Science 9 Study GuideUnit D: Electrical Principles and Technologies

STS and Knowledge:1. Investigate and interpret the use of devices to convert various forms of energy to electrical energy, and

electrical energy to other forms of energy

1. Identify, describe and interpret examples of mechanical, chemical, thermal (heat) and electrical energy Energy is measured in Joules (J).

Kinetic energy – the energy of motion thermal energy- the energy of vibrating particles in a material

Potential energy – stored energy. chemical energy- the energy stored in the bonds of molecules electrical energy- energy carried by charged particles

Mechanical energy- kinetic and potential energies of an object.

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Science 9 Study Guide2. Investigate and describe evidence of energy transfer and transformation (e.g.,mechanical energy

transformed into electrical energy, electrical energy transferred through power grids, chemical energy converted to electrical energy and then to light energy in a flashlight, thermal energy converted to electrical energy in a thermocouple)

An electric motor is a device that used to turn something. Electrical → Mechanical. A generator is a device that produces electricity. Mechanical → Electrical. A thermocouple is a device that produces electricity. Thermal → Electrical A cell / battery is a device that produces electricity. Chemical → Electrical.

3. investigate and evaluate the use of different chemicals, chemical concentrations and designs for electrical storage cells (e.g., build and test different forms of wet cells)

Electrochemical cell: a package of chemicals designed to produce small amounts of electricity e.g. a battery.

Wet cell - a device that converts chemical energy to electrical energy. - They consist of two electrodes (two different pieces of metal) - an electrolyte (a conducting solution). - Charges leave the negative electrode, pass through the electrolyte, and return to the positive electrode. - They are called dry cells because the electrolyte is in the form of an ionic liquid (usually acid)

Dry cell - Same as above, but the electrolyte is a conductive paste.

Dry cells and wet cells. Figures 1.20 and 1.21 Science in Action 9

Primary Cells:- The reaction cannot be reversed, and as a result, the cells can only be used once.- Dry cells and wet cells Secondary Cells:- The reaction is reversible. This means these cells can be recharged- Two examples of rechargeable cells are Ni-Cd and Nickel metal-hydride.

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Science 9 Study Guide4. construct, use and evaluate devices for transforming mechanical energy into electrical energy and\for

transforming electrical energy into mechanical energy

Figure 3.10 Science in Action 9

Electric motors- Moving current creates a magnetic field

- If that current wraps around an iron core the magnetic field is amplified and we get an ELECTROMAGNET.- Electromagnets are temporary magnets

- The armature carries the current and becomes an electromagnet.

- When the armature is placed near a permanent magnet it will spin to align with the magnetic field.

- A motor uses this movement.

- The commutator (split ring) attached to the armature breaks the circuit and allows the electromagnet to keep spinning (momentum) rather than stopping once it is aligned.

- The commutator then reconnects and recreates the electromagnet!

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Java Applet: Rotation of Motors with/without a commutator

http://www.sciencejoywagon.com/physicszone/otherpub/wfendt/generatorengl.htm

Science 9 Study Guide

Figure 3.17 Science in Action 9

Electric generators- A generator works in reverse. - The armature is forced to turn inside a magnetic field which creates an electric current

5. modify the design of an electrical device, and observe and evaluate resulting changes (e.g.,investigate the effect of changes in the orientation and placement of magnets, commutator and armature in a St. Louis motor or in a personally-built model of a motor)

Several ways to change the speed at which the armature in a motor spins:a) increasing the strength of the magnets increases the speed of the armatureb) increasing the current increases the speed of the armaturec) increasing the number of coils of wire between the magnets increases the speed of the armatured) changing the orientation of the magnets so that like poles are against each other will stop the armature

2. Describe technologies for transfer and control of electrical energy1. assess the potential danger of electrical devices, by referring to the voltage and current rating

(amperage) of the devices; and distinguish between safe and unsafe activities- Voltage: The energy of individual charges. - Amperage: the NUMBER of charges

- Consider water falling on your head. - The higher it falls from the more energy it has (but 1 or 2 drops won’t really hurt)- If a bathtub of water fell on our head though, even from not very high up that could hurt a lot).

- Voltage is the energy (“height”) of your electrons. Amperage is the number (“weight”).

- You can survive a high voltage zap if there isn’t much of it running through you. But a large amount of current at even low energy could be fatal.

- To assess the danger of an electrical device, check the manufacturer’s label for voltage and current rating. Remember that it is the combination of high voltage and high current that provides the danger.

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Science 9 Study Guide

Some electrical safety pointers*: Never handle electrical devices when you are wet or near water unless they are specially designed and approved

for use in wet areas. Don’t use any power cord that is frayed or broken. Always unplug electrical devices before looking inside or servicing them. Don’t put anything into an electrical outlet other than proper plugs for electrical devices. Don’t overload circuits by plugging in and operating too many devices. Stay away from power lines. Don’t bypass safety features built into home wiring, appliances, and other electrical devices. When unplugging a device, pull on the plug, not on the electrical cord. Never remove the third prong from a three-prong plug.*Science in Action 9 (Addison Wesley) p.285

2. distinguish between static and current electricity, and identify example evidence of each

Static electricity:- The build-up and separation of electric charges on an object. (protons and electrons are not equal!).- Charged objects cause charge separation when they are brought close to neutral objects.

e.g. the build-up of charges in your hair when you put a wool sweater on; these charges are transferred from the wool to your hair e.g. lightening results from a build-up of charges in clouds; when the build-up becomes to large, the charges jump (discharge) to the ground

Current electricity (moving)- The flow of electric charges.- The potential energy in each charge is the voltage. More potential energy means higher voltage.- The number of charges that flow is the current. More charges flowing per second means higher current.

e.g. Imagine someone is standing on the topic of the Calgary tower with an eye dropper full of water. They release 1 drop of water every second. The energy of each drop is determined by the height of the tower. If this drop where to land on your head it would not likely cause that much harm, even though it is falling with high energy. However, If this persona changes from dropping 1 drop/sec to a bathtub full of water every second (millions of drops/sec) then even though each molecule of water still has the SAME amount of energy, the sheer volume of water could cause severe damange.

3. identify electrical conductors and insulators, and compare the resistance of different materials to electric flow (e.g., compare the resistance of copper wire and nickel chromium/Nichrome wire; investigate the conduction of electricity through different solutions; investigate applications of electrical resistance in polygraph or lie detector tests)

Almost everything can conduct electricity to some degree.

Electrical conductors- Allow charges to flow through it easily;- Some materials are better conductors than others in that they allow charges to flow easier

- e.g. most metals are good conductors; copper is a very good conductor and is used to carry charges through your house, while nichrome metal conducts charges but not as well.

Superconductor- Have almost no resistance to electron flow (very very good conductors).

- Eg. Mercury at absolute zero.

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Science 9 Study GuideResistance- Slows the motion of electric charges (current)

- This slowing forces the electric energy to convert into other forms of energy such as light, heat, and sound. - The symbol for resistance is the letter R and the units are Ohms ().- e.g. the filament in a light bulb generates heat because of resistance- e.g distilled water is a resistor- e.g. lie detectors – measures skin resistance because sweat is a salty and conductive solution

Electrical insulator- A material that does not allow charges to flow through it(or it flows incredibly slowly);- Insulators have HIGH resistance to the flow of electric charge. - If something is a good insulator, it is a poor conductor.

- e.g. rubber and plastic are good insulators

4. use switches and resistors to control electrical flow, and predict the effects of these and other devices in given applications (e.g., investigate and describe the operation of a rheostat)

switch- something that will start or stop electric current

resistor- something that has resistance; reduces electrical potential energy for each charge and converts it to another type such as light, heat, sound, etc.

rheostat- a resistor with variable resistance (like a dimmer switch). Since nichrome wire has a relatively high resistance, adding more nichrome to a circuit will increase the overall resistance. Taking nichrome away will decrease the overall resistance. (aka variable resistor)

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Science 9 Study Guide

5. describe, using models, the nature of electrical current; and explain the relationship among current, resistance and voltage (e.g., use a hydro-flow model to explain current, resistance and voltage)

voltage- the energy of each individual charge. The symbol for voltage is the letter V and the units are Volts (V). Volts are measured with a voltmeter.

Pretend an electric circuit is a race track. Each car represents a charge. Each car has a certain amount of gasoline that provides its energy. The gasoline that each car has would represent the voltage. The number of cars that pass by the starting line every second would represent the current. As cars (charges) go up hills (resistors), each one of them uses up gasoline (voltage). Each car needs to get more gasoline (voltage) at the pit stop (battery).

Imagine a water pump. The pump raises the water up and gives it potential energy (voltage). As the water falls it loses energy. If a turbine is in the path of the water, the falling water will lose even more energy as it turns the turbine (the resistor). The volume of water would be the current of the circuit

6. measure voltages and amperages in circuits, and calculate resistance using Ohm’s law (e.g., determine the resistance in a circuit with a dry cell and miniature light; determine the resistances of copper, nickel-chromium/Nichrome wire, pencil leads and salt solution) [Note: At this level, students are not required to use Ohm’s law to calculate current flow.]

Voltage:- The potential energy of each charge. Units are Volts (V).- The symbol for amperage is the letter V- Measured with an voltmeter

Amperage:- The strength of electric current. The number of charges flowing per second- Units are Amps (A) - The symbol for amperage is the letter I - Measured with an ammeter.- Smaller currents are measured with galvanometers.

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High Voltage

Resistor

Low Voltage

Battery

Science 9 Study GuideResistance:- The strength of the resistor.- Units are Ohms (Ω) - The symbol for amperage is the letter R - Measured with an Ohmmeter- Smaller currents are measured with galvanometers.

Ohm’s law- Relates Voltage, Amperage and Resistance

V=IR

e.g. An electric dryer draws an electric current of 22 A. The voltage drawn by the dryer is 220 V. What is the resistance of the dryer?

Given: I = 22A V =220VFind: R = ? V=IR

R=VI

R=220 V22 A

R=10Ω

7. develop, test and troubleshoot circuit designs for a variety of specific purposes, based on low voltage circuits (e.g., develop and test a device that is activated by a photoelectric cell; develop a model hoist that will lift a load to a given level, then stop and release its load; test and evaluate the use of series and parallel circuits for wiring a set of lights)

Photoelectric cells:- Respond to light and create and electric charge which can enter a circuit and power devices

- The above burglar alarm uses a beam of UV light to power an electromagnet- This electromagnet keeps a second circuit open. - If the beam of light is broken, the electromagnet turns off and the second circuit closes sound an alarm.

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Science 9 Study Guide

8. investigate toys, models and household appliances; and draw circuit diagrams to show the flow of electricity through them (e.g., safely dismantle discarded devices, such as heating devices or motorized toys, and draw diagrams to show the loads, conductors and switching mechanisms)

An electrical circuit is a system made up of 4 subsystems:1. Source – cell or battery2. Conductor – wire3. Control – switch4. Load – lamp/motor

The following is a list of symbols used when drawing electric circuit diagrams (from Science in Action 9 (Addison-Wesley) p.312

Series circuits:- The current passes through each load in the circuit.- There is only one path for the current to pass through. - If any single load is removed, the circuit opens and the current stops

Figure 2.24 from Science in Action (Addison-Wesley) p.313

Parallel circuits:- The current has many possible pathways.- There is only one path for the current to pass through. - If any single load is removed, there are still other paths available for the current to keep moving.

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Science 9 Study GuideFigure 2.25 from Science in Action (Addisson-Wesley) p.313

9. identify similarities and differences between microelectronic circuits and circuits in a house (e.g., compare switches in a house with transistors in a microcircuit)

Microcircuits: - Similar to large household circuits - The primary difference is smaller circuits mean smaller voltages and amperagesHousehold circuits might have dozens of electrical component but a microelectronic circuit (integrated circuit), there may be millions of transistors and resistors operating on much smaller power.

3. Identify and estimate energy inputs and outputs for example devices and systems, and evaluate the efficiency of energy conversions.

1. identify the forms of energy inputs and outputs in a device or system

- Devices are basically energy transformations devices- lightbulb- the input energy is electrical, the output energy is light and heat.- cd player- the input energy is electrical, the output energy is sound (and also kinetic as the disc spins)- biking – the input energy is chemical, the output energy is mechanical/kinetic

2. apply appropriate units, measures and devices in determining and describing quantities of energy transformed by an electrical device (e.g., measure amperage and voltage, and calculate the number of watts consumed by an electrical device, using the formula P = IV [power (in watts) = current (in amps) voltage (in volts)]; calculate the quantity of electric energy, in joules, transformed by an electrical device, using the formula E = P t [energy (in joules) = power (in watts) time (in seconds)])

Power:- The rate at which a device converts energy.- The symbol is P- The units are Watts (W). - 1 Watt is equal to 1.0 J/s.

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Science 9 Study Guide

There are two equations that describe power relationships:

P=VI E=Pt

e.g. A 100 W light bulb is plugged into a 120 V outlet and is on for 5 minutes. a. What is the current? b. What the energy used?

Given: FindP = 100W I = ?V =120Vt=5 minutes=300 seconds

a. P=VI I= PV

=100 W120 V

=0.83 A The current is 0.83A

b. E=Pt=(100 W ) (5min )( 60 smin )=30000 J The energy used is 30kJ

3. apply the concepts of conservation of energy and efficiency to the analysis of energy devices (e.g., identify examples of energy dissipation in the form of heat, and describe the effect of these losses on useful energy output)

The law of conservation of energy:- Energy cannot be created or destroyed, only transformed from one type to another.

Efficiency - The percentage of original energy (input) that remains after an energy conversion (output). - No device is 100% efficient.- This does not mean that energy is destroyed; it was simply ‘lost’ to an unusable form such as heat.

- e.g. A light bulb uses electrical energy input to produce light. The conversion is not 100% efficient. Some of the energy was lost in the form of heat. Note that no energy was destroyed!!

- Eg. A car converts chemical energy (gas) to kinetic energy(motion). The heat and sound of a car is all part of the energy that is lost to the environment instead of being converted to motion

4. Compare energy inputs and outputs of a device, and calculate its efficiency (e.g., compare the number of joules of energy used with the number of joules of work produced, given information on electrical consumption and work output of a motor-driven device)

Efficiency:

% Efficiency=usefulenergyoutput

totalenergyinput

x 100 %

- eg. A light bulb uses 780 J of electric energy, but produces only 31 J of light energy. What is the efficiency of the light bulb?

Given: Find:Useful energy output=31 J % Efficiency= ?Total energy input=780 J

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Science 9 Study Guide

%Efficiency=usefulenergy outputtotal energy input

×100 %= 31 J780 J

×100%=3.9 %

investigate and describe techniques for reducing waste of energy in common household devices (e.g., by eliminating sources of friction in mechanical components, using more efficient forms of lighting, reducing overuse of appliances as in “overdrying” of clothes)

There are many ways to prevent energy loss (increase efficiency)- pick appliances that are energy efficient (they have energy labels on them)- don’t leave lights on when not in the room- use full loads of laundry and dishes- improve bearings and lubricants in devices to reduce friction- add more insulation around stoves, refrigerators, and walls

4. Describe and discuss the societal and environmental implications of the use of electrical energy.

1. identify and evaluate alternative sources of electrical energy, including oil, gas, coal, biomass, wind, waves and batteries (e.g., identify renewable and nonrenewable sources for generating electricity; evaluate the use of batteries as an alternative to internal combustion engines)

Renewable source- a source of energy that can replenished naturally in a relatively short period of time

Examples of renewable sources: Tides- moving water from tides turn turbines that run generators There are not a lot of tidal power stations in the world because of the difficulty in finding a suitable location. They are, however, an environmentally friendly source of energy. Hydro-electric plants like those near Niagra Falls, capture the energy of falling water.

Wind- use the wind to turn a turbine that run generators Modern windmills are more efficient than older ones because of the

propeller shaped blades. They are not particularly efficient, but are

environmentally friendly. They are usually grouped together in wind

farms, such those in Pincher Creek.

Sunlight- uses the Sun to generate electricity Recall that when a photoelectric cell can emit electrons when exposed to light. Sunlight can be used to generate electricity in this way. Modern silicon materials have made sunlight a more efficient way of producing current. Solar cells are now used in many applications, including calculators and spacecraft and the International Space Station. This source of electricity is very environmentally friendly.

Batteries – Convenient source of electricity for portable devices, but they only produce energy after being charged using electricity from an external source. They actually use more energy than they produce!

Non-renewable source- a source of energy that cannot be replenished naturally in a relatively short period of time.

Fossil fuels- coal, oil, and natural gas.

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Science 9 Study Guide Fossil fuels are a reasonable choice in areas that have a large deposit that is easy to excavate. Mining coal or tapping into deposits of oil and natural gas is only the first step in refining fossil fuels in order to generate electricity from fossil fuels. This non-renewable source of electricity is not environmentally friendly.

2. describe the by-products of electrical generation and their impacts on the environment (e.g., identify by-products and potential impacts of coal-fired electricity generation)

Air pollution from burning fossil fuels:

Fly ash: When coal is burned fly ash is released into the air. Fly ash contains mercury, a poisonous metal that can damage the nervous system.sulfur dioxide- has been identified as causing acid rainnitrogen oxides- major cause of air pollution and acid raincarbon dioxide- has been identified as causing global warning

Strip-mining:Strip-mining is used when deposits are near the surface. Coal is often mined using this method, and the coal can be used to generate electricity. This type of mining removes all plants and animals from the area. The natural environment is never fully restored.

Oil and gas fired generators:Oil or gas is burned to heat water, which becomes steam and turns a turbine to generate electricity. This process releases poisonous gases and warm water into nearby lakes and rivers. There is a need to monitor plants and animals in the area to ensure their health.

Oil is pumped from wells, sometimes by injecting water into the ground. A significant amount of fresh water goes into the ground, out of the water cycle forever. Natural gas wells produce sour gas which is poisonous.

3. identify example uses of electrical technologies, and evaluate technologies in terms of benefits and impacts (e.g., identify benefits and issues related to the use of electrical technologies for storing and transmitting personal information)

Some technologies based on electricity:- Computers

- Make most tasks more efficient. Some calculations would take years without computers- more instant communication- Lots of waste produced when computers are discarded

- Lasers- Used in everything from medical procedures to cd players to dental work to communication- Very expensive

- Cell phones- Instant communication of all media types- a person is almost always reachable

In general, many people would argue that technology had made our lives easier. Some would argue, however, that we are experiencing an information overload and are working harder than ever as a result of technology.

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Science 9 Study Guide

4. identify concerns regarding conservation of energy resources, and evaluate means for improving the sustainability of energy use

Some concerns:- shrinking natural resource reserves- increasing demand on natural resources- environmental concerns with the means in which resources are obtained, used, and discarded (how are the rare

metals acquired?)

Some ways to improve the sustainability of energy use:- manage resources according to what we have rather than what we use- improve the efficiency of machines and appliances- use more renewable sources of energy, and avoid the use of non-renewable energy sources make good personal

choices

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