Electric Current6.2

Current and Voltage Difference

Electric Current-The net movement of electric charge in a single direction. Measured in Amperes (A)

One Ampere is equal to 1 coulomb per second

If there is no current, there is no NET movement Movement forward=movement backward=movement side-to-side

When an electric current is applied, there is still backward and forward movement, but the electrons drift in the direction of the current. Net movement

Before Current is Applied

After Current is Applied

Current and Voltage Difference

Related to the force that causes electric charges to flow. From area of high voltage to low voltage

Measured in volts (V)

Electric Circuits A closed path that electric current follows

Battery, wire, lightbulb

Current and electron flow For historical reasons, we think of current as flow of positive charges

Positive charges do not flow

Due to this, current is in the opposite direction of electron flow

Electrons flow from lower to higher voltage

Current is from higher to lower voltage

Batteries

2 Main Types: Dry-cell

Wet-cell

Dry-Cell Batteries

Carbon Rod (positive)

Zinc Container (negative)

Moist paste (electrolyte)

Allows electrons to flow

Batteries in flashlights

Metals can be different

Lithium, carbon, and lithium

solution

Cell phone battery

Wet-cell Battery

2 connected plates made of different metals in an electrolyte

Unlike the paste in dry-cells, the wet-cell has a liquid

Has many cells connected together.

Most common type is lead-acid

Lead and Lead dioxide in sulfuric acid solution

Electrical Outlets

The 2 holes of an outlet have a voltage difference In the U.S. usually 120 V

Resistance

Tendency of object to resist flow of electrons Takes some of the flowing electrons from the current

Measured in ohms (Ω) This symbol is the capital form of the Greek letter “Omega”

This is why batteries charging get warm The resistor is taking some of the electrons, and converts the

chemical energy to thermal energy

Ohm’s Law

Current(A)=Voltage difference(V)/resistance(Ω) Current is measured in Amps (A)

Where I is current

Example Problem

The voltage difference in a graphing calculator is 6V, and the resistance is 1,200 Ω. What is the current through the batteries of the graphing calculator?

Knowns: V=6V, R=1200 Ω

Unknown: I=?

Equation:

Solve:

=0.005 A

Equations

Solve for V

Solve for R

Guided Practice

An object has a resistance of 60 Ω as a current of 2 A goes through it. What is the voltage difference across the object?

You Try It!

The voltage in a device is 50 V, and the resistance is 5 Ω. What is the current in the device?

Types of Current

Alternating Current (AC) Type found in household electrical outlets

Changes direction

Direct Current (DC) Found in battery-powered devices

Does not change direction

Converters change types (ACDC)