## Electric current

**1**. A copper wire is traversed by a constant electric current of intensity 7A. Knowing that What is the modulus of electrical charge that crosses a conductor cross section for a second? And how many electrons cross such a region in this time interval?

*To solve the first part of the problem we must remember the definition of electric current:*

*Overriding the values given in the exercise:*

*To solve the second part of the exercise we just need the equation of electric charge quantization:*

**2.** Given the figure below:

Calculate the intensities of currents 1 and 2.

*Recalling the condition of continuity of electric current (Kirchoff's 1st Law):*

*In the first node:*

*On the second node:*

*Recalling that the total current that reaches the system cannot be changed, in this case, we only need to know the total current, and use the value we already know for current 1:*

*Reducing from this total the known value:*

## Electrical resistance

**1.** The table below describes the electric current as a function of voltage in an ohmic resistor kept at constant temperature:

i (a) | U (V) |

0 | 0 |

2 | 6 |

4 | 12 |

6 | 18 |

8 | 24 |

Calculate the resistance and explain what it takes to call this ohmic conductor.

*An ohmic conductor is characterized by not changing its resistance when current or voltage change, so that the product between the two remains constant.*

*If the described resistor is ohmic, just calculate the resistance in one of the given data (except 0V, because when there is no voltage there can be no current), this calculation is given by:*

## Resistors Association

**1. **Given the resistor associations below, state your type of association, justify and calculate the total resistance of the association.

THE)

Where:

*Circuit A is an association of series resistors, as there is only one way for the current to flow from one end to the other and it must pass through each resistor successively.*

*The calculation of the total resistance of the circuit is made by the sum of each resistance that forms it, that is:*

B)

Being:

* Circuit B is an association of resistors in parallel, as there are secondary paths to be used by the current, which allows two resistors to be traversed by electric current at the same instant.*

*The calculation of the inverse of the total circuit resistance is made by the sum of the inverses of each resistor, ie:*