ElectricityElectricity

Currents, CircuitsCurrents, Circuits

Electricity that Electricity that movesmoves……

CurrentCurrent: The flow of electrons : The flow of electrons from one place to another.from one place to another.

Measured in Measured in amperesamperes (amps) (amps)KineticKinetic energy energy

How can we How can we controlcontrol currents? currents?

With With circuitscircuits..CircuitCircuit: is a : is a pathpath for the flow of for the flow of

electrons. We use electrons. We use wireswires..

There are 2 types of currents:There are 2 types of currents:

Direct Current (DC)Direct Current (DC) – Where – Where electrons flow in the electrons flow in the samesame direction in a wire. direction in a wire.

There are 2 types of currents:There are 2 types of currents:

Alternating Current (AC)Alternating Current (AC) – – electrons flow in electrons flow in differentdifferent directions in a wiredirections in a wire

There are 2 types of circuits:There are 2 types of circuits:

Series CircuitSeries Circuit: the components : the components are lined up along are lined up along oneone path. If path. If the circuit is broken, the circuit is broken, all all components turn off.components turn off.

Series CircuitSeries Circuit

There are 2 types of circuits:There are 2 types of circuits:

Parallel CircuitParallel Circuit – there are – there are severalseveral branching paths to the branching paths to the components. If the circuit is components. If the circuit is broken at any one branch, broken at any one branch, only only the components on that branch the components on that branch will turn offwill turn off..

Parallel CircuitParallel Circuit

What is Resistance?What is Resistance?

The The oppositionopposition to the flow of an to the flow of an electric current, producing electric current, producing heatheat..

The The greatergreater the resistance, the the resistance, the lessless current gets through. current gets through.

GoodGood conductors have conductors have lowlow resistance.resistance.

Measured in Measured in ohms.ohms.

What Influences Resistance?What Influences Resistance?

Material of wireMaterial of wire – aluminum and – aluminum and copper have low resistancecopper have low resistance

ThicknessThickness – the thicker the wire the – the thicker the wire the lower the resistancelower the resistance

LengthLength – shorter wire has lower – shorter wire has lower resistanceresistance

TemperatureTemperature – lower temperature has – lower temperature has lower resistancelower resistance

What is Voltage?What is Voltage?

The The measure of energymeasure of energy given to given to the charge flowing in a circuit.the charge flowing in a circuit.

The The greatergreater the voltage, the the voltage, the greater the force or “pressure”greater the force or “pressure” that drives the charge through the that drives the charge through the circuit.circuit.

Difference b/t Volts and AmpsDifference b/t Volts and Amps

Example – you could say that…Example – you could say that…AmpsAmps measure measure how muchhow much water water

comes out of a hose.comes out of a hose.VoltsVolts measure measure how hardhow hard the water the water

comes out of a hose.comes out of a hose.

Ohm’s LawOhm’s Law

Resistance = Voltage / CurrentResistance = Voltage / Current

Ohms = Volts / AmpsOhms = Volts / Amps

Practice with Ohm’s LawPractice with Ohm’s Law

OhmsOhms VoltsVolts AmpsAmps

44 100100 2525

1515 150150 1010

22 3030 1515

99 4545 55

66 4848 88

What are batteries?Batteries are composed of a chemical substance which can generate voltage which can be used in a circuit.

There are two kinds of batteries: dry cell and wet cell batteries. Below is an example of a dry cell.

The zinc container of the dry cell contains a moist chemical paste surrounding a carbon rod suspended in the middle.

Wet cell batteries are most commonly associated with automobile batteries.

A wet cell contains two connected plates made of different metals or metal compounds in a conducting solution. Most car batteries have a series of six cells, each containing lead and lead oxide in a sulfuric acid solution.

How is Electrical Power calculated?

Electrical Power is the product of the current (I) and the voltage (v)

The unit for electrical power is the same as that for mechanical power in the previous module – the watt (W)

Example Problem: How much power is used in a circuit which is 110 volts and has a current of 1.36 amps?

P = I V

Power = (1.36 amps) (110 V) = 150 W

How is electrical energy determined?

Electrical energy is a measure of the amount of power used and the time of use.

Electrical energy is the product of the power and the time.

Example problem:

E = P X time

P = I V

P = (2A) (120 V) = 240 W

E = (240 W) (4 h) = 960Wh = 0.96 kWh