Energy Types & Transformations

Forms of Energy

Energy is the ability to do work, there are many different forms of energy!

  1. Chemical – energy stored in chemical bonds
  2. Electrical – energy of charged particles
  3. Mechanical – energy of moving objects
  4. Thermal – kinetic energy of particles (heat energy)

Chemical Energy

  • Energy is stored in chemical bonds
  • Energy is released or absorbed in chemical reactions
  • Chemical energy can be transformed into other forms of energy

Ex. electrical, mechanical, sound


Energy Transformations

you can use various devices to transform energy from one type to another

  • chemical energy to electrical energy

(ex) batteries, hydrogen cell

  • thermal energy to electrical energy

(ex) thermocouples

  • electrical energy to thermal energy

(ex) oven, space heater

  • electrical energy to chemical energy

(ex) battery charger


Energy Transformations Involving Electrical & Mechanical Energy

 PHYSICS GANG SIGNS

PHYSICS GANG SIGNS

Electric Motors

All electrical motors have 4 parts:

  1. Magnets along the outside
  2. Armature – rotating shaft of motor
  3. Commutator – broken ring that breaks and reverses the flow of current
  4. Brushes – conduct electricity from cell or battery to commutator
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how a motor works:

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  1. Electric current travels from the brushes into the commutators
  2. Commutators magnetize the wire coil
  3. Magnets push or pull the wire coil
  4. Rotation of armature switches the position of the commutators
  5. Cycle continues until current is stopped

 AC/DC

 THE FLOW OF ELECTRONS IN DIRECT CURRENT VS ALTERNATING CURRENT

THE FLOW OF ELECTRONS IN DIRECT CURRENT VS ALTERNATING CURRENT

Direct and Alternating Current

Direct current (DC):

Current of electrons flow in only one direction (from negative to postive terminal in a battery) 

  • Used in devices such as calculators, watches, cell phones, MP3 players etc 

Alternating current (AC):

Current of electrons flow back and forth 60 times per second  

  • Used in household circuits
  • Plug-in devices that require DC current come with their own power supply that converts the socket’s AC current into DC and then supplies the voltage required (Called a transformer) 

Transformers

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  • The most efficient way to transmit current over long distances is at a high voltage (500 000 V)
  • However we can’t use this in our houses so the voltage needs to be dropped
  • Transformers use magnetic fields to transform one voltage to another

There are two types of transformers:

  1. Step down transformer – reduces voltage - have less coils coming out than going in 
  2. Step up transformer – increases voltage - have more coils coming out than going in

Generators

Electromagnetic induction is the generation of electrical current by moving a conducting wire through a magnetic field

  • used for large scale generating plants
  • massive coils of wire rotate around a magnetic field in huge generators to produce electricity
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There are two types of generators:

  1. DC – like a DC motor where the spinning armature produces a one way flow of electrical current
  2. AC – has 2 slip rings instead of a commutator, current flows out through one slip ring then the other, alternating

Build a series circuit with AC current, with the following:

  • A switch
  • Two lightbulbs
  • A voltmeter
  • A ammeter

Also build a parallel circuit with AC current, with the following:

  • A switch
  • Two lightbulbs on their own parallel line
  • A voltmeter
  • A ammeter

REVIEW QUESTIONS


Measuring Energy Input & Output

Power:

Power is the rate at which a device converts energy, measured in watts (W)

P = IV

where:  P = power in watts (W)

                  I = current in Amperes (A)

             V = voltage in volts (V)

Example

Calculate the power used by an MP3 player if it uses a current of 5.0 A and a voltage of 3.0 volts.

I = 5.0 A              P = IV

V = 3.0 V                 = (5.0 A)(3.0 V)

P = ?                        = 15 W

REVIEW QUESTIONS


Energy:

The power rating of a device and the time it runs to calculate the amount of energy used, measured in Joules (J)

E = Pt

where:       P = power in watts (W)

                 t = time in seconds (s)

                  E = energy in Joules (J)

Example

Calculate the energy usage if a 15 W MP3 player operates for 2 minutes.

P = 15 W                               E = Pt

T = 2 min                                  = (15 W)(120 s)

   = 2 min x (60s/min)            = 1800 J

   = 120 s                                  

E = ?

REVIEW QUESTIONS


 The Kilowatt Hour

In our households, it doesn’t take long to use up a lot of Joules of energy!

  • Because we use a lot of energy we use a more practical unit called the kilowatt hour

Calculated with the same formula   E = Pt

But, in this case...

  • Power is measured in kilowatts (1 kW= 1000 W)

  • time is measured in hours (h)


Energy Dissipation

Law of Conservation of Energy:

Energy cannot be created or destroyed, it can only change from one form to another

With electricity energy is "lost" (dissipated) as heat, sound and/or light in every conversion


Efficiency

The efficiency of a device is a comparison of the input energy and useful output energy

Efficiency =  Joules of useful output / Joules of input energy

or restated as:

Eff =  Work Output (J) / Work Input (J)

Efficiency percentage  = Eff x 100

 

                              

Example

Calculate the efficiency of a light bulb that emits 20 J of light energy for every 80 J of input energy.

Work Input = 80 J

Work Output = 20 J

Efficiency = ?

Eff = Work output (J) / Work input (J)                                  

     = 20 J/ 80J   

     = 0.25

Efficiency (percentage) = Eff x 100

                                       = 0.25 x 100

                                       = 25 %


 Reducing the Energy Wasted by Devices

There's a limit to Efficiency

  • Devices used for heat are very efficient (ex a space heater)
  • Any device that does not use the heat produced in the energy transformation is not as efficient (ex a light bulb) 

Efficiency can be increased by:

  1. Decrease friction in the system – can use bearings and oils with moving parts (motor oil in an engine) 
  2. Increase insulation – improve for devices that you don’t want to lose heat from (ex refrigerator, or oven)

 


Electrical Energy Sources & Alternatives

How we generate electricity

1. Start with the boom! Release energy as heat!

  • About 65% of the electricity in the world is generated by burning oil, coal or natural gas
  • In Alberta most of our energy comes from burning coal, however we are shifting to renewables 
  • Can also use nuclear fission, in which a heavy element like uranium is split into smaller atoms

2. Use heat to turn water into steam

  • Steam then turns large turbines
  • Each turbine rotates wire coils in a generator which produces electricity

3. Allow water to cool down, and reuse water/ release water

**can also get energy to turn water into steam from geothermal energy or burning biomass ,with hydro-electric power, the energy of the falling water turns the turbines


Alternative Energy Sources

1.  Tides

Moving water can power turbines that run generators

(ex)  Nova Scotia in the Bay of Fundy

2.  Wind

Moving air (wind) can turn turbines that run generators

(ex) in Pincher Creek Alberta

3.  Sunlight

Solar energy is converted into electrical energy by silicon-based solar cells

4. Hydro Electric Dams

Moving flowing down a grade powers turbines that run generators

5.  Fuel Cells

Chemicals continuously feed a chemical reaction that produces electricity

(ex)  hydrogen gas  +  oxygen gas  into  water  +  electricity


Renewable vs. Nonrenewable Resources

Renewable resources:

Resources that can be replaced in a short period of time

(ex) solar energy, wind energy

Nonrenewable resources:

Resources that cannot be replaced as they are used up

(ex) fossil fuels, uranium

WINDMILL POWER


Electricity & the Environment

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Air Pollution

  • Burning fossil fuels releases pollutants
  • Coal-burning power plants release small amounts of fly ash into the atmosphere which contains mercury
  • SOx, NOx, and CO2 released through combustion lead to acid rain formation
  • CO2 also causes the enhanced greenhouse effect

Other Environmental Effects

  • strip mining of coal results in a disruption of the environment
  • oil and gas wells may release deadly gases
  • steam turbines release warm water into rivers and lakes, which can harm organisms
  • nuclear reactors produce radioactive wastes
  • hydroelectric dams flood river valleys
  • wind farms make large areas of land not useable for anything else
  • building solar cells requires harmful chemicals
  • tidal generators displace marine organisms
  • “green” sources of energy (tidal, geothermal, wind) harm the environment much less than burning fossil fuels

Conservation

  • higher demand for energy means higher consumption of energy resources
  • lowering energy use conserves nonrenewable resources
  • conserving energy means using resources at a rate that can be maintained indefinitely
  • called sustainability
  • personal decisions by all people influence sustainability

Electrical Technology & Society

Benefits

  • improved standard of living
  • can complete tasks faster, giving us more free time

Disadvantages

  • technology can be expensive
  • sustainability is threatened
  • old discarded technologies adds to solid waste

Computers

  • computers use binary numbers (one’s and zero’s)
  • different technologies store and transmit computer information

(ex) CD’s, hard drives, microcircuits

  • “hackers” can break into computer systems
  • “viruses” exist and slow down computers
  • internet has lots of information…not always correct
  • can get “information overload” from the amount of material that is available through computers

Viewpoints

You can look at how things affect society through a variety of viewpoints:

1.    economical – money

2.    political – laws and governments

3.    technological – technology

4.    environmental – effect on ecosystems, organisms etc