Current, Resistance, and Simple Circuits. A capacitor is a device used to store electrical energy. There are two different ways to arrange circuit.

Current, Resistance, and Simple Circuits

A capacitor is a device used to store electrical energy.

There are two different ways to arrange circuit components: Series

Current is constant, voltage varies Parallel

Current varies, voltage is constant

Review

Current – The flow of electric charges through a piece of material.

Throughout these notes, we are going to compare circuits to water. Current is like the speed that water is flowing.

Rapids would represent a large current.

Current is the rate at which charges flow through a specific area.

Current

It is conventional to assign the current as pointing in the same direction of flow for positive charges.

Unit: Ampere (Amp for short) Vector Quantity

Batteries don’t give electrons. They push the ones already there…

Current

Current

# of Charges

Duration (Time)

Resistance – A charged particle’s resistance to a change in motion in response to an external force.

Resistance is like the widening or shrinking of a pipe to change the rate of flow of water through a pipe.

Resistors are used to control the current in different parts of a circuit.

Resistance

Current, Resistance, and Voltage all affect each other.

Voltage is the push. Current is the flow. Resistance is the slowing down of current.

Ohm's Law Demo

Ohm’s Law

For Resistance: Unit: Ohm (Ω)

Scalar Quantity

Ohm’s Law

Voltage

Current

Resistance

Resistivity – An inherent property of a material and how much that material resists the flow of electron.

Resistivity

Resistivity

Length of Material

Cross-Sectional Area

TemperatureTemperature Coefficient of Resistivity

There is a continuous transformation of chemical energy in a battery into kinetic energy of the electrons.

Power – the rate of energy transfer.

Unit: Watts Scalar Quantity

Electrical Power

Direct Current Circuit (DC) – A circuit that has a current that is constant in magnitude and direction.

Alternating Current Circuit (AC) – A circuit that has current that is changing in magnitude and direction.

Electromotive Force – The maximum possible voltage that a battery can provide (Symbol: ε)

Direct vs. Alternating Current

Remember the symbols from last week: Wire Battery Capacitor Switch

And two new ones: Resistor Light Bulb

Circuit Design

Remember in a series Circuit: Current is the same everywhere. Voltage varies over each component.

Equivalent Resistance:

Resistors in Series

R1

R2 R3

Battery

Remember in a parallel Circuit: Current varies over each component. Voltage is the same everywhere.

Equivalent Resistance:

Resistors in Parallel

R1

R2

R3

Battery

Let’s take a look at why Current and Voltage change depending on the type of circuit we have.

Circuit Construction

Circuit Construction

Calculate the current and voltage delivered to each resistor in the circuit shown below.

Practice Problem

18 Volts

4 Ohms

2 Ohms

3 Ohms 1 Ohm