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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