Unit 3 - Electric Circuits PDF

08/07/2024 Topic 2: Magnetism & Electricity Unit 1: Magnetism Unit 2: Electrostatics Unit 3: Electric Circuits Unit 3 1 2 3 4 1...

08/07/2024 Topic 2: Magnetism & Electricity Unit 1: Magnetism Unit 2: Electrostatics Unit 3: Electric Circuits Unit 3 1 2 3 4 1  08/07/2024 Electrical Circuit: A continuous conducting path along which a current can flow. Conventional current direction is ALWAYS from POSITIVE TO NEGATIVE. A circuit will always include a variety of components, which convert the electrical energy carried by the current into other forms of energy such as heat, light or sound. The electrons in the circuit will still travel from NEGATIVE TO Current is not used up, but rather energy is transferred. POSTIVE. 5 6 Before charges can flow in a circuit, the following must be met: 1. The circuit must be “closed”. 2. The charges must have energy to be able to move. Electrical Current (symbol: I): The flow of electrical charge through a current carrying conductor. This means that current is a measure of the number of coulombs of charge that flow past a specific point in the circuit every second. The S.I. unit for current is Ampere (A). 7 8 2  08/07/2024 Current is measured using an Ammeter. An ammeter is always connected in series and thus has a very low resistance so that it does not decrease the current which is being measured. 9 10 Electromotive Force (EMF): Equivalent to the potential Voltage (symbol: V): One volt is the p.d. between two points difference across the terminal of a batter/cell when there is no when one coulomb of electrical charge passing these two points, current present in the circuit. producing one joule of work. Potential Difference (p.d.): The voltage measured across the terminals of a battery/cell when there is current flowing through the circuit. Both EMF and p.d. are measured using Volts (V). 11 12 3  08/07/2024 Both EMF and p.d. are measured using a Voltmeter. A volt meter is always connected in parallel. If there is current flowing through the voltmeter, it will affect our results for current. How do we avoid this? A voltmeter must have incredibly high resistance. This ensures that no current will pass through it. Keeping our results accurate. 13 14 Resistance: Electrical resistance is the ability of a The resistance of a conductor is dependent on four factors: conductor to resist, or oppose, the flow of electrical current through it. 1. Length – The longer the resistor, the greater the resistance. All electrical components have some form of resistance. This makes the electrons lose some electrical energy 2. Thinness – The greater the thickness, the less resistance. which they carry. This can be both desirable and undesirable, depending 3. Temperature – The greater the temperature, the greater the on what we want out of the circuit and the present resistance. resistance. A bulb has a very high resistance, and is able to convert 4. Type of material used – Different materials offer different levels of that electrical energy into heat and light energy. resistance, with different uses as well. Resistor: A component of an electrical circuit which is used for it electrical resistance. This reduces the danger of circuits overheating, but is also used to convert the electrical energy into other useful forms of energy. 15 16 4  08/07/2024 17 18 German physicist who discovered the law, named Ohm’s Law: The ratio of the potential difference across a conductor after him, which states that the current flow through a conductor is directly proportional to the and the electric current flowing through it is constant (resistance), potential difference (voltage) and inversely provided that the temperature remains unchanged. The current which proportional to the resistance. flows through a conductor is directly proportional to the potential While his work greatly influenced the theory and difference (voltage) and inversely proportional to the resistance. applications of current electricity, it was so coldly received that Ohm resigned his post at Cologne. He accepted a position at the Polytechnic School of Nürnberg in 1833. Finally his work began to be recognized; in 1841 he was awarded the Copley Medal of the Royal Society of London and was made a foreign member a year later. The ohm, the physical unit measuring electrical resistance, also was named for him. 19 20 5  08/07/2024 When the charge moves through a resistor, it collides with other charges and the nuclei of the substance (resistor). These collisions cause kinetic energy, which is then used or converted into light or sound. Eg. A light bulb with a burning filament. When the resistance increases, the current struggles to go through that resistor, decreasing the current. We would need more voltage to counteract the increase in resistance if we want the same result from the resistor. Ohm (symbol 𝜴): The resistance of a conductor in which a current of one ampere flows when a potential difference of one volt is applied across its ends. 21 22 Not all conductors obey Ohm’s law. Recall what Ohm’s law states, the ratio of voltage and current is constant, provided that the temperature remains the same. Sometimes, a resistor does heat up, and the temperatures does change. When the temperature increases, it becomes more difficult for the electrons to flow through the resistor. 23 24 6  08/07/2024 Resistors in series have a total combined resistance (R) which is equal to the sum of all the resistors in the series circuit. 25 26 Resistors in parallel have a total combines resistance (R), which is found using the following equation 27 28 7  08/07/2024 References Britannica, T. Editors of Encyclopaedia (2022, July 2). Georg Ohm. Encyclopedia Britannica. https://www.britannica.com/biography/Georg-Ohm 29 30 8