Electrical circuits

• Electricity - electrical energy; a type of energy fuelled by the transfer of electrons from negative to positive points within a conductor
• electrical charge (Q) - the physical property of matter that causes it to experience a force when placed in an electromagnetic field

  • electrons are the charge carriers that flow in an electrical circuit from the negative to positive terminals
  • units: Coulombs (C)
• current (I) - rate of flow of electric charge

  • units: Amperes (A)
  • flows from positive to negative
• voltage (V)  - energy applied per unit charge

  • units: Volts (V) ; Joules/Coulomb
• • voltage divider - a simple circuit which turns a large voltage into a smaller one
• • simplest voltage divider: two resistors are placed in series across the batter
  • used to change the potential difference across one component so that a lower voltage can be used in another part of the circuit
• Types of Electrical Circuits:

  series - exactly one electrical path

  parallel - all components are connected across from each other, forming exactly two sets of electrically common points
• Series and Parallel circuits

  
• Resistance:

  • the measure of the degree to which a conductor opposes an electric current through that conductor
  • units: ohms
  • R = pL/A
• Ohm’s Law

  • the potential difference across an ideal conductor is proportional to the current through it
  • I = V/R
• • ohmic resistors - constant resistance
  • they follow Ohm’s law
  • the only ohmic resistor is a straight wire 
  • non-ohmic resistors give a curve with an increasing gradient
  • resistance increases as current increases
• • diodes - only allows current to flow in one direction
  • if it flows the other direction, no current is allow through the diode
  • forward bias = positive to positive (on state) 
  • reverse bias = positive to negative (off state)
  • used in LDRs and thermistors
• Superconductors

  • a material that can conduct electricity with no resistance once they are cooled to a temperature called the transition temperature (TcTc​) 
  • at the transition temperature, the resistance suddenly drops to zero
  • less power loss
• Capacitors

  • an electrical component used to store energy electrostatically in an electric field
  • contains two electrical conductors (plates) separated by a dielectric (insulator)
• Static Electricity 

  • two objects are rubbed together
  • one object gives up electrons and becomes more positively charged while the other material collects electrons and becomes more negatively charged
  • one material has a weakly bound electrons and the other has many vacancies in its outer shells
• Making Magnets:

  • stroking method - by stoking a bar of steel with a bar magnet, the domains become aligned and a north and south pole are induced
  • electrical method - placing a bar of steel or iron in a coil of wire (solenoid) and passing DC current through the wire
• types of magnetic materials

  • hard magnetic materials - difficult to magnetize but do not readily lose their magnetism
  • soft magnetic materials - easy to magnetize but easily lose magnetic property
• A Fuse is an electrical safety device that protects the circuit from short-circuiting, the fuse wire is made of tin alloys that have high resistance and low melting points
• A cell is a single unit of device that converts chemical energy into electrical energy. A battery is a collection of cells that converts chemical energy into electrical energy.
• An electrical cell is an "electrical power supply". It converts stored chemical energy into electrical potential energy, allowing positive charges to flow from the positive terminal to the negative one through an external circuit.
• A voltmeter is an instrument used to measure voltage. Its other main purpose is to measure the electrical potential difference between two separate points in an electrical circuit
• In a circuit, the battery is the main source of energy that provides a voltage which allows the current to flow through.
• An ammeter is an instrument used to measure the current in a circuit. Electric currents are measured in amperes (A)
• A resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit. Resistors can also be used to provide a specific voltage for an active device such as a transistor.
• The main use of a thermistor is to measure the temperature of a device. With this property, they are used as overcurrent protection devices.

  When an excessively large current flows, they generate heat by themselves and become highly resistive
• Variable resistors are widely used in electric circuits to adjust the value of current or voltage, since the resistance of variable resistors can be set to a certain value. Variable resistors allow you to adjust the value of voltage by changing the resistance and keeping current constant
• The Light Dependent Resistor (LDR) Sensor is a basic tool that senses how much light is around. LDR working by responding to different wavelengths of visible and infrared radiation, with its resistance decreasing as the amount of ambient light intensity increases.
• EDs (Light Emitting Diodes) convert electrical energy directly into light, delivering efficient light generation with little-wasted electricity.
• The buzzer is an electronic device that makes an audible sound when an external voltage is applied. 
• an inductor's role is to prevent sudden changes in current used.
• The ground wire serves as a secure route for electrical currents in case of a short circuit. If a short circuit occurs, the ground wire will trigger the circuit breaker or fuse, offering a much safer alternative to the hazardous electrical shock that would otherwise occur.