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Kirchhoffs first rule

Kirchhoff’s first rule 1 Kirchhoff’s first rule also called the rule of junction point states that the electric current that enters a junction point is the same as the electric current exit from that junction point. The junction point in an electrical circuit is the point where two or more of the two conductors meet, such as point a in the figure on the side.

I is the electric current that enters the junction point, while I₁and I₂ are the electric currents that exit from the junction point, I = I₁ + I₂. Another example, observe the figure below.

Kirchhoffs second rule

Kirchhoff’s second rule states that the change in electric potential on the circumference of a closed circuit is zero. Kirchhoff’s second rule is based on the law of conservation of energy, which states that energy is eternal.

Kirchhoff’s second rule 1 To better understand this, imagine the electric charge moving in a closed circuit, as in the figure. When an electric charge passes through an electrical resistance (R), the electrical potential energy is reduced because it is used on these resistances. If the electric charge passes through another electrical resistance, the electric potential energy decreases again because it is used again on the resistance. Furthermore, when the electric charge passes through the voltage source from a low potential to a high potential, the electric potential energy increases. When it returns to its original point, the electric potential energy is the same as before, where the change in electrical potential energy is zero. When applying Kirchhoff‘s second rule to an electrical circuit, we use the change in electrical voltage, not the change in electrical potential energy.

Definition of electric power

The power learned in the work and Energy is defined as the work done during a certain time interval. Work is a process of energy change so that power can be understood as a change in energy that occurs during a certain time interval.

Electric power is a change in electrical energy during a certain time interval. In a review of electrical potential, it is explained that changes in electric potential energy occur when an electric charge passes through an electric potential difference.

Angular momentum

Angular momentum The quantity of the rotational motion, which is identical to mass (m) in the linear motion, is the moment of inertia (I). The quantity of the rotational motion, which is identical to the velocity (v) in the linear motion, is the angular velocity (ω). Thus, the rotating object has angular momentum that can … Read more

Moment of inertia

1. Moment of inertia of the particle

Moment of inertia 1 Review a rotating particle. The particle with mass m is given the force F so that the particle rotates about the axis O. The particle is r apart from the axis of rotation. First, the particle is in rest (v = 0). After moved by the force of F, the particles move with a certain speed so that the particles have tangential acceleration. The relationship between force (F), mass (m), and the tangential acceleration of particles are expressed by equation 3:

Definition of Electric current

In a conductor such as copper, there are electrons that move randomly at high speed freely but not escape from the metal. Electrons that can move freely are called free electrons. Although the electrons move freely in all directions, there is no total flow of electrons in a particular direction. This condition occurs when there is no potential difference between the two ends of the copper wire.

When the wire is connected to an electrical source, a potential difference arises between the two ends of the copper wire, so that an electric field appears within the copper wire. The existence of an electric field causes free electrons to experience the electric force F = q E = e E, where F = electric force, e = electron charge, E = electric field. This electric force causes all the electrons that are moving freely to accelerate together, which is the same direction as the electric force.

5 Parabolic motion Work and kinetic energy Linear momentum Linear and angular motion Problems and Solutions

1. A ball is thrown from the top of a building with an initial speed of 8 m/s at an angle of 20^o below the horizontal. The ball hits the ground 3 seconds later.

a) How far from the bottom of building the ball touches the ground

b) How high is the ball thrown from the place

c) How long the ball reaches a height of 10 m from the place of throwing

Article about the Definition of capacitor

The definition of capacitor is a device that stores electrical charge and electrical potential energy. The simple capacitor consists of two-conductor plates or sheets that are placed close together but do not touch each other and are separated by an insulator or a vacuum. Conductors are materials that can conduct electric current such as metals, while insulators are materials that cannot conduct electric current such as plastic.

At first, the two conductors are not electrically charged or electrically neutral. In order for one conductor to be positively charged and the other conductor to be negatively charged, then there must be a transfer of electrons from one conductor to another. The electrons are on the surface of the atom, so they are easy to move. After the electron has moved from one conductor to another, one of the conductors has an excess of electrons (lack of protons)

so that it becomes negatively charged, while the other conductor has an electron deficiency (excess proton) so that it becomes positively charged. A detailed description of the process of charging electric charges on capacitors is reviewed on the topic of storing electrical energy in capacitors.

Definition of the electric potential

Electric potential is defined as the electric potential energy per unit charge. Suppose that when it is at point a, the charge q has the electric potential energy equal to EP_a, then the electric potential at point a is formulated as follows:

V = electric potential, EP = electric potential energy, q = electric charge

V is not only at point a but also at all points in the electric field. Point a is used as an example. As will be explained later, the V does not depend on the charge q.

Article about the Electric potential energy

Before studying this topic, first understand work, the conservative forces, the relationship between the conservative forces with potential energy, the electric forces and the electric field.

Electric force is the conservative forces

In addition to the gravitational force and spring force, the other example of the conservative force is the electric force. To better understand why the electric force is called the conservative force, understand the following explanation.