Electricity

Dpto. Tecnoloxía, IES de Pastoriza, Arteixo

ELECTRICITY REVISION

Basic elements in an electric circuit:Components that produce electric current (e.c.)Components that conduct an e.c.Components that transform an e.c.Components that control the flow of e.c.

Basic electric magnitudes:VoltageIntensityResistance

Ohm's Law



Components that produce e.c.:Batteries and generators

Components that conduct an e.c.:Wires of conductor materials.

Components that transform an e.c.:Electric motor, light bulb, electric fire, resistors

Components that control the flow of e.c.:Switches, circuit switches, push button N.O. and N.C.



Basic magnitudes :MAGNITUDE DEFINITION UNITS

RESISTANCEOpposition that materials offer to electric current flow.

OHMS (Ω)KΩ = 1000 Ω = 10 3 ΩMΩ = 1000000Ω = 106 Ω

INTENSITYNumber of charges that go through the section of a conductor per unit of time.

AMPS (A)mA = 0,001A = 10-3AμA= 0,000001A = 10-6A

VOLTAGEEnergy difference between both of the extremes of a conductor.

VOLTS (V)KV = 1000V = 103 VMV= 1000000V


ELECTRICITY REVISION RESISTORS

There are 2 types:

fixed resistors:

variable resistors:

fixed resistor Potentiometers


ELECTRICITY REVISION RESISTORS

Fixed resistors:

These resistors have a fixed value represented by a

colour code that we can observe over their surface.

The most common are those of coal, they are small

cylinders of graphite recovered with a film of paint

and they have two terminals to connect them.


VARIABLE RESISTORS POTENTIOMETERS

Its value can be changed with a cursor or turning an axle.The resistance varies from 0 ohms to a maximum value indicated at potentiometerApplications

Thermostat of a heatingVolume control of a radio


ELECTRICITY REVISION Ohm's law

Ohm's law relates the intensity that flows through a conductor whith its resistance and the applied voltage.

VI= ― R


SERIES CIRCUITS

They are circuits where components are connected

one behind the other.

There is a different tension in each component, but

through all circulates the same intensity.

Resolution:

R e = R

1 + R

2 + R

3 + … = ΣR


PARALLEL CIRCUITS

They are circuits where components are connected

with two common points.

Through each component circulates a different

intensity but all have the same voltage.

Resolution: 1 1 1 1 1 = + + = Σ R

e R

1 R

2 R

3 R


MIXED CIRCUITS

They are circuits that have components connected

either in series or in parallel.

Resolution:

There is not an only way to solve these circuits.

We have to calculate equivalent resistances by

sections.


POWER AND ENERGY

Power is the electric magnitude that measures the

consumed energy per unit of time.

We represent it by P and it is measured in watts

(W).

If in a component circulates an intensity I and it is

fed with a voltage V, then, the power that consumes

it is calculated like:

P = V · I


POWER AND ENERGY

Power is a characteristic of all electrical devices.All electrical appliances present the relation of their electrical characteristics. We refer to that like nameplate.

Voltage

Power

Frecuency


POWER AND ENERGY

Energy consumed by an electrical device is determined by its power and the time in which it is running:

E= P·tConsumed electrical energy it is measured in W·s or in KW·hIf an electrical appliance is has a voltage of 230 V and consumes 640 W, then we can calculate its resistance like: R=V2/PThen R = 2302/640 = 82,65 Ω


POWER AND ENERGY

The consume in the electric bill is measured in kWh (power in kW and time in hours)If we multiply by the price of a kWh, we obtain the cost of use of that electrical appliance.Example: The cost of use of a hairdryer of 2200 W running during 30 minutes is

P = 2200 W = 2,2 kW

t = 30 min = 0,5 h

E = P.t = 2,2 . 0,5 = 1,1 kWh (consumed energy)

If the price of a kWh is 0.12 €, then the cost is: 1,1 x 0,12 = 0,13 €

Electricity

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