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EGR 1013 Circuit Components Batteries + +
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EGR 101 1
Egr 101
BatteriesIntroduction to Ohms Law
EGR 101 2
Where Does Current Come From?
• The free electrons in a conductor need to be replaced when they move through the conducting medium (the wire).
• These electrons are replaced by electrons from a source of energy such as a battery.
EGR 101 3
Circuit Components• Batteries
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EGR 101 4
Source of Voltage in a Battery
• A chemical reaction within the battery separates positive and negative ions(charged atoms)
• When the battery is connected to a circuit, the negative charge move toward the positive charge and a current is produced
• The amount of current is constrained by the resistance of the circuit
EGR 101 5
Example of A Battery
The source of energy E in (Joules) releases charges Q in (Coulombs)
Voltage (V) – the difference in potential that uses E = one Joule (J) of energy to move a charge Q = one coulomb (C).
EGR 101 6
Current Direction
We will adopt “Conventional Flow” for all of our work!
EGR 101 7
Mathematical Relation
• E: Energy required to move charges in Joules (J).
• Q: Charge value in Coulombs (C).• V: Voltage or potential difference across
the battery's posts in volts (V).•
Thus, V = E / Q.• In units: 1 Volt = 1 Joule/Coulomb
EGR 101 8
Team In-class Activity (15 minutes)
• A 10 V source uses 2 Joules of energy per second. Calculate the current being used by the source.
• Hint, turn the word problem into equations; write down what you know.
Solution
• V = E/Q• I = dQ/dt• Q = E/V• dQ/dt = (dE/dt)/V• V = 10 Volts• dE/dt = 2 Joules/sec• I = 2/10 Amperes = 0.5 A
EGR 101 9
EGR 101 10
When batteries areconnected with their polarities in the same direction, they are in a series-aiding arrangement.
Series Circuits
• A series circuit is one in which the same current flows through each element of the circuit.
EGR 101 11
Voltage Sources in Series
• Voltage sources in series add algebraically
• 1.5 + 1.5 + 1.5 = 4.5 V
EGR 101 12
EGR 101 13
When batteries areconnected with their polarities in theopposite direction, they are in a series-opposing arrangement.
Voltage Sources in Series
• Voltage sources in series add algebraically.
• 1.5 + (-1.5) + 1.5 = 1.5 V
EGR 101 14
EGR 101 15
In Class Activity
• What is the total voltage between terminals A and B in the figure below?
Which terminal is at a higher potential?
9V 4V 15V
A B
Units
• Current I in Amperes, e.g. 1.2 A• Voltage V in Volts, e.g. 6 V• Resistance R in Ohms, e.g. 5 Ω
EGR 101 16
EGR 101 17
Introduction to Ohm’s Law
• A 1 Ohm resistance limits the current to 1 Amp when 1 Volt is applied.
V = I.R
EGR 101 18
Ohm’s Law
• Three forms:
• Use the form that best describes the quantity that you are trying to determine
V IRVIRVRI
EGR 101 19
Determine the Current
RVI
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I
EGR 101 20
Determine the Voltage
IRV
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EGR 101 21
Determine the Resistance
IVR
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