The student is expected to characterize materials as conductors or insulators based on their electrical properties AND design, construct, and calculate in terms of current through, potential difference across, resistance of, and power used by electric circuit elements connected in both series and parallel combinations.
Conductors are materials with loosely attached electrons, which can drift freely between the atoms. Insulators have structures in which all the electrons are tightly bound to atoms so that little or no current flows.
Electric current is the flow of electric charge through an object or medium. In a solid conductor, such as a metal wire, current is carried by moving electrons. In order for electric current to flow through a circuit, it must have a completely unbroken, closed path of conductive material.
Electric current flows when there is a potential difference applied to the circuit, such as from a battery.
The relationship between voltage and current is fundamental to the operation of any circuit or device. The ratio of voltage to current in a device or circuit is known as the resistance. Many devices and circuits follow Ohm’s Law, which says that voltage is directly proportional to current. This can be expressed by the equation Voltage = Current X Resistance or V = I R.
In electric circuits, power is a function of both current and voltage. Power is equal to the product of current and voltage.
In a series circuit, current can only flow along a single path. To calculate total voltage, voltages are added together in series circuits. To calculate total current, the total voltage is divided by the total resistance. The total resistance is equal to the sum of all resistances.
In a parallel circuit, current can flow along multiple paths. The total voltage is the same across each path. To calculate total current, currents along all paths are added together. The reciprocal of the total resistance is equal to the sum of the reciprocals of all resistances.
Conductors and Insulators
Conductors and insulators are two different types of materials with opposite physical properties. Conductors are materials with loosely attached electrons, which can drift freely between the atoms. Insulators have structures in which all the electrons are tightly bound to atoms so that little or no current flows. There are no absolute conductors or insulators; their properties can vary with environmental conditions.
Closed Electrical Circuit
When you open a computer you can see a motherboard, which is full of electrical circuits. A circuit is a closed loop of conductors through which an electrical current can flow. In order for electricity to flow through the circuit, it must have a completely unbroken, closed path of conductive material. Sometimes we find that an electrical device does not work. One of the possible reasons is that it has a broken path inside. Electricity involves the flow of electric currents in a closed path under the influence of driving voltage and controlled by the load. Two requirements that must be met in order to establish an electric circuit.
Energy Supply to Move Charge from Low to High Potential Energy: There must be an energy supply capable of doing work on a charge to move it from a low energy location to a high energy location and thus establishing an electric potential difference across the two ends of the external circuit.
Closed Loop from Positive Terminal to Negative Terminal: There must be a closed conducting loop in the external circuit that stretches from the high potential, positive terminal, to the low potential, negative terminal.
Note: Ben Franklin envisioned positive charges as the carriers of charge. As such, an early convention for the direction of an electric current was established to be in the direction that positive charges would move. The convention has stuck and is still used today. The direction of an electric current is by convention the direction in which a positive charge would move. Thus, the current in the external circuit is directed away from the positive terminal and toward the negative terminal of the battery. Electrons would actually move through the wires in the opposite direction. Knowing that the actual charge carriers in wires are negatively charged electrons may make this convention seem a bit odd and outdated. Nonetheless, it is the convention that is used worldwide.
There are two ways a circuit can be set up: series or parallel.
Series: A series circuit is a type of circuit in which the electrical current runs through each component and each component handles the same current.
Parallel: A parallel circuit is a type of circuit where the voltage is equal in each branch of the circuit.
Current, Voltage, and Resistance Relationships
The relationship between current, voltage, and resistance in an electrical circuit is fundamental to the operation of any circuit or device and is expressed in Ohm’s Law: Voltage is equal to the product between the electrical current that is passing through and the resistance against the current.
Current: Current is the flow of an electrical charge through an object or medium. Potential difference is the amount of energy needed to move a charged particle from one point to another in an electrical field. Current flows from high potential energy to low potential energy. Current is denoted by “I” and is measured in amperes (A). The origin of “I” is “intensit”, the French word for “current”, as Ampre was French.
Voltage: Electric potential is the potential energy per unit charge, and depends only on the location of the charge within the electric field. Voltage is the difference in electrical potential between two points. The voltage is equal to the product of the current and the resistance. Electrical potential difference (voltage) is denoted by “V” and is measured in volts (V).
Resistance: Resistance is a measurement of how an object opposes the flow of electric current through it. A resistor is an electrical component that provides electrical resistance in a circuit. When a charge falls through a potential difference, it dissipates energy. Power is the rate at which this energy is transferred and passed through. Resistance is denoted by “R” and is measured in ohms (Ω). Equivalent resistance is the total resistance in a circuit or part of a circuit, and it is used to simplify the electrical schematic.
Total Resistance in Series Circuits: Voltages are added together in series circuits. Thus in a series circuit, the resistances of all the components are summed together.
Total Resistance in Parallel Circuits: Currents are added together in parallel circuits. So in a parallel circuit, the reciprocals of the resistances are summed.
Electrical System Protection
The protection of an electrical system is one of the priority factors. Fuses are widely used to accomplish this. A fuse is a device applied in an electrical circuit to protect the circuit against excess current. A Ground Fault Interrupter (GFI) is a device that disconnects a circuit when it senses that the electrical current passing through it is not balanced between the energized conductor and the return neutral conductor. It can also be called as Residual Current Circuit Breaker (RCCB).