More about electricity an electronics

Unit 6 continuation

ALTERNATING AND DIRECT CURRENT: AC DC

DIRECT CURRENT

It’s the type of current, we get from batteries.

IT’ S ALWAYS THE SAME

ALTERNATING CURRENTIMAGINE A BATTERY CHANGE BETWEEN THE POSITIVE TERMINAL AND THE NEGATIVE.

ALTERNATING CURRENT is the type of current we get from a plug or the main supply.

WE DON’T GET ALWAYS THE SAME VALUE, BECAUSE ELECTRONS CHANGE THE SENSE OF THEIR DIRECTION. THEY CHANGE IT 50 TIMES A SECOND.

WHY WE USE ALTERNATING CURRENT?

• Because this kind of electricity is easier to transport than the direct one

ELECTRIC ENERGY

What was voltage?

• The energy that gives a battery to the electrons to keep then moving through the wire.

• This energy is given to a bulb, a resistor, a buzz, ...

• In these components is transformed into another way of energy.

How can we measure this energy?

• The energy that is consumed by an electrical appliance is calculated knowing the current(I) that pass through it, the voltage (V) that supports and the time working (t):

• E = V · I · t• Unit: Jule, J

Something about electrical appliances

• Motors transform the electricity in movement• Bulbs transform the electricity in light• Resistors transform the energy in heat, so

they are used in heaters

ELECTRIC POWER

• The capacity of an electrical appliance to transform energy in a period of time.

• UNIT: Watt, W

• It can be calculate by : P = V ·I

How can be related energy and power?

• Once we know the power of a receiver, it’s easy to calculate the electric energy consumed by it:

• E = P · t

El kilowatio hora y la factura de la luz

• If you express power in Kw and time in hours, you will get a new unit to energy, kwh.

• These is the unit that measure the consume of energy at home.

ELECTRONIC COMPONENTS

RESISTORS

Variable resistors o potentiometers

• It’s a kind of resistor with a value that can be adjusted between a cero and a maximum value given by the manufacturer

Resistor that depends of a physical property• Light Dependent Resistors, LDR, the more light

it receives, the less resistor it has.• Thermistors:– NTC (Negative Temperature Coefficient), the

resistor decreases when the temperature increases

– PTC (Positive Temperature Coefficient), the resistor increases when the temperature increases

light sensor making steps- www.ldrengineering.org, www.circu.flv

CAPACITORS

• DIODES