Blog 1: Notes on Current Electricity (pp. 544 ~ 552)

DEFINITIONS
electric current - a flow of charge, measured in amperes
current - the total amount of charge moving past a point in a conductor, divided by the time taken
- {I = Q/t} <-- I = current in amperes (A), Q = charge in coulombs (C) , t = time in second
ampere (A) - the base unit for current; equivalent to one coulomb per second [C/s]
coulomb (C) - the base unit for electric charge
conventional current - the model of positive charge flow
                               - http://www.youtube.com/watch?v=Y7Uqe6DyoRU [explanation]
ammeter - a current-measuring device
direct current (DC) - an electric current flowing in one direction only
load - a device that converts electric energy to other forms of energy
alternating current (AC) - an electric current that reverses direction in a circuit at regular intervals
circuit - the path of electric current flow from and to the power supply
electrical potential energy - energy stored when static electric charges are held a certain distance apart
electrical potential difference (V), or voltage - the electric potential energy for each coulomb of charge in a circuit
- {V = E/Q} <-- E is the energy required to increase the electric potential of a charge, Q
voltmeter - an instrument for measuring potential differences in volts
parallel circuit - a circuit in which loads are connected side by side

INFORMATION
16.2 Current
- What happens in an electric circuit:
       1. Electrons are provided with energy by an energy source.
       2. Conductors transport the electrons to the load (i.e. light bulb).

       3. The electrons get transported back to the energy source to be re-energized.

 - Conventionally, it was believed that current flow moves from the positive terminal to the negative terminal of any power supply. Although it is actually the electrons that are involved in current flows, the fact that positive charge flowing in one direction is mathematically same as the negative charge flowing in the opposite direction makes in which direction does the current flow move not matter. However, many people working in the field of electricity today still follow the conventional way of perceiving that it is the positive charge that flows in a current, and this model of positive charge flowing in a current is called conventional current. The model of negative charge flowing in a current is called electron flow.

- Frequently used symbols in circuit drawings:

                             (For more symbols, visit http://www.kpsec.freeuk.com/symbol.htm)

- Pertinent to the measurement of current:

          - ammeter: a device that measures current; must display excellence in conducting so that it does not affect the process of measuring current

          - circuit: the path that carries electric current flow from and to the power supply; required for any electrical device to work properly

16.3 Electrical Potential

- Electrical potential energy is the energy stored when static electric charges are held a certain distance apart. In order for the electrical potential energy of each coulomb of charge to increase, some kind of work has to be done by the power supply. The energy starts to decrease as the charge begins to flow through the load. 

          -  The equation for the energy transferred by charge flow:

             {E = VIt} E = energy (in Joules, J), V = potential energy (in volts, V), I = current (in amperes, A) t =  time (in seconds, s)
          - http://www.youtube.com/watch?v=elJUghWSVh4 [explanation]

- A voltmeter is utilized to measure the potential difference between two points. One of the important things to remember is to make sure that the voltmeter and the load are connected side by side, which will help compare the potential before and after the load. The other thing is that the voltmeter must be poorer in the ability to conduct that the connected load, so that the measurement by the voltmeter will not have much effect on the flowing of the current in the circuit.

SUMMARY OF EQUATIONS

1. [ I = Q/t ] -- current and charge

    I = current in amperes (A),

   Q = charge in coulombs (C) ,

    t = time in second

2. [ V = E/Q ] -- potential difference and energy

    V = electric potential difference (in volts, V)

    E = energy required to increase the electric potential of a charge (in joules, J)

    Q = charge carrying electric potential energy (in coulombs, C)

3. [ E = VIt ] -- electrical energy, and potential difference and energy

    E = energy (in joules, J)

    V = electric potential difference (in volts, V)

    I = current (in amperes, A)

    t = time (in seconds, s)

Helpful website:

http://www.allaboutcircuits.com/vol_1/index.html