Text book P553-P563 notes taking

1. The measure of this opposition to flow is called electrical resistance.
2. R=V/ I  R is the resistance in volts/ ampere, given the derived unit of ohm.
3. V/I ratio was constant for a particular resistor. this ratio is called Ohm's law.
4.---the larger the conductor the greater the resistance.
   ---the larger the cross-sectional area of the conductor, the less resistant it has to change flow.
   ---the type of the material--some materials are better conductor than others.
   ---higher temperatures tends to increase the resistance.
5. A wire that has a small gauge number has a large cross-sectional area. A small cross-section has a large   gauge number.
6. A series circuit the loads are connected one after another is single path.
7. A parallel circuit the loads are connected side by side.
8. Kirchhoff's current law: the total amount of current into a junction point of a circuit equals the total current that flows out of that same junction.
9. Kirchhoff's voltage law: the total of all electrical decreases in any complete circuit loop is equal to any potential increases in that circuit loop.
10. ---in series circuit------IT=I1=I2=I3
                                                       VT=V1+V2+V3
                                                        RT=R1+R2+R3
        ------in parallel circuit------IT=I1+I2+I3
                                                          VT=V1=V2=V3
                                                          1/RT=1/R1+1/R2+1/R3

Name                         Symbol           Unit          Definition

Potential different         V                V (volt)     The electrical potential energy for    
                                                                                  each coulomb of charge.
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Current                        I                 A(ampere)       The rate of charge flow.

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Resistance                   R               ohm                 The opposition to current flow.

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  Power                      P              W(watts)      The rate at which electrical energy
                                                                    is passed on the various circuit load.
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                                                                                                  .            

Parallel and Series Circuit

What is the different between a parallel and series circuit?

In a series circuit the loads are connected one after another in a single path

In a parallel circuit loads are connected are side by side

 

Question 1-12 of energy ball

1.Can you make the energy ball work? What do you think makes the ball flash and hum?
   Yes we can make the energy ball work.  We touch both metal contacts complete the circuit, there is     current go though the energy ball, so the ball can flash and hum.
2. Why do you have to touch both metal contacts to make the ball work?
   We have to touch both metal contacts to complete the circuit, make the ball work.
3. Will the ball light up if you connect the contacts with any material?
    No, the ball will not light up with any material except conductors such as metal and water...
4.Which materials will make the energy ball work?
  Conductors, for example, metal, water, ourselves...
5.This ball does not work on certain individual, what could cause this to happen?
  When the skin is very dry this ball does not work.
6.Can you make the energy ball work with 5-6 individuals in your group? Will it work with the entire class?
   Yes, and it works with the entire class.
7.What kind of a circuit can you form with one energy ball?
   I can form simple circuit with one energy ball.
8.Given two balls, can you create a circuit where both balls light up?
  Yes we can.
9.What do you think will happen if one person lets go of the other person's hand and why?
   The ball will not light up, because the circuit is opened, no current go though the energy ball.
10.Does it matter who let's go?

     No, it does not matter
11.Can you create a circuit where only one ball lights up (both balls must be included in the circuit)？
    Yes, form a series circuit.
12.What is the minimum number of people required to complete this?
    At least five people required to complete this.

Struchure challenge.

What make a tall structure stable?

• make the top skinny and the base wide
• the base must be heavier then the top
• the centre of gravity need to be lower
• need more support point

Centre of gravity :  is the average of the weight of an object.  For every object the weight  acts through the center of gravity. Centre of gravity is very important for the flying objects.

Notes on current electricity

• Electrons in a static state have energy.
• Current (I) is the total amount of charge (Q) moving past a point in a conductor divided by the time taken. I=Q/T
• Current flow was thought to move from the positive terminal to the negative terminal.
• An ammeter mus be wired so that all current flows through it.
• Direct current, like a light bulb or other device uses energy.
• V=E/Q    electric potential difference\voltage (v)   increase the electric (E)
• E=VIT
• Potential difference between any two points can be measured using a voltmeter.
• A voltmeter must be connected in parallel with a load.
• The voltmeter must have a large resistance.