Introduction to Basic Direct Current (DC) Electrical Theory PDF

Introduction to Basic Direct Current (DC) Electrical Theory: NOTE: In accordance with Swedish conventions, in these notes we have used the symbol U to denote voltage. However, in many English language texts you will usually see the symbol V to denote voltage. [The symbol U comes from the Germa...

Introduction to Basic Direct Current (DC) Electrical Theory: NOTE: In accordance with Swedish conventions, in these notes we have used the symbol U to denote voltage. However, in many English language texts you will usually see the symbol V to denote voltage. [The symbol U comes from the German word Unterschied, which means "difference".] Introduction Direct Current (DC) (Likström) is a type of electrical current where the flow of electrons is in a single, constant direction. It is the most fundamental form of electricity and serves as the foundation for many electrical systems and components. Some Basic Concepts: 1. Electrical Charge (Elektrisk Laddning) Definition: Electrical charge is a fundamental property of particles such as electrons and protons. Electrons carry a negative charge, while protons carry a positive charge. Unit: Coulomb (C) Concept: In electrical circuits, the movement of charges (typically electrons) constitutes electric current. 2. Electric Current (Elektrisk Ström) Definition: Electric current is the flow of electric charge through a conductor, such as a wire. In DC circuits, the current flows in one direction. 𝑄 Formula: 𝐼 = , where I is the current in amperes (A), Q is the charge in coulombs (C), and T 𝑇 is time in seconds (s). Unit: Ampere (A) Concept: In a DC circuit, the direction of current remains constant. This is different from alternating current (AC), where the flow direction changes periodically. 3. Voltage (Spänning) Definition: Voltage, also known as electrical potential difference, is the force or "pressure" that pushes electric charges through a conductor. 𝑊 Formula: U= , where U is the voltage in volts (V), W is the work or energy in joules (J), and 𝑄 Q is the charge in coulombs (C). Unit: Volt (V) Concept: Voltage is analogous to water pressure in a pipe system. In DC circuits, the voltage across components remains steady, unlike AC systems where voltage varies. Page 1 of 4 4. Resistance (Resistans) Definition: Resistance is a property of a material that opposes the flow of electric current. Different materials have different resistances based on their physical properties. 𝑈 Formula: 𝑅 = , where R is the resistance in ohms (Ω), U is the voltage in volts, and I is the 𝐼 current in amperes. Unit: Ohm (Ω) Concept: Materials like copper have low resistance and are good conductors, while materials like rubber have high resistance and are insulators. 5. Ohm’s Law (Ohms Lag) Definition: Ohm's Law describes the relationship between voltage (U), current (I), and resistance (R) in an electrical circuit. Formula: 𝑈 = 𝐼 ∗ 𝑅 Concept: If you know any two of the values in this equation, you can calculate the third. For instance, if you know the voltage and resistance, you can calculate the current. 6. Power (Effekt) Definition: Power in a DC circuit is the rate at which electrical energy is converted to another form of energy, such as heat, light, or mechanical energy. Formula: 𝑃 = 𝑈 ∗ 𝐼, where P is power in watts (W), U is voltage in volts, and I is current in amperes. Unit: Watt (W) Concept: Power tells us how much energy is being used or generated in the circuit. 7. Energy (Energi) Definition: Energy in electrical terms is the capacity to do work, and in a DC circuit, it is typically supplied by a battery or power supply. Formula: 𝑊 = 𝑃 ∗t, where W is energy in joules (J), P is power in watts (W), and t is time in seconds. Unit: Joule (J) Concept: Energy is consumed over time as power is used to do work, such as lighting a bulb or running a motor. Page 2 of 4 8. Electrical Components in DC Circuits Battery (Batteri): A source of DC voltage that supplies energy to the circuit. Resistor (Resistor): A component that resists the flow of current and creates a voltage drop in the circuit. Capacitor (Kondensator): A component that stores energy in an electric field, though in pure DC circuits, it acts as an open circuit after charging. Switch (Brytare): A device used to open or close a circuit, controlling the flow of current. LED (Lysdiod): A diode that emits light when current flows through it. 9. Series and Parallel Circuits (Seriekrets och Parallellkrets) Series Circuit (Seriekrets): In a series circuit, components are connected end-to-end, and the same current flows through each component. The total resistance is the sum of individual resistances. Total Resistance: Rtotal = R1+R2+R3+… Parallel Circuit (Parallellkrets): In a parallel circuit, components are connected across the same two points, and the voltage across each component is the same. The total resistance is less than the smallest individual resistance. 1 1 1 1 o Total Resistance: = + + … 𝑹𝑡𝑜𝑡𝑎𝑙 𝑹1 𝑹2 𝑹3 10. Kirchhoff’s Laws (Kirchhoffs Lagar) Kirchhoff’s Current Law (KCL) (Kirchhoffs Strömlag): The total current entering a junction is equal to the total current leaving the junction. o Formula: ∑ Iin = ∑ I out Kirchhoff’s Voltage Law (KVL) (Kirchhoffs Spänningslag): The total voltage around any closed loop in a circuit is equal to the sum of the individual voltage drops. o Formula: ∑ U = 0 Page 3 of 4 GLOSSARY Swedish Term English Term Description Batteri Battery A device that stores chemical energy and converts it to electrical energy. Brytare Switch A device for opening and closing a circuit. Effekt Power The rate at which energy is used or produced in a circuit. Elektrisk Electrical Charge Property of subatomic particles that causes them to Laddning experience a force. Elektrisk Ström Electric Current The flow of electric charge in a circuit. Energi Energy The ability to do work, stored or transferred as electrical energy. Kirchhoffs Kirchhoff’s Voltage The sum of all voltages in a closed loop equals zero. Spänningslag Law Kirchhoffs Kirchhoff’s Current The total current entering a junction equals the total Strömlag Law leaving. Kondensator Capacitor A device that stores electrical energy in an electric field. Lysdiod LED (Light- A semiconductor device that emits light when current Emitting Diode) flows through it. Motstånd Resistance Another term for resistance, often used in daily language. Ohms Lag Ohm’s Law The relationship between voltage, current, and resistance. Öppen krets Open Circuit An incomplete path that prevents current from flowing. Parallellkrets Parallel Circuit A circuit in which components are connected across common points, sharing the same voltage. Resistans Resistance Opposition to the flow of current in a material or circuit. Resistor Resistor A component that limits the flow of current in a circuit. Seriekrets Series Circuit A circuit in which components are connected end-to-end, so the current is the same. Sluten krets Closed Circuit A complete electrical connection allowing current to flow. Spänning Voltage The potential difference that drives current through a circuit. Strömkälla Power Source A device or system that supplies electrical energy. Page 4 of 4