EGR 101 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.

EGR 101 2

Circuit Components• Batteries

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+

EGR 101 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

EGR 101 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).

EGR 101 5

Current Direction

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

EGR 101 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

EGR 101 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.

EGR 101 8

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

EGR 101 9

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

EGR 101 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?

9V 4V 15V

A B

EGR 101 11

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 12

Ohm’s Law

• Three forms:

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

V IR

VI

RV

RI

EGR 101 13

Determine the Current

R

VI

+

_

I

EGR 101 14

Determine the Voltage

IRV

+

_

EGR 101 15

Determine the Resistance

I

VR

+

_