Energy And Voltage In Circuits
Visão Geral
Every electrical device you use, from a phone charger to a hospital ventilator, relies on charges moving through circuits and transferring energy along the way. Understanding how current, voltage and resistance relate to each other is the key to predicting what any circuit will do, and it is one of the most heavily examined areas of your Edexcel course.
You will learn the equations that connect charge, current and time, explore how voltage measures energy transfer per coulomb, and master Ohm's law. You will also discover how different components behave, from resistors that obey a straight-line rule to diodes that only conduct one way, and see why homes use parallel circuits while fairy lights use series.
Objetivos
- Explain why a series or parallel circuit is more appropriate for particular applications, including domestic lighting
- Understand how the current in a series circuit depends on the applied voltage and the number and nature of other components
- Describe how current varies with voltage in wires, resistors, metal filament lamps and diodes, and how to investigate this experimentally
- Describe the qualitative effect of changing resistance on the current in a circuit
- Describe the qualitative variation of resistance of light-dependent resistors (LDRs) with illumination and thermistors with temperature
- Know that lamps and LEDs can be used to indicate the presence of a current in a circuit
- Know and use the relationship between voltage, current and resistance: voltage = current x resistance, V = I x R
- Know that current is the rate of flow of charge
- Know and use the relationship between charge, current and time: charge = current x time, Q = I x t
- Know that electric current in solid metallic conductors is a flow of negatively charged electrons
- Understand why current is conserved at a junction in a circuit
- Know that the voltage across two components connected in parallel is the same
- Calculate the currents, voltages and resistances of two resistive components connected in a series circuit
- Know that voltage is the energy transferred per unit charge passed and that the volt is a joule per coulomb
- Know and use the relationship between energy transferred, charge and voltage: energy transferred = charge x voltage, E = Q x V
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- What does electric current measure? A) The energy stored in a battery B) The rate of flow of charge C) The resistance of a wire D) The voltage across a component Answer: B
- A charge of 60 C passes through a lamp in 20 s. What is the current? A) 1200 A B) 80 A C) 3 A D) 0.33 A Answer: C
- Which I-V graph is a straight line through the origin? A) Filament lamp B) Diode C) Fixed resistor D) Thermistor Answer: C
- In a parallel circuit, what happens to the voltage across each branch? A) It is shared equally B) It is the same as the supply voltage C) It decreases along each branch D) It depends on the current Answer: B
- What happens to the resistance of a thermistor as temperature increases? A) It increases B) It decreases C) It stays the same D) It drops to zero Answer: B
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Ohm’s Law: Resistance and Simple Circuits
What drives current? We can think of various devices—such as batteries, generators, wall outlets, and so on—which are necessary to maintain a current. All such devices create a potential difference and are loosely referred to as voltage sources. When a voltage source is connected to a conductor, it
"College Physics: Ohm’s Law: Resistance and Simple Circuits" by OpenStax, OpenStax, Rice University, licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Source: https://openstax.org/books/college-physics/pages/20-2-ohms-law-resistance-and-simple-circuits. Access for free at https://openstax.org/books/college-physics/pages/1-introduction
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Resistors in Series and Parallel
Most circuits have more than one component, called a resistor that limits the flow of charge in the circuit. A measure of this limit on charge flow is called resistance . The simplest combinations of resistors are the series and parallel connections illustrated in Figure 21.2 . The total resistance
"College Physics: Resistors in Series and Parallel" by OpenStax, OpenStax, Rice University, licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Source: https://openstax.org/books/college-physics/pages/21-1-resistors-in-series-and-parallel. Access for free at https://openstax.org/books/college-physics/pages/1-introduction
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