 # Electricity.

## Presentation on theme: "Electricity."— Presentation transcript:

Electricity

20.1 Electric Charge & Static Electricity

Force Electric forces – attractive or repulsive What does this mean?

Opposites attract

Like charges repel

And remember….

Electric Fields Strength of a field depends on:
the charge produced by the field the distance of field

Static Electricity DEFINITION:
Net accumulation of electric charges on an object. IN OTHER WORDS: Electrons that are moved from 1 place to another usually by rubbing, brushing or no contact.

Static charges work 3 ways
Friction Contact Induction

Friction Since opposite charges attract, the electrons move from the hair to the comb. The comb is now negatively charged by FRICTION.

For the visual learners . . .

Contact Van deGraaff generator has a – charge at top. Touching top would make the object – charged. The object is now negatively charged by CONTACT.

Induction - charges in hand cause the + charges in the doorknob to move to the opposite side (opposites attract) Charge has been transferred by INDUCTION.

For the visual learners….

Static Discharge When a pathway that charges can move through forms suddenly. Ie: lightening, touching a doorknob

Attract or Repel? Attract

Attract or Repel? Repel

What’s the best thing about static electricity?

Lecture 20.2                         You need a calculator

20.2 Electric Current & Ohms’s Law

Current The flow of electrons through a wire or a conductor.
SI unit = (Amps) A

2 types of current A/C – alternating current D/C – direct current
ie: by plugging into the household wiring D/C – direct current ie: batteries

Conductor DEFINITION: Material that allows electrons to move easily through it. IN OTHER WORDS: Just like a train conductor moves cars from one track to another track, conductors move electrons from one place to another.

Which metal is the best conductor for your internet connection?

Copper? Silver?

Insulator DEFINITION: Material that does not allow electrons to move through it. IN OTHER WORDS: Just as a potholder insulates you from heat, electrical insulators slow down or resist the flow of electricity.

Conductor or Insulator ?
Glass

Conductor or Insulator ?

Conductor or Insulator ?
Ceramic

Conductor or Insulator ?

Conductor or Insulator ?
Copper

Conductor or Insulator ?

Conductor or Insulator ?
Wood

Conductor or Insulator ?
Although uncommon, there are a number of insulator styles made from wood.  One type was made from the dense wood lignum vitae for the San Francisco trolley system.

Everyday examples of conductors and Insulators

To sum them up….. silver glass copper rubber gold oil aluminum asphalt
Conductors: silver copper gold aluminum iron steel brass bronze mercury graphite dirty water concrete Insulators: glass rubber oil asphalt fiberglass porcelain ceramic quartz (dry) cotton (dry) paper (dry) wood plastic air pure water

Mini Quiz The build up of charges on an object is called?
Electrons do not move through… Electrons move easily through materials called … Static Electricity Insulators Conductors

Resistance DEFINITION: the tendency for a material to oppose the flow of electrons, changing energy into thermal energy and light. SI unit = Ohm’s (W) See pg Fig. 8

What effects resistance?
Temperature Thickness Length

Think of a common household item that has a resistor
Something we use in class?

Potential Difference - Voltage
DEFINTION: Difference in potential between 2 different places. IN OTHER WORDS: It is the amount of work that must be done to carry a charge from one point to another.

A source of potential difference must keep the current flowing.

Ohm’s Law Potential difference = current x resistance
V (volts) = I (amperes) x R (ohms) Compare to: Water in a Hose Electricity is: DC in a Wire Electrical Units Symbol pressure potential (V) Volts V rate of flow current (I) Amps (or Amperes) A friction resistance (R) Ohms W

How do you remember the formula?
…..if this helps, use it.

Practice problems resistance – R = 75 ohms voltage – V = 110 volts
A 75 ohm circuit is powered by a 110-Volt energy source.  What is the current flowing in this circuit? First we identify the information that we are given in the problem: resistance – R = 75 ohms voltage – V = 110 volts Need to know amps 110V = I x 75 ohms (rearrange formula) Amps = 110 volts / 75 ohms (W) 1.5A

Practice problems resistance = 250 ohms current = 0.95 amps
What is the voltage of a circuit with a resistance of 250 ohms and a current of 0.95 amps? First we identify the information that we are given in the problem: resistance = 250 ohms current = 0.95 amps Need to know volts V= 250 ohms x 0.95 amps Volts = 250 ohms x 0.95 amps 237.5V

Mini Quiz ___ is a flow of electrons thru a wire or conductor. Current
A current must have a constant flow of ___ Current Potential Difference

Mini Quiz Tendency for a material to oppose the flow of electrons
What 3 quantities are related to Ohm’s Law Resistance Voltage, current, and resistance

Review Quiz of 20.2 before next section
View here

20.3 20.3 Electric Circuits

Circuit is a closed path through which electrons can flow.

Circuit Symbols

Series Circuit Christmas lights are often wired this way.
Disadvantage – when 1 light goes out the whole strand goes out.

Series Circuit

Parallel Circuit Electricity has several paths that it can travel.
Used in households. When one circuit is closed others still work.

Parallel Circuit

Series or Parallel? Parallel

Series or Parallel? Series

Power = current x voltage
Electrical Power Expressed in watts (W) or kilowatts (kW) The amount of power an appliance used can be calculated by Power = current x voltage Watts = amps x volts P = I x V

Power is expressed here as E for “energy”

Mini Quiz A _____ is a closed path in which electrons flow Circuit
Christmas lights are an example of ….. Household wiring are wired by … Circuit Series Circuit Parallel Circuits

Number your paper 1-9. View here
Video quiz Number your paper 1-9. View here