1. 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.
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2. Circuit Components
Batteries + +
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3. 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 charges move toward the positive terminal and a current is produced
The amount of current is constrained by the resistance of the circuit
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4. 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).
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5. Current Direction
We will adopt “Conventional Flow” for all of our work!
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6. Mathematical Relationship
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
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7. 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.
V = 10 = w (J)/Q (C); P = 2 W = 2 J/s
Solving for Q gives Q = W/V
Then substituting into
I = Q/t gives I = W/(V*T) = 2/10 = 1/5 A
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8. When batteries are connected with their
polarities in the same direction, they are in a series-aiding arrangement.
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9. opposite direction, they are in a series-opposing arrangement.
When batteries are
connected with their
polarities in the
opposite direction, they are in a series-opposing arrangement.
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10. In Class Activity
What is the total voltage between terminals A and B in the figure below? Which terminal is at a higher potential? A B 9V 4V
15V
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11. Introduction to Ohm’s Law
A 1 Ohm resistance limits the current to 1 Amp when 1 Volt is applied.
V = I.R
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12. Ohm’s Law
Three forms:
Use the form that best describes the quantity that you are trying to determine
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13. Determine the Current I + _
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14. Determine the Voltage + _
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15. Determine the Resistance+ _
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