Unit D: Electrical Principles

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Unit D: Electrical Principles. Topic 1: Transfer and Storage of Electrical Energy. I. Review. What is electricity?. Is the energy of charged particles. Is when electrons are moved. Remember: Electrons are the outer particle of an atom. I. Review.

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### Unit D: Electrical Principles

Topic 1: Transfer and Storage of Electrical Energy

I. Review
• What is electricity?
• Is the energy of charged particles
• Is when electrons are moved

Remember: Electrons are the outer particle of an atom

I. Review
• All matter is made of particles; Particles are atoms
• Atoms are made of 3 sub-atomic particles:
• Neutrons – neutral (0) particles
• Protons – positive (+) particles
• Electrons – negative (-) particles
I. Review
• Draw an atom!
I. Review
• Atoms are neutral – this means :

# of protons = # of electrons

• Being charged means having unequal protons and neutrons
• +++ - - - -
• + - +- -
• - - - - -++
• Easiest method of charging, is through friction!!!
II. Static electricity

A. Laws of Electrical Charge

• Opposite charges attract

(+ and – will attract)

• Like charges repel (ex. + and + will repel)
Activity: Charge It

To witness the action of uncharged/ charged objects on each other.

 Remove charges from objects by running through your hand

 Charge objects by running through paper towel or fur

I. Static electricity
• Definition: The state of having unequal number of protons and electrons ; is an UNMOVING charge
• “static” means not moving;
• charge DOES NOT flow constantly

(vs. current electricity where charges are flowing)

I. Static electricity

A. Charge Separation

• Occurs when a charged object is brought close to a neutral object
• The same charges will repel, causing the opposite charges to attract
B. Electrical Discharge
• Although static electricity does not move, it is “discharged”
• Is the process of built up electrons transferring to other objects (Shocked!) Ex. lightning

Electric eel

Simulation

B. Electrical Discharge
• Discharging makes the charges between objects equal
• [Draw objects : Before / After ]
B. Electrical Discharge
• Grounding – a method of discharging an object
• Done by connecting object with a wire to the Earth (it can absorb lots of electrons)
C. Van DerGraff Generators
• Used to study electrical discharges
• Electrons build up on the outside sphere through friction -> the electrons seek to be discharged
What is the difference between current electricity and static electricity?
• Current electricity is a flow of electrons
• Static electricity is a build-up of charges (+ or -)
A. Circuit
• Is a path of electron flow
• Usually includes:
• source (battery)
• conductor (wire)
• switch (opens or closes a circuit)
• Must be complete /closed for electricity to flow
Sidenote:
• Microcircuits –small circuits with low voltage and current.

Where have you seen these parts before?

Circuit symbols:

wire

lamp

switch

resistor

- +

Cell (battery)

A. Circuits
• Schematic diagrams – a neat representation of a circuit using circuit symbols
B. Terms of Current Electricity
• Conductors– materials which allow the flow of electrons (ex. Metals, water)
• Insulators – materials which prevent (resist) the flow of electrons (ex. Plastic)
• Load – a device which converts electrical energy to other forms of energy
B. Terms of Current Electricity
• Examples:

1. What is the difference between 1.0A and 3.0A?

2. What is the difference between 1.5V and 9.0V?

3. What is the difference between 2.0 and 6.0 ?

Video
• How could the following picture be a metaphor for:
• current
• voltage
• resistance
B. Modeling Electricity

Ex. Waterfalls

Current – how quickly the water is flowing down the waterfall

Resistance – how many rocks are in the stream bed, preventing the flow of water

Voltage – the height of the waterfall (how much energy the water has)

C. Cells and Batteries
• Cells and batteries create current electricity in a circuit

>Create the electron flow

C. Cells and Batteries

I. Basic Terms

• Electrochemical Cell – a device that transforms chemical energy into electrical energy
• Ex. AA, AAA – all 1.5V “batteries” are actually cells
I. Basic Terms
• Batteries –multiple cells joined together to create a larger voltage
ACTIVITY: Cell Vs. Battery
• Predict the voltage of each of the following:

Remember: 1 cell = 1.5V

I. Basic Terms

Dry cells – when the electrolyte is a paste

Wet cells- when the electrolyte is a solution

I. Basic Terms

Primary cells – cells that cannot be recharged

Ex. Manganese-oxide alkaline batteries

Secondary cells – cells that can be recharged by using electrical energy to reverse the chemical reaction

• “rechargables”

Ex. Car batteries, cell phones, Ni-Cd batteries

- will wear out over time

II. Parts of an electrochemical cell
• 1 or 2 Electrolytes – a solution or paste that conducts electrolytes (ions)
• 2 Electrodes – metals/ solids conductors (allow movement of e-)
• Cathode is positive (receives electrons)
• Anode is negative (gives away “Source” of electrons)

III. How A Cell Works

1. Electrons are transferred from the negative electrode through a wire – head to the load

(+)

(-)

III. How A Cell Works

2. Ions (Ex. Cu2+(aq)) from the electrode are transferred through the solution (electrolyte) to the positive electrode.

3. The anode eventually is

“eaten away” or used up

(+)

(-)

Draw a Cell in Action!Draw a cell with the following parts: -copper electrode, copper solution -nickel electrode, nickel solution -wire -bulb -2 beakers

Cell Lab: Evaluating Cell Design
• Summarize the following:
• What affect does decreasing the concentration of an electrolyte have on the voltage of a cell?
• What affect does using the same electrodes have on the voltage of a cell?
• What affect does using different combinations of electrolytes have on the voltage of a cell?
IV. Applications of Cells and Batteries
• We can apply batteries in useful ways:

Electrochemistry – the study of chemical reactions to produce electricity

• Electrolysis – using a battery (electricity) to split a compound into its elements

Ex. H20 -->

IV. Applications of Cells and Batteries

2) Electroplating – coating a metal with a thin layer of a wanted metal

• The object to be plated is connected to the (-) negative electrode of the battery

Ex. Plating inexpensive jewelry with gold

IV. Applications of Cells and Batteries

3) Galvanizing–coating parts with a layer of aluminum oxide (is much harder than aluminum)

Ex. Jewellery, screen doors, kitchenware

IV. Applications of Cells and Batteries

4) Electrorefining–removing impurities from metals

-impure metals are placed at (+) electrode and a pure metal is placed at (-) terminal.