would be ________ .across a wire in a “live” circuit would be ________ .
Also, from slide 2, we can see that a voltmeter mustAlso, from slide 2, we can see that a voltmeter must
be connected in _________ with a load.be connected in _________ with a load.
From the equations, we see thatFrom the equations, we see that 1 Volt == 1 __ /__ ..

5. Measuring PD in a
Series Circuit
InIn Fig A, there is one, there is one
light bulb. Here,light bulb. Here,
the relationshipthe relationship
betweenbetween V1 andand V2
is: ________is: ________
InIn Fig B, there are, there are
two identical lighttwo identical light
bulbs. Thebulbs. The
relationshiprelationship
betweenbetween V1 ,, V2 andand
V3 is: ____is: ____
________________________
F ig u r e A
V 1
V 2
V 1
V 3
V 2
F ig u r e B

6. The PD across the battery is calledThe PD across the battery is called
the source PD orthe source PD or VS . The rule. The rule
for afor a series circuit is:is:
VS = V1 + V2 +…+ VN , where
there are N loads in series.
The diagram shows threeThe diagram shows three
voltmeters on the parallel cct.voltmeters on the parallel cct.
The relationship between theThe relationship between the
three valuesthree values V1 ,, V2 andand V3 is:is:
___________________ .___________________ .
The rule for a parallel circuit is PDThe rule for a parallel circuit is PD
is equal across ais equal across a branch of the
circuit.

7. In the following diagram, allIn the following diagram, all
lights are identical. Thelights are identical. The
relationship between therelationship between the
voltages (PD’s) acrossvoltages (PD’s) across
each bulb is:each bulb is:
__________________________________________ V 1
V S
V 2
V 3

8. Practice Questions
Grade 9 electricity w/b, page 22: Attempt allGrade 9 electricity w/b, page 22: Attempt all
questionsquestions

9. VideosVideos
 https://www.youtube.com/watch?v=z8qfhFXjsrwhttps://www.youtube.com/watch?v=z8qfhFXjsrw
 https://www.youtube.com/watch?v=8jB6hDUqN0Yhttps://www.youtube.com/watch?v=8jB6hDUqN0Y
 https://www.youtube.com/watch?v=8lMO7VAyEkYhttps://www.youtube.com/watch?v=8lMO7VAyEkY
 https://www.youtube.com/watch?v=-w-VTw0tQlEhttps://www.youtube.com/watch?v=-w-VTw0tQlE
 https://www.youtube.com/watch?v=5laTkjINHrghttps://www.youtube.com/watch?v=5laTkjINHrg
 https://www.youtube.com/watch?v=uUTHMcjtQCchttps://www.youtube.com/watch?v=uUTHMcjtQCc
 https://www.youtube.com/watch?v=ekRwjDzie4shttps://www.youtube.com/watch?v=ekRwjDzie4s

10. VideosVideos
 https://www.youtube.com/watch?v=z8qfhFXjsrwhttps://www.youtube.com/watch?v=z8qfhFXjsrw
 https://www.youtube.com/watch?v=8jB6hDUqN0Yhttps://www.youtube.com/watch?v=8jB6hDUqN0Y
 https://www.youtube.com/watch?v=8lMO7VAyEkYhttps://www.youtube.com/watch?v=8lMO7VAyEkY
 https://www.youtube.com/watch?v=-w-VTw0tQlEhttps://www.youtube.com/watch?v=-w-VTw0tQlE
 https://www.youtube.com/watch?v=5laTkjINHrghttps://www.youtube.com/watch?v=5laTkjINHrg
 https://www.youtube.com/watch?v=uUTHMcjtQCchttps://www.youtube.com/watch?v=uUTHMcjtQCc
 https://www.youtube.com/watch?v=ekRwjDzie4shttps://www.youtube.com/watch?v=ekRwjDzie4s