administration student task rubric student work technical quality
Electrical Energy
Contributed by: Council of Chief State School Officers (CCSSO/SCASS)

Item Description:
One of the variables which change in this event is the gauge numbers which correspond to the different wire diameters. As the gauge numbers increase the wire size or diameter decreases. As the gauge number decrease the wire size or diameter increases. So a 32- gauge wire has a larger diameter than a 36-gauge wire. The diameter and cross-sectional area then affects the wire's ability to conduct or restrict current and heat. Criterion (A) looks at the student's understanding of gauge number. Criterion (A1) is for the student who recognized that the 36-gauge copper wire has the smallest diameter of the four. Criterion (A2) covers just the opposite by addressing the fact that any of the other wires are 32-gauge and have a larger diameter. As far as the large diameter wires having less resistance to current and in turn poorer conductors of heat. The student does not have to be specific here to get on point. Criterion (A3) clarifies this.

Criterion (B) looks at a student's understanding of how copper, steel, and nichrome, affect the resistance and conductivity or current and heat differently. Each type of material has a particular resistivity rating. Criterion (B1) and (B2) give a student credit for recognizing and describing the fact that nichrome is a material that has a high resistivity to current and conducts heat fast or that steel has a low resistivity to current and conducts heat fast or that steel has a low resistivity to current and conducts heat slow. Copper falls in between although the student must reference its resistivity or conductivity somehow. Criterion (B3), gives credit to the student who just mentions the fact that a wire's mass or density affect how well a wire conducts current or heat.

While gauge and type describe two things there are several other physical characteristics which tell a student heat energy is being produced. When a student describes how a wire must be giving off more heat the redder or brighter it gets, they have addressed criterion (C1). In a more general sense, if a student describes that the wire gave up more heat because they could feel it or see it cut down through the crayon faster, they have addressed Criterion (C2) or C3).

Criterion (D), looks at whether or not the student can suggest the best wire type to use to fix a broken space heater, in question two. For Criterion (D1), to student has to simply choose a wire type and justify why it would be best choice. Their reasoning has to agree with that given to question one or supported by their data on page 5. Some students may describe a way to fix the space heater that calls for an alteration that changes the density, diameter, length, or temperature of the wire used. For instance a student might suggest doubling up a wire so that it would produce more heat. Criterion (D2) gives credit here.

Note: Throughout this even many students will find little if any difference in the 36- gauge copper wire and the 32-gauge nichrome wire. The four Criterion have been set up with this in mind and does not penalize the student who does not discover that the 32- gauge nichrome wire realistically is the better conductor (radiator), of heat.

Main Concepts:

1)  The heat generated when current passes through a resistive material is used in many common devices. This conduction of heat is the result of molecular collisions. Collisions are affected by the cross-sectional area, length, and type of material of the conducting path, (the temperature of the room also has its affects.) The resistance of a current-carrying wire is directly proportional to its length and inversely proportional to the cross-sectional area. Resistance increases with an increase in length in and it decreases with an increase in cross-sectional area. Gauge numbers are given to the different wire types and diameter. 32 gauge wire is smaller in diameter than 16 gauge. The resistance of a thick wire would be less than that of a thin one since a thicker wire has more are for the electrons to pass through. Resistance increases with the length of the wire because there would be more obstacles to obstruct electron flow. So, for certain devices which do produce heat as their main function, such as electric space heater, us narrow, long, copper or nichromium wires to conduct the most heat.

2)  Materials which have very high resistivity (low conductivity), are called insulators. The resistivities of various materials can be found in books. Copper is a popular metal of which wires are made. Its resistivity is 1.7 x 10-8 W x m (20 C). Depending on the diameter of the wire, copper is a fairly good electrical conductor favored by its inexpensiveness to produce. But, if a high voltage forces current through a narrow 36- gauge copper wire, it will heat up considerably. Nichrome (alloy of Ni, Fe, Cr), with a resistivity of 150 x 10-8 W x m (20 C), is not as good of a conductor as copper and in turn is a popular heating agent in a toaster or hair dryer. While other materials like glass and quartz have even higher resistivities to current flow, it becomes too expensive, not to mention difficult, to make wires with them.

3)  Wires exhibit several physical characteristics that show how well a wire conducts either electrical current or heat. This becomes quite obvious when various types of light bulbs are compared. The normal 60 watt bulb does not radiate as much heat as the 150 watt bulb that makes up a heat lamp. Careful observation of each bulb's filament will show that the heat lamp's filament glows with a much brighter yellowish red. One may also discover that the normal 60 watt light bulb will cool down much quicker than the heat lamp when they are shut down. The filament is usually just a small section of the whole electrical circuit made to conduct the heat and in turn light energy.

Scoring Rubric

Criterion A:
1)  [Q1 or Q2]  Student describes how the 36-gauge copper wire conducts the most heat or has the smallest diameter. or 2)  [Q1 or Q2]  Student describes how the 32-gauge copper, nichrome, or steel wires conduct less heat or that they have a larger diameter, than the 36-gauge copper. or 3)  [Q1 or Q2]  Student describes how as the gauge number increases, the wire diameter decreases or as the gauge number decreases, the wire diameter increases. or 4)  [Q1 or Q2]  Student describes how the conduction of heat increases as the gauge number increases or how the conduction of heat decreases as the gauge number decreases.

Criterion B:
1)  [Q1 or Q2]  Student describes how one wire conducts more heat than another because of the type of material (copper or nichrome), having a higher resistance to current flow. or 2)  [Q1 or Q2]  Student describes how one wire conducts less heat than another because of the type of material (copper or steel), having a lower resistance to current flow or does not conduct heat well. or 3)  [Q1 or Q2]  Student describes how the mass or density of a material affects the conductivity or resistivity of a wire.

Criterion C:
1)  [Q1 or Q2]  Student describes how a wire has radiating more heat as the redness of the wire or brightness in its light increased. or 2)  [Q1 or Q2]  Student describes how a wire that has more resistance to the flow of current will feel warmer or the wire that does not get as hot as others has less resistance to the flow of current. or 3)  [Q1 or Q2]  Student describes how a wire with a larger gauge number melts through the crayon faster than a wire with a smaller gauge number.

Criterion D:
1)  [Q2]   Student simply chooses a wire type of gauge that is consistent with their experimental results or discussion of gauge or wire types. Example: "Nichrome wire." This is sufficient enough as long as it had the shortest time marked in the data table.
2)  [Q2]   Student describes a way to fix the space heater that calls for an alternation that changes the density, diameter, length, or temperature of the wire used. Example: "If you replace the broken wire with one 36-gauge copper wire and one 32-gauge nichrome wire then when one breaks the other will keep the heater working," or "replace the broken wire with a nichrome wire and speed up the heater's fan."



Criterion A: 1) 36-gauge copper wire conducts more heat or has smaller diameter. or 2) 32-gauge copper, nichrome conducts less heat or steel has larger diameters. or 3) Increase gauge # and decrease wire diameter or decrease gauge # and increase wire diameter.

Criterion B:
1) Copper or Nichrome are materials that radiate more heat (As opposed to steel). or
2) Copper or steel are materials that radiate less heat (as opposed to nichrome). or
3) Describes mass or density of material.

Criterion C:
1) Redness or brightness when heat is radiated from wires. or
2) Wires heat up and are warmer. or
3) Larger gauge numbered wires melt through crayon faster, or smaller gauge numbered wires melt through crayon slower.

Criterion D: 1) Chooses a specific wire type and gauge that is consistent witht their experimental results and discussion. or
2) Describes some other way that would fix the space heater that would follow the concepts.


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