Reviewing Homework

Emily reviewed last night's homework– the students had some trouble solving all of the problems, so we reviewed the most important points to remember while solving particular types of problems:

Sticky Tape Problem
Two tapes which were prepared the same way would repel each other. Two tapes prepared in different ways would attract each other. A piece of tape can also be neutral. After looking at what is given, look for a piece of tape with a repelling charge first to more easily solve a problem.

Light Bulbs Problem
Flow Model: Each battery has voltage and puts out a current which moves through wire and various obstacles. Current will come from the battery to light the light bulb, flow through the circuit, and back into the battery. Current will flow out of the battery when a circuit is complete. A circuit is complete when one wire is touching the positive (+) end of the battery and is also touching the negative (-) end of the battery. The current could also travel through a bulb, however a bulb is not necessary to have a complete circuit. The current which the battery “puts out” is dependent on the number of obstacles that it has to move through. Less current is “put out” with less obstacles.

Complete Circuit- path through which “something” can flow from battery, through wires, and back to the battery.

Series Circuit- a single circuit with two bulbs connected. Will be dimmer than if a single bulb were connected, but bulbs will be equally bright to each other.


(Source: http://www.google.com/imgres?hl=en&sa=X&biw=1024&bih=456&tbm=isch&prmd=imvns&tbnid=Wj75DbwaWitEAM:&imgrefurl=http://www.berkeleypoint.com/learning/parallel_circuit.html&docid=FAvb7yusysAviM&imgurl=http://www.berkeleypoint.com/images/series.jpg&w=385&h=237&ei=2ao6T9SSKcahiQK5-JSUDA&zoom=1&iact=rc&dur=412&sig=104116790102875307504&page=1&tbnh=84&tbnw=136&start=0&ndsp=12&ved=1t:429,r:8,s:0&tx=71&ty=13) Parallel- two bulbs connected to the battery with their own paths to the battery. This allows the battery to release more current because there are more paths to travel. Battery will drain faster because it uses more current.


(Source: http://www.google.com/imgres?um=1&hl=en&biw=1024&bih=499&tbm=isch&tbnid=jHvaX54Oj0hGYM:&imgrefurl=http://www.berkeleypoint.com/learning/parallel_circuit.html&docid=FAvb7yusysAviM&imgurl=http://www.berkeleypoint.com/images/parallel.jpg&w=194&h=422&ei=LKo6T9LiOobUiAK97-STDA&zoom=1)
Short Circuit- battery will not light a bulb when there is a path of least resistance for the current to travel through. It will take the easier path.

• Think about “something” moves through wires and bulbs and battery without being “used up” – flow or current
  
• If we have a branch in current, “something” divides flow through the branches and recombines to travel back to the battery
  
• Brightness of bulb indicates the amount of “something” flowing through the bulb (if the bulb doesn't light, it might be “out” and there will be no flow, or there may not be enough flow to light the bulb
  
• The amount of flow out of the battery depends on what the circuit is attached to (series, parallel, etc.)
  

Mathematics with Circuits
Example:
V = I/R→R = V\I
R1 = RD = RE
Equivalent Resistance = 2 x R1
V1/2R1 ***Looking at current moving through Bulb D and Bulb E

What is current through branch DE v1 R1 = v1 (same voltage throughout entire circuit) 2R1
v1/2R1