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Physical Science
Grade 10
www.learnxtra.co.za
SESSION 10: ELECTRIC CIRCUITS
KEY CONCEPTS:
In this session we will focus on:
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
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Potential Difference (emf)
Current
Circuit Diagrams
Resistance
Resistors in Series
Resistors in Parallel
X-PLANATION
Potential Difference (emf):
Definition: Potential difference is the work done per unit charge.
The unit of potential difference is the volt (V), which is defined as 1 joule per
coulomb.
Emf: Potential difference across the terminals of a battery that is not in a complete
circuit.
Maximum amount of work per coulomb of charge the battery can do.
Measured with a voltmeter
Connected in parallel
Current:
Definition: The rate at which charges moves past a fixed point in a circuit.
The unit of current is the ampere (A) which is defined as one coulomb per second
Measured with an ammeter
Connected in series
Example 1:
An amount of charge equal to 45 C moves past a point in a circuit in 1 second, what
is the current in the circuit?
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Example 2:
Write definitions for each of the following:
a.
b.
c.
ampere
coulomb
voltmeter
Circuit Diagrams:
Component
Symbol
Usage
Light Bulb
Glows when charge moves through it.
Battery
Provides energy for charge to move.
Switch
Allows a circuit to be open or closed.
Resistor
Resists the flow of charge.
Voltmeter
Measures potential difference.
Ammeter
Measures current in a circuit
Connecting Lead
Connects circuit elements together.
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Resistance:
Definition: Resistance slows down the flow of charge in a circuit. The unit of
resistance is the ohm (Ω) which is defined as a volt per ampere of current.
Resistors in Series:
-
Current is the same everywhere
Voltage is divided
Resistance increases
Resistors in Parallel:
-
Current is divided
Voltage is the same
Resistance decreases
X-AMPLE QUESTIONS
Question 1:
Three identical light bulbs A, B and C are connected in an electric circuit as shown in
the diagram below.
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Physical Science
Grade 10
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a.
b.
c.
How bright is bulb A compared to B and C?
How bright are the bulbs after switch S has been opened?
How do the currents in bulbs A and B change when switch S is opened?
Question 2:
There are 3 resistors in parallel with resistances of 3 Ω, 4 Ω and 11 Ω. What is the
total resistance of the parallel combination?
Question 3:
The same three resistors as above are now arranged in series, 3 Ω, 4 Ω and 11 Ω.
What is the total resistance of the series combination?
Question 4:
In a series circuit there are 3 resistors with voltages of 2 V, 5 V and 8 V, what is the
voltage across the battery in the circuit?
Question 5:
In a parallel circuit there are 3 resistors with voltages of 2 V, 2 V and 2 V, what is the
voltage across the battery in the circuit?
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