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**Voltmeter**: A **voltmeter** is an instrument used for measuring electrical potential difference between two points in an electric circuit. Analog voltmeters move a pointer across a scale in proportion to the voltage of the circuit; digital voltmeters give a numerical display of voltage by use of an analog to digital converter.

**Potential difference**:** Voltage**, **electrical potential difference**, **electric tension** or **electric pressure** (denoted ∆*V* and measured in units of electric potential: volts, or joules per coulomb) is the electric potential difference between two points, or the difference in electric potential energy of a unit charge transported between two points.

**Electric field**: An **electric field** is generated by electrically charged particles and time-varying magnetic fields. The electric field describes the electric force experienced by a motionless electrically charged test particle at any point in space relative to the source(s) of the field. The concept of an electric field was introduced by Michael Faraday.

**Electron flow concept**: When Benjamin Franklin made his conjecture regarding the direction of charge flow (from the smooth wax to the rough wool), he set a precedent for electrical notation that exists to this day, despite the fact that we know electrons are the constituent units of charge, and that they are displaced from the wool to the wax — not from the wax to the wool — when those two substances are rubbed together. This is why electrons are said to have a *negative* charge: because Franklin assumed electric charge moved in the opposite direction that it actually does, and so objects he called “negative” (representing a deficiency of charge) actually have a surplus of electrons.

**Negative or positive direction**:

**Current flow**: An electric current is a flow of electric charge. Electric charge flows when there is voltage present across a conductor. In electric circuits this charge is often carried by moving electrons in a wire. It can also be carried by ions in an electrolyte, or by both ions and electrons such as in a plasma. The SI unit for measuring an electric current is the ampere, which is the flow of electric charges through a surface at the rate of one coulomb per second. Electric current can be measured using an ammeter. Electric currents cause many effects, notably heating, but also induce magnetic fields, which are widely used for motors, inductors and generators.

**Resistor symbol**:

**Carbon-composition resistor**: Carbon composition resistors (CCR) are fixed form resistors. They are made out of fine carbon particles mixed with a binder (for example clay). After baking it has a solid form. Although carbon composition resistors are widely applied in circuits, the majority of resistors are nowadays made by deposition of a metal or carbon film over a ceramic carrier.

**Ohm’s law** states that the current through a conductor between two points is directly proportional to the potential difference across the two points. Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equation that describes this relationship:

**DC circuits**: The basic tools for solving D C circuit problems are Ohm’s Law, the power relationship, the voltage law, and the current law. The following configurations are typical; details may be examined by clicking on the diagram for the desired circuit.

**Magnetism** is a class of physical phenomena that includes forces exerted by magnets on other magnets. It has its origin in electric currents and the fundamental magnetic moments of elementary particles. These give rise to a magnetic field that acts on other currents and moments. All materials are influenced to some extent by a magnetic field

In **alternating current** (**AC**, also **ac**), the flow of electric charge periodically reverses direction. In direct current (**DC**, also **dc**), the flow of electric charge is only in one direction. The abbreviations *AC* and *DC* are often used to mean simply *alternating* and *direct*, as when they modify *current* or *voltage*. AC is the form in which electric power is delivered to businesses and residences. The usual waveform of an AC power circuit is a sine wave. In certain applications, different waveforms are used, such as triangular or square waves. Audio and radio signals carried on electrical wires are also examples of alternating current. In these applications, an important goal is often the recovery of information encoded (or modulated) onto the AC signal.

**Key terms discussed on the download file:**

Elements of an Atom, Free Electrons, Conductors, Insulators, Semiconductors,

Voltage, Current, Direction of Current Flow, Kirchhoff’s current law, LED (light-emitting diodes), IC (integrated circuit), An integrated circuit ,monolithic integrated circuit , Electromotive force, emf, Inductance and Capacitance, Reactance and Impedance, Series and Parallel RLC Circuits, Power and Power Factor in an AC circuit, Transformers, Review Questions, current in a series circuit, magnetic field, magnetic lines of force, compass needle, iron filings, left-hand rule, clockwise magnetic flux, definition of magnetic flux, current-carrying coil, generators, direct current, alternating current, dc voltage, negative and positive terminals,

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