Electricity

Introduction • What is electricity for you?

• What would happen if we didn’t have electricity?

– Write several sentences with the things you do in your daily life with electricity.

• Example.

– My alarm clock goes off at 8:00.

– I switch on the light of my room.

What is electricity?

• Electricity is a form of energy produced by the movement of electrons.

• The concept of electricity includes all the phenomena related to the electric charges.

• Matter is formed by atoms, which contain inside smaller particles with electric charges.

• Electrons (-) • Protons (+) • Neutrons (no charge)

Attraction ----- Repulsion

Conductors and insulators • Conductors are materials that allow electric current to pass through them.

• Insulators are materials that don´t allow electric current to pass through them.

Conductors and insulators

The nail acts as a conductor. It allows electricity to flow through The marbles act as an insulator. It does not allow electricity to flow through.

Electric circuits • An electric circuit is a set of connected component through which an electric current circulates.

• Component of electric circuits: – Generator – Wire conductor – Control component – Protection component – Appliances (receptors)

Electric circuits: GENERATOR • A generator provides the energy necessary to move electrons.

Electric circuits: WIRE CONDUCTOR Wires conductors connect the elements of a circuit.

Electric circuits: Receptor • The receptor are the components that transform electrical energy into another type of energy.

Electric circuits: Control components • Control component stop, start or change the direction of the electric current.

Electric circuits: Protection components • Protection components stop the current when it is too strong or it escapes.

Electric circuits. Symbols (I) Generator

Battery Battery association

Conductors: When two conductors are crossed without any contact we indicate it with a curve

Electric circuits. Symbols (II) Control elements

Push button Switch 3-ways-Switch

Electric circuits. Symbols (III) Protection elements Fuse Receptors: Lamp: Produces light

Resistances: they have two symbols Bell: Produces sounds

Motors: Produces motion

Effects of electric current: Heat • When an electric current flows through a material, the resistance of the material transforms some electric energy into heat. This is called the JOULE EFFECT.

Effects of electric current: Light • There are many types of bulbs.

– In the “incandescent light bulbs” current passes through a filament (resistance) which shines.

– Fluorescent lamps and highintensity discharge lamps consume less power. They are more expensive.

– LED’s (light-emitting diodes) are the most energy efficient.

Effects of electric current: Motion Motors transform electrical energy into motion.

They are based on the forces of attraction and repulsion between a magnet and a conductor wire placed in one or more loops inside it.

ELECTRIC MAGNITUDES In order to understand electricity we have to know first the main electric magnitudes:

VOLTAGE (TENSION)

CURRENT (INTENSITY) RESISTANCE

ELECTRIC MAGNITUDE. VOLTAGE (I) • Voltage or tension is the force that moves the electrons along the circuit.

• The unit of tension is the volt (V); the symbol for volt is “V”.

ELECTRIC MAGNITUDE. VOLTAGE (II) To understand what voltage is, we can imagine the tension as the inclination of a river. A river coming down from the mountains has a steep inclination, so the water moves with a lot of force. The tension or force is strong.

ELECTRIC MAGNITUDE. VOLTAGE (III) Another example to understand what voltage is. In this two tanks we can see that the stream will have more strength if there is more water in the tank. It’s similar to what happened to the electricity.

More water pressure

Less water pressure

ELECTRIC MAGNITUDE. CURRENT (I) • Current or Intensity is the amount of electrons that flow along the circuit.

• The unit of current is the amp (A); the symbol for amp is “A”.

Higher intensity

Lower intensity

ELECTRIC MAGNITUDE. CURRENT (II) • To understand what current is, we can imagine the electrons flowing in the circuit as water flows in a river.

• If there is a lot of water flowing downstream, the current is big.

ELECTRIC MAGNITUDE. RESISTANCE (I) Resistance is the opposition to the movement of electron through a conductor.

It is represented by letter R and is measured in Ohms (ď —) Higher Resistance

Lower Resistance

ELECTRIC MAGNITUDE. RESISTANCE (II) To understand what resistance is, we can imagine receptor (which have resistance) as rocks in a river. They make the flow of the water difficult.

Ohm’s law • George Simon Ohm discovered that current, tension and resistance are related:

• We can re-write the equation to calculate the tension, current or the resistance:

Ohm’s law Examples • If the circuit has a battery of 6V and a resistance of 3Ω, then the current is ???

I = V/R = 6/3 = 2A. • If the circuit has a battery of 6V, and the current is 3A, then the resistance of the appliance is ????

R = V/I = 6V / 3A = 2Ω

• If the circuit has a resistance of 3Ω, then the current is 3A the tension is ?????

V = I*R = 3*3 = 6V.

Electric power • Power (P) is the amount of energy consumed or produced.

• Watt (W) is the unit of the Electric Power and it express the energy consumed per time unit of an electric device

P  VI

P= Power (Watts W) V= Voltage (volt V) I= Current (ampere A)

Electric power At home all plugs have 230 Volts, so if we know the Power of a bulb lamp of 100W we can calculate the Current through the lamp.

P  100W

P  VI

V  230 V

P I V 100 I 230 I  0,34A

Electric Energy • In order to know how many electric energy has been consumed in kwh, we have to multiply the Electric Power and the hours of use.

E  Pt

E= Electric energy (Kwh) P= Power (kw) t= Time (h)

Electric Energy • Let’s calculate how much energy are when we use a washing machine for 2h if it consumes 1500W P  1500W  1,5kw Time  2 h

E  Pt E  1,5  2 E  3kwh

Sumary MAGNITUDE

SIMBOL

UNIT

ECUATION

TENSION

V

Volts (V)

V=I*R

CURRENT

I

Amps (A)

I=V/R

RESISTANCE R

Ohms (Ω)

R=V/R

POWER

P

Watts (W)

P= I*V ó P=E/t

ENERGY

E

kWh

E=P*t