Unit 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
SF pp.294,296,297
SIA pp.81,319-321 / identify, describe and interpret examples of mechanical, chemical, thermal (heat) and electrical energy
There are two main types of energy: kinetic and potential. Kinetic energy is the energy of motion. Any object or particle that is moving has kinetic energy. Potential energy is stored energy. Any object or particle that has energy but is not using it has potential energy. The unit of energy is the Joule (J).
·  mechanical energy- the combined total of kinetic and potential energies of an object or particle
·  chemical energy- a type of potential energy; the energy stored in the bonds of molecules
·  thermal energy- a type of kinetic energy; the energy of vibrating particles in a material
·  electrical energy- a type of potential energy; the energy carried by charged particles
SF pp.293,294,296,297
SIA pp.321-324 / 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. It converts electrical energy to mechanical energy.
·  A generator is a device that produces electricity. It converts mechanical energy to electrical energy.
·  A thermocouple is a device that produces electricity. It converts thermal energy to electrical energy.
·  A cell / battery is a device that produces electricity. It converts chemical energy to electrical energy.
A team of students constructed a solar powered car for their science fair project. The car was made by hooking up the car assembly to a motor and a solar panel. During the initial test-drive, the car traveled across the length of a well-lit room.
This car converted:
a. solar energy into mechanical energy into electrical energy
b. solar energy into potential energy into wind energy
c. solar energy into electrical energy into mechanical energy
d. solar energy into thermal energy into chemical energy
SF pp.301-308
SIA pp.288-292 / 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.
Dry cell- a device that converts chemical energy to electrical energy. They consist of two electrodes (two different pieces of metal) and 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 a paste.
Wet cell- Same as above, but the electrolyte is a liquid that is usually an acid.

Dry cells and wet cells. Figures 1.20 and 1.21 Science in Action 9
Dry cells and wet cells are both examples of primary cells. The reaction cannot be reversed, and as a result, the cells can only be used once.
Rechargeable cells are known as secondary cells. Two examples of rechargeable cells are Ni-Cd and Nickel metal-hydride.
Jack made a list of facts about a typical electrochemical cell.
Fact A: cell converts electrical energy to chemical energy
Fact B: cell consists of 2 different metal electrodes and an electrolyte
Fact C: a D cell, like the ones used in flashlights, is classified as a wet cell
Fact D: a cell with copper and zinc has good electrodes
If the statement is true, place a 1 in the corresponding blank. If it false, place a 2.
______
A B C D
SF pp.314
SIA pp.325 / 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
By winding current-carrying wire into a coil and wrapping it around an iron core, you can make an electromagnet. An electromagnet will move to line up with the magnetic field of a nearby permanent magnet. To keep the electromagnet spinning, motors use a commutator (split ring) and brushes. The commutator breaks the connection of the coil and thus the magnetic force. The armature continues to spin because of momentum. The commutator then reconnects!

Figure 3.17 Science in Action 9
Electric generators
A generator works in reverse. Instead of pumping an electric current into the armature and the armature turning as a result, you turn the armature and current is generated as a result.
SF pp.317
SIA pp. / 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 armature
b)  increasing the current increases the speed of the armature
c)  increasing the number of coils of wire between the magnets increases the speed of the armature
d)  changing the orientation of the magnets so that like poles are against each other will stop the armature
Jose has produced an electric motor for his science class. He wants to make the motor spin faster without using more voltage. He can do this by:
a. increasing the number of turns of wire
b. decreasing the strength of the fixed side magnets
c. making more splits in the commutator
d. changing to a power supply with more electrical output
2.  Describe technologies for transfer and control of electrical energy
SF pp.330-331
SIA pp.284-288 / 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
The voltage is the energy of individual charges. Ultimately it is the total energy that provides the danger, so a high voltage does not present a significant danger if there are not a lot of charges (low current). It becomes dangerous when the current (number of charges per second) is also increased to a high level, providing more overall energy.
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.
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
SF pp.266-268
SIA pp.274-278 / distinguish between static and current electricity, and identify example evidence of each
Static electricity- the build-up of electric charges (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- the flow of electric charges; the more charges that flow per
second, the higher the current. In general, electrical current
carries electrical potential energy which is used to operate
electrical devices
e.g. electrical energy carrying charges flow through a light
bulb; the electrical energy from the charges is converted to
light and heat
Two balloons became charged by rubbing them with different cloth materials.
What happens if Balloon A and Balloon B are brought near to each other?
a. Balloon A will attract Balloon B
b. Balloon A will repel Balloon B
c. Balloon A will have to effect on Balloon B
d. Balloon A will fuse with Balloon B
SF pp.269
SIA pp.298 / 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)
Electrical conductor- a material that allows charges to flow through it; some
materials are better conductors that 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.
Eg. Mercury at absolute zero.
Resistance-the property of something that hinders the motion of electric charge
and converts electric energy into other forms of energy such as light,
heat, and sound. The symbol for resistance is the letter R and the units
are Ohms (W).
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;
insulators offer 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
Michelle constructed a circuit in her science class.
Different objects were tested to determine whether they would complete the circuit to make the bulb light. The objects tested were:
i. a glass rod
ii. aluminum foil
iii. a paper clip
iv. a plastic spoon
Michelle concluded that the bulb will light for:
a. i and ii
b. i and iv
c. ii and iii
d. ii and iv
SF pp.273,283
SIA pp.298-302 / 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; something that resists the flow of electric
charge and takes electrical potential energy from charges and converts
it to some other type of energy, such as light, heat, sound, etc.
rheostat- a resistor whose resistance value can be changed. 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)
Mary and Sam created a motorized windmill for their science class using a series circuit. However, they found that their windmill moved too fast! They could adjust the speed of the windmill by:
a. adding another battery to the circuit
b. creating a parallel circuit
c. adding a light bulb to the circuit
d. removing the switch from the circuit
SF pp.278
SIA pp.304-305 / 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).
Jason and Celine used a sports cartoon to show how current, resistance, and voltage are related.

From this model, it can be concluded that X, Y and Z represent
a. current, voltage and resistance
b. voltage, resistance and current
c. voltage, current and resistance
d. current, resistance and voltage
SF pp.281-282
SIA pp.306-307 / 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.]
Amperage- a measurement of the strength of electric current. The symbol for
amperage is the letter I and the units are Amps (A). Amperage is
measured with an ammeter. Smaller currents are measured with
galvanometers.
Ohm’s law provides for the relationship between voltage across a resistor (the energy that each charge loses across the resistor), the current through the resistor (the amount of charges that are flowing through the resistor each second), and the resistance of the resistor. Ohm’s law can be written as a mathematical equation:

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=22 A V=220 V
Find: R = ?