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EGR 101 1 Egr 101 Batteries Introduction to Ohms Law
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EGR 1011 Egr 101 Batteries Introduction to Ohms Law.

Jan 20, 2018

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Page 1: EGR 1011 Egr 101 Batteries Introduction to Ohms Law.

EGR 101 1

Egr 101

BatteriesIntroduction to Ohms Law

Page 2: EGR 1011 Egr 101 Batteries Introduction 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.

Page 3: EGR 1011 Egr 101 Batteries Introduction to Ohms Law.

EGR 101 3

Circuit Components• Batteries

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Page 4: EGR 1011 Egr 101 Batteries Introduction to Ohms Law.

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

Page 5: EGR 1011 Egr 101 Batteries Introduction to Ohms Law.

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).

Page 6: EGR 1011 Egr 101 Batteries Introduction to Ohms Law.

EGR 101 6

Current Direction

We will adopt “Conventional Flow” for all of our work!

Page 7: EGR 1011 Egr 101 Batteries Introduction to Ohms Law.

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

Page 8: EGR 1011 Egr 101 Batteries Introduction to Ohms Law.

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.

Page 9: EGR 1011 Egr 101 Batteries Introduction to Ohms Law.

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

Page 10: EGR 1011 Egr 101 Batteries Introduction to Ohms Law.

EGR 101 10

When batteries areconnected with their polarities in the same direction, they are in a series-aiding arrangement.

Page 11: EGR 1011 Egr 101 Batteries Introduction to Ohms Law.

Series Circuits

• A series circuit is one in which the same current flows through each element of the circuit.

EGR 101 11

Page 12: EGR 1011 Egr 101 Batteries Introduction to Ohms Law.

Voltage Sources in Series

• Voltage sources in series add algebraically

• 1.5 + 1.5 + 1.5 = 4.5 V

EGR 101 12

Page 13: EGR 1011 Egr 101 Batteries Introduction to Ohms Law.

EGR 101 13

When batteries areconnected with their polarities in theopposite direction, they are in a series-opposing arrangement.

Page 14: EGR 1011 Egr 101 Batteries Introduction to Ohms Law.

Voltage Sources in Series

• Voltage sources in series add algebraically.

• 1.5 + (-1.5) + 1.5 = 1.5 V

EGR 101 14

Page 15: EGR 1011 Egr 101 Batteries Introduction to Ohms Law.

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

Page 16: EGR 1011 Egr 101 Batteries Introduction to Ohms Law.

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

Page 17: EGR 1011 Egr 101 Batteries Introduction to Ohms Law.

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

Page 18: EGR 1011 Egr 101 Batteries Introduction to Ohms Law.

EGR 101 18

Ohm’s Law

• Three forms:

• Use the form that best describes the quantity that you are trying to determine

V IRVIRVRI

Page 19: EGR 1011 Egr 101 Batteries Introduction to Ohms Law.

EGR 101 19

Determine the Current

RVI

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I

Page 20: EGR 1011 Egr 101 Batteries Introduction to Ohms Law.

EGR 101 20

Determine the Voltage

IRV

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Page 21: EGR 1011 Egr 101 Batteries Introduction to Ohms Law.

EGR 101 21

Determine the Resistance

IVR

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