*e*on electron is negative and has magnitude of 1.602 x 10

^{-19}and the proton carries the same magnitude as electron but positive charge.

## Electric Charge

Every electrical phenomena is based on basic concept of electric charge.

*Electric charge*is also the most fundamental quantity of electric circuit. The elctric charge's meaning is shown below :Charge is an atomic particles in electrical system, measured in coulombs (C)

Some points we need to take note are shown below :

- Large unit of charges is Coulomb. For every 1 C of charge contains 1/(1.602 x 10
^{-19}) = 6.24 x 10^{18}electrons. - From experiment observatory, the only charges that happen in nature are integral multiplies of electronic charge
*e*= -1.602 x 10^{-19}C. - From "
*Law of Conservation of Charge*" states that charge can not be created or destroyed, it can only be transferred from a point to another where it can be converted to other energy form.

## Electric Current

Before moving to next part, let us take a look a short explanation below :

Electric current is the change of charge in a period of time, measured in amperes (A)

In mathematic equation, the relationship between current

*i*, charge*q*, and time*t*is expressed as :
i = current (A)

and

**1 ampere = 1 coulomb/second**

We can obtain the transferred charge between time

*t*and_{o}*t*using integral for both sides. Equation.(2).(2) |

Looking back to Equation.(1), the current do not need to be in constant-value function. For further explanation, we will find there will be a variation changes of charge. There are two types of current.

After learn about electric current, you need to learn about electrical voltage.

If a current has constant value over time or its value does not change with time, we call it

*direct current*(dc) as we can see in Figure.(2).The symbol of constant current isa direct current (dc) is a current which has constant value with time changing.

*I*.

A changing current over time is represented by

An alternating current (ac) is a current that varries sinusoidally in a time period.

*i*symbol. This time-changing current is represented by alternating current (ac). The alternating current has the sinusoidal waveform shown in Figure.(3).An alternating current (ac) is a current that varries sinusoidally in a time period.

Figure 3. Alternating current waveform |

For reminder, the current direction will refer to positive charge direction of flow.

**1. How many charge in 4.600 electrons?**

__Solution :__
Every electron has -1.602 x 10

^{-19}C. Thus 4.600 electrons will have -1.602 x 10^{-19}x 4.600 = -7.369 x 10^{-16 }C.**2.Total charge entering one terminal is q = 5t sin4πt mC. Calculate the current at t = 0.5 s.**

__Solution :__**3.Calculate the total charge entering a terminal for a period time from t =1 s to t = 2 s if the current is i = (3**

*t*^{2}-*t*) A.

__Solution :__
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