Right Hand Rules

Right Hand Rule #1 (for conventional current flow)

Thumb of right hand pointing in the direction of the conventional, or positive, current flow.

Right Hand Rule #2
Grasp the coiled conductor such that the curved fingers point in the direction of the positive current. The thumb points in the direction of the magnetic field within the coil.

Magnetism (New Unit)

17.1 The Magnetic Force - Another Force at a distance

- A magnetic field is the distribution of a magnetic force in the region of a magnet
- In a magnet, the north and south "characteristics" are what creates the magnetic forces
- Law of magnetic forces: dissimilar poles attract while similar poles repel
- To map a magnetic field, you would need to use a test compass
- Field lines can be mapped using a test compass
- Earth acts like a giant magnet, producing its own magnetic field.  Suggested theory states that this is because of the flow of hot liquid metals inside the Earth
- Domain theory of magnets: all large magnets are made up of smaller and rotatable magnets called dipoles.

17.2 Electromagnets

-Oersted's Principle: charge moving through a conductor produces a circular magnetic field around the conductor
- Right hand rules are hand signs that are designed to predict how magnetic forces act

16.5 - 16.6 Resistance Notes (Ohm's Law and Kirchoff's Law)

Definitions (words in bold in textbook):


Resistance: a measure of the opposition to current flow.
Ohm's Law: the principle that the electric current passing through a conductor is directly proportional to the potential difference across it.
Gauge number: the number on a wire that indicates its cross-sectional area
Series Circuit: a circuit in which the loads are connected one after another in a single path
Parallel Circuit: a circuit in which the loads are connected side by side and there are many paths
Kirchoff's current law: the law that states the total current at a point in the circuit equals the total current that flows out
Kirchoff's voltage law: the law that states that the total of all electrical potential decreases must be equal to the total of all electrical potential increases in a complete circuit
Conservation of electric charge & Conservation of energy: in any circuit, there is no net gain or loss of electric charge or energy

Info:
16.5 Resistance - Ohm's law

- Amount of current depends on two things: 1. the potential difference of the power supply 2. the nature of the pathway through the loads
- the more difficult the path, the more opposition there is to flow a.k.a. resistance
- when graphing Voltage vs. Current of a circuit, the slope of the graph ( V/I ratio) is constant. therefore the slope and the v/i ration must represent the resistance of the load because the resistance remained unchanged
- R = V/I, where R is given the unit "ohms" after Georg Simon Ohm who discovered this relationship
- Factors that determine resistance of a conductor:
     -   length
     -   cross-sectional area
     -   material that it is made of
     -   temperature


16.6 Series and Parallel Circuits


- Resistance in a series circuit
R = R1 + R2 + R3 .... + Rx

- Resistance in a parallel circuit
1/R = 1/R1 + 1/R2 + 1/R3 .... + 1/Rx

Prelab Chart

Energy Ball Questions #1-12

1. Can you make the energy ball work? What do you think makes the ball flash and hum?

   Yes, you can make the energy ball work by simply placing both fingers on both the metal strips.  Our fingers are conducting a current of electrons through our body into the energy ball.

2. Why do you have to touch both metal contacts to make the ball work?

   By touching both metal contacts, we are creating a complete circuit for the electric current to flow through. If we only touched one of the contacts, there would not be a complete circuit which would mean the current could not continuously flow in and out of two terminals. 

3. Will the ball light up if you connect the contacts with any material?

    No, the ball will only light up if you connect the contacts with conductors.  For instance, metallic objects and the human touch would both work, but objects such as wood or rubber would not. 

4. Which materials will make the energy ball work? Test your hypothesis.


    Any materials that can conduct electricity fairly well will work. We tested this hypothesis by using the metal strips on the caps of our pens.  In this case, we needed to touch the both the metal strips on the caps with our fingers (providing a complete circuit), before touching the metal contacts on the energy balls. We believed that this test proved our hypothesis correct.


5. This ball does not work on certain individuals - what could cause this to happen?

    If the individual has a non-conductor between the metal contacts and their skin. Or if the individual is dead, and their body is not producing the electric signals that every living human should be producing.  

6. Can you make the energy ball work with all 5 - 6 individuals in your group? Will it work with the entire class? 

    Yes, we were able to make it work with all 5 individuals in our group. We had two separate people each touch a metal strip and formed a 5-person series circuit that joined the two people.  In order for the energy ball to work, everybody had to be touching the people beside them to form a complete circuit.  Based on this idea, it will indeed work with the entire class as long as everybody is touching in some way.    

7. What kind of a circuit can you form with one ball?

     We would form a series circuit that has a direct current.  


8. Given 2 balls (combine 2 groups): Can you create a circuit where both balls light up? [1/3]


      Yes, we were able to create both a series circuit and parallel circuit where both balls lit up.


9. What do you think will happen if one person lets go of another person's hand and why? [2/3]

     If the circuit is a series circuit, than both balls would go out no matter who breaks the complete circuit.  However, if the circuit is a parallel circuit,  depending on who lets go, only one ball will go out and one ball will stay lit.

10. Does it matter who lets go? Try it. [3/3]

     In a series circuit, it does not matter who lets go, both energy balls will stop working.  This is because both energy balls are connected in one continuous circuit, where there is only one path for the current to flow in. Therefore, if that one path is broken even by one person, than the current cannot flow to either balls.
     However, in a parallel circuit, it does matter who lets go.  This is because there is multiple paths for the current to take.  If one person breaks the circuit, the current can still reach one energy ball depending on where the circuit is not complete.  

11. Can you create a circuit where only one ball lights (both balls must be included in the circuit)? [1/2]

    Yes, you can do this using a parallel circuit.  However, one of the paths in the parallel circuit must be broken or not completed.  

12. What is the minimum number of people required to complete this? [2/2] 

     There needs to be a minimum of four people.  
    

Physics Challenge

The physics of tall structures:
  
     When building a tall structure, you need to consider many factors in order to ensure the structure is stable enough and will not fall or tip over at the smallest gust of wind. For this challenge, groups were required to build the tallest free-standing structure they could using rolls of newspaper.  Although sadly, I was not here for the challenge and did not get to participate, I learned a lot about the methods that my fellow classmates (and famous architects!) incorporated into their designs.
     For instance,  many groups used a heavy base made up of legs in a triangular or square based pyramid. They used this heavy base to support a very tall, thin, but light tower that got thinner as it progressed higher. This seemed to work the best for many of the groups who made sure to properly proportion the thickness of their tower.
     In real life, architects have to consider many more factors when designing a tall structure. For instance, weather conditions (such as the wind), location, area, and so on.  But what generally remained the same between the class ideas and an architect's ideas was that the base had to be heavy and strong enough to support a lighter upper mass. However, in real life, many architects tend to use more complex shapes and designs to successfully stabilize a structure while maintaining an aesthetically pleasing look.


What makes a tall structure stable?

     The most important thing when designing a tall structure is that is able to hold itself up.  Therefore, tall structures must be carefully planned out, from the base up.  Many different tall structures use different mechanisms and designs to remain stable.  For instance, the CN Tower in Toronto, Canada, has a massive underground foundation, that supports a thin, rising, and relatively light shaft that got progressively thinner. For the Burj Khalifa in Dubai, a more complicated "buttressed core" design (a hexagonal core reinforced by three buttresses arranged in a Y-shaped) along with another huge base, were used.

What is the centre of gravity?

   The centre of gravity is a geometric property of any object that every architect must consider when designing a building.  By definition, the centre of gravity is the average location of an object's weight, or in other words, the mean location of the gravitational forces acting on the object. Note*: the centre of gravity does not always have to be in the exact centre of an object, especially if the upper and lower halves are not perfectly symmetrical.
  

1. Current Electricity (Notes)

Definitions:

Current: Rate of Charge Flow (symbol: I)
   
      - Direct Current (DC): current that flows in a single direction from the power supply through the conductor to a load and back to the power supply
      - Alternating Current (AC): current that continually changes direction

Conventional Current: Model of positive charge flow  (+) to (-)
Ammeter: a current-measuring device
Circuit: complete path of electric current flow from and to the power supply
Voltage: electric potential difference (symbol: V)
Voltmeter: an instrument used to measure potential difference between any two points

Equations: 
1. Current
(Total amount of Charge in Coulombs divided by Time)
I = Q/T, Q = IT, T = Q/I

2. Voltage (Electric Potential Difference)
(energy over charge)
V = E/Q

Circuit Symbols: