Group 11 PDF - Ohm's Law, Energy & Power, Electrical Safety

Group 11 Ohm’s Law, Energy & Power in Electric Circuits & Electrical safety, Devices for measuring circuits and voltages OHM’S LAW  In order to understand Ohm’s law, We should be able to describe current, voltage and resistance and their standard units of me...

Group 11 Ohm’s Law, Energy & Power in Electric Circuits & Electrical safety, Devices for measuring circuits and voltages OHM’S LAW  In order to understand Ohm’s law, We should be able to describe current, voltage and resistance and their standard units of measurement. Ohm’s Law The relationship between Voltage, Current and Resistance in any DC electrical circuit was firstly discovered by the German physicist Georg Simon Ohm. Ohm found that, at a constant temperature, the electrical current flowing through a fixed linear resistance is directly proportional to the voltage applied across it, and also inversely proportional to the resistance. Ohm’s Law V This law is the most I= R fundamental relation in the analysis of electrical circuit. It connects the relationship of the quantities of voltage, Where: electric current and resistance I - Current in one easy-to-use equation V - Voltage R - Resistance Rearrange the terms in order Or simply remember this to solve the equation for a Ohm’s Law Triangle specific unit of measurement Current (I) = Voltage (V) / Resistance (R) Voltage (V) = Current (I) x Resistance (R) Resistance (R) = Voltage (V) / Current (I)  Sample Problem You have a circuit with a source voltage of 12 V and a resistance of 15 Ω. What is the current in the circuit?  Sample Problem ANSWER: You have a circuit with a What are the given in the problem? source voltage of 12 V V = 12 V and a resistance of 15 Ω. R = 15 Ω What is the current in the What is the unknown? circuit? I = ? What is the formula? I = V/R  Sample Problem ANSWER: You have a circuit with a source voltage of 12 V and a resistance of 15 Ω. I = V/R What is the current in the I = 12 V/15 Ω circuit? I = 0.8 A  Try this! What is the voltage of a circuit with a resistance of 9 Ω and a current of 3 A?  Try this! ANSWER: What is the voltage of a Given: Unknown: Formula : circuit with a resistance R=9Ω V=? V = IR of 9 Ω and a current of 3 I=3A A? Solution : V= (3 A) (9 Ω) V = 27 V ENERGY & POWER IN ELECTRIC CIRCUIT  / ENERGY IN ELECTRIC [{{{[ CIRCUIT Energy is the ability to do work, and in electric circuits, it is measured in joules (J). When a current flows through a circuit, it does work on the circuit elements, such as resistors or motors. The amount of work done is equal to the energy consumed by the circuit. The energy consumed by the circuit can be calculated by multiplying the voltage across the circuit by the current flowing through it and the time the current is flowing, using the formula:  / ENERGY IN ELECTRIC [{{{[ CIRCUIT Energy is the ability to do work, and in electric circuits, it is measured in joules (J). When a current flows through a circuit, it does work on the circuit elements, such as resistors or motors. The amount of work done is equal to the energy consumed by the circuit. The energy consumed by the circuit can be calculated by multiplying the voltage across the circuit by the current flowing through it and the time the current is flowing, using the formula: Energy (J) = Power (W) x Time (s)  / ENERGY IN ELECTRIC [{{{[ CIRCUIT Energy is the ability to do work, and in electric circuits, it is measured in joules (J). When a current flows through a circuit, it does work on the circuit elements, such as resistors or motors. The amount of work done is equal to the energy consumed by the circuit. The energy consumed by the circuit can be calculated by multiplying the voltage across the circuit by the current flowing through it and the time the current is flowing, using the formula: Energy (J) = Power (W) x Time (s) where Power (W) = Voltage (V) x Current (A) is the rate at which energy is consumed by the circuit.  / ENERGY IN ELECTRIC [{{{[ CIRCUIT Sample Problem: A 9-volt battery is connected to a resistor with a resistance of 15 ohms, and a current of 0.6 amperes flows through the resistor for 10 seconds; calculate the energy consumed by the circuit and the power consumed by the resistor.  / ENERGY IN ELECTRIC [{{{[ CIRCUIT Sample Problem: A 9-volt battery is connected to a resistor with a resistance of 15 ohms, and a current of 0.6 amperes flows through the resistor for 10 seconds; calculate the energy consumed by the circuit and the power consumed by the resistor. Power = Voltage × Current Power = 9 V × 0.6 A Power = 5.4 W  / ENERGY IN ELECTRIC [{{{[ CIRCUIT Sample Problem: A 9-volt battery is connected to a resistor with a resistance of 15 ohms, and a current of 0.6 amperes flows through the resistor for 10 seconds; calculate the energy consumed by the circuit and the power consumed by the resistor. Power = Voltage × Current Energy = Power × Time Power = 9 V × 0.6 A Energy = 5.4 W × 10 s Power = 5.4 W Energy = 54 J  / ENERGY IN ELECTRIC [{{{[ CIRCUIT Sample Problem: A 9-volt battery is connected to a resistor with a resistance of 15 ohms, and a current of 0.6 amperes flows through the resistor for 10 seconds; calculate the energy consumed by the circuit and the power consumed by the resistor. The power consumed by The energy consumed by the resistor is 5.4 watts. the circuit is 54 joules.  / ENERGY IN ELECTRIC [{{{[ CIRCUIT Alternative Formulas for Current and Voltage From the power equation, you can solve for I or V: Current (I) = Power (W) / Voltage (V) Voltage (V) = Power (W) / Current (I)  / POWER IN ELECTRIC [{{{[ CIRCUIT Power is the rate at which energy is consumed or produced, and in electric circuits, it is measured in watts (W). Power can be calculated by multiplying the voltage across the circuit by the current flowing through it, using the formula:  / POWER IN ELECTRIC [{{{[ CIRCUIT Power is the rate at which energy is consumed or produced, and in electric circuits, it is measured in watts (W). Power can be calculated by multiplying the voltage across the circuit by the current flowing through it, using the formula: Power (W) = Voltage (V) x Current (I)  / POWER IN ELECTRIC [{{{[ CIRCUIT Using Ohm’s Law (V = IR), Power can be also expressed as:  / POWER IN ELECTRIC [{{{[ CIRCUIT Try This! Suppose you have a circuit that consists of a 24-volt battery connected to a resistor with a resistance of 8 ohms. If a current of 3 amperes flows through the resistor for 4 seconds, (a) what is the energy consumed by the circuit, and (b) what is the power consumed by the resistor?  / POWER IN ELECTRIC [{{{[ CIRCUIT Try This! Suppose you have a circuit that consists of a 24-volt battery connected to a resistor with a resistance of 8 ohms. If a current of 3 amperes flows through the resistor for 4 seconds, (a) what is the energy consumed by the circuit, and (b) what is the power consumed by the resistor? Calculate the power consumed by the resistor. Power = Voltage × Current Power = 24 V × 3 A Power = 72 W  / POWER IN ELECTRIC [{{{[ CIRCUIT Try This! Suppose you have a circuit that consists of a 24-volt battery connected to a resistor with a resistance of 8 ohms. If a current of 3 amperes flows through the resistor for 4 seconds, (a) what is the energy consumed by the circuit, and (b) what is the power consumed by the resistor? Calculate the power Calculate the energy consumed by the resistor. consumed by the circuit. Power = Voltage × Current Energy = Power × Time Power = 24 V × 3 A Energy = 72 W × 4 s Power = 72 W Energy = 288 J  / POWER IN ELECTRIC [{{{[ CIRCUIT Try This! Suppose you have a circuit that consists of a 24-volt battery connected to a resistor with a resistance of 8 ohms. If a current of 3 amperes flows through the resistor for 4 seconds, (a) what is the energy consumed by the circuit, and (b) what is the power consumed by the resistor? The power consumed by the The energy consumed by the resistor is 72 watts. circuit is 288 joules in 4 seconds ELECTRICAL SAFETY  ELECTRICAL SAFETY Electricity presents two known hazards: thermal and shock. A thermal hazard is one in which an excessive electric current causes undesired thermal effects, such as starting a fire in the wall of a house. A shock hazard occurs when an electric current passes through a person. Shocks range in severity from painful, but otherwise harmless, to heart-stopping lethality.  THERMAL HAZARD Electric power causes unwanted heating when electric energy converts to thermal energy faster than it can dissipate. A common example is a short circuit, where worn insulation allows wires to contact, creating a low-resistance path. This can rapidly heat surrounding materials, melt insulation, and potentially cause a fire.  RISKS CAUSED BY THERMAL HAZARDS 1.) Fires - Extreme heat can ignite surrounding materials, resulting in potential fires. 2.) Insulation Damage - Excessive heat may melt wire insulation, leaving live wires exposed. 3.) Burn Injuries - Contact with overheated equipment or wiring can cause burn injuries.  SHOCK HAZARD Electric shock occurs when an external electric current passes through the body, causing a physiological reaction or injury. Currents exceeding 300 mA can be fatal, often leading to ventricular fibrillation, a severely irregular and life-threatening heartbeat. However, in certain cases, an electric shock from a defibrillator can restore a normal heartbeat and save a heart attack victim in fibrillation.  EFFECTS OF AN UNDESIRABLE ELECTRIC SHOCK CAN VARY IN SEVERITY: 1.) A slight sensation at the point of contact 2.) Pain 3.) Loss of voluntary muscle control 4.) Difficulty breathing 5.) Heart fibrillation 6.) And possibly death. The loss of voluntary muscle control can cause the victim to not be able to let go of the source of the current.  SAFETY PRECAUTIONS 1.) Avoid overloading circuits by ensuring they are not overloaded to prevent overheating. 2.) Inspect equipment regularly by checking cables, wires, and connections for signs of wear, damage, or fraying, and avoid using damaged tools or equipment.  SAFETY PRECAUTIONS Use Ground fault circuit interrupters (GCFI)  SAFETY PRECAUTIONS A Ground Fault Circuit Interrupter (GFCI) protects against electric shocks and reduces fire risks by shutting off power when it detects unintended current flow, such as through water or a person. It’s crucial in moisture-prone areas like bathrooms, kitchens, and outdoors, as it reacts within milliseconds to prevent harm. DEVICES FOR MEASURING CIRCUITS AND VOLTAGES DEVICES FOR MEASURING CIRCUITS AND VOLTAGES VOLTMETER A voltmeter is an instrument that measures the difference in electrical potential between two points in an electric circuit. An analog voltmeter moves a pointer across a scale in proportion to the circuit's voltage; a digital voltmeter provides a numerical display. Any measurement that can be converted to voltage can be displayed on a meter that is properly calibrated; such measurements include pressure, temperature, and flow. In order for a voltmeter to measure a device’s voltage, it must be connected in parallel to that device. This is necessary because objects in parallel experience the same potential difference. Voltmeter in Parallel (a) To measure the potential difference in this series circuit, the voltmeter (V) is placed in parallel with the voltage source or either of the resistors. Note that terminal voltage is measured between points a and b. It is not possible to connect the voltmeter directly across the EMF without including its internal resistance, r. Voltmeter in Parallel: (b) A digital voltmeter (DVM) measures an unknown input voltage by converting the voltage to a digital value and then displays the voltage in numeric form. DVMs are usually designed around a special type of analog-to- digital converter called an integrating converter. Applications of Voltmeters: 1.) Voltmeters are essential for identifying voltage issues in electrical circuits, helping to pinpoint faulty components or connections. 2.) Voltmeters are used to ensure the correct voltage output from power supplies, preventing damage to sensitive equipment and ensuring proper operation. 3.) Voltmeters are used to measure battery voltage, helping determine whether the battery is charged, undercharged, or faulty. DEVICES FOR MEASURING CIRCUITS AND VOLTAGES AMMETER An ammeter measures the electric current in a circuit. The name is derived from the name for the SI unit for electric current, amperes (A). It is usually connected in series with the circuit element (or load). So all the current that flows through the load also flows through the ammeter. In order for an ammeter to measure a device's current, it must be connected in series to that device. This is necessary because objects in series experience the same current. They must not be connected to a voltage source—ammeters are designed to work under a minimal burden (which refers to the voltage drop across the ammeter, typically a small fraction of a volt). Ammeter in Series: An ammeter (A) is placed in series to measure current. All of the current in this circuit flows through the meter. The ammeter would have the same reading if located between points d and e or between points f and a, as it does in the position shown. (Note that the script capital E stands for EMF, and r stands for the internal resistance of the source of potential difference.) Applications of Ammeters: 1.) Ammeters are used in the testing and maintenance of electrical equipment, ensuring that the components are operating within the specified current range and preventing overloads. 2.) In both residential and industrial settings, ammeters are used to monitor the current drawn by electrical appliances or machines, aiding in energy management and efficiency.