Electricity

• Electricity is a subject that is specific for a QA.
• Three quantities that are really interested in are V, I, and R.
• In a resistor, there might be a current which is the rate of flow of charge particles.
• Current is represented by the symbol I.
• The intensity of current is measured in amps.
• Time is represented by the symbol t.
• Electrons are often used as the charge carriers in electrical circuits.
• Potential difference is the energy transferred within a component.
• In a parallel circuit, the current is split at a junction and shared, this is called a potential divider circuit.
• The total resistance of a series circuit is the sum of all the individual resistors.
• Around any closed loop in the circuit, the sum of the EMFs is equal to the sum of the potential differences.
• In a series circuit, the current is the same everywhere due to the conservation of charge.
• The total resistance of a parallel circuit is equal to one over the sum of all the individual resistors.
• Potential difference is defined as a work done per unit charge.
• EMF is the energy transferred to the circuit by a battery or cell.
• Charge in equals charge out, current in equals current out, the sum of the EMFs equals some of the potential differences, V is equal to I times R, P is equal to I times V, P is equal to V squared over R, P equals e over T, and P equals IV.
• There are two main types of circuit: series and parallel.
• Potential divider circuits can also be represented as a long resistor, with the potential difference between two points within the resistor represented as an arrow pointing to that point.
• Potential divider circuits can be used for sensing, where an external change causes a change in one of the components, affecting how much potential difference is across it.
• Conventional current in a DC circuit goes from positive to negative, but the actual particles moving are electrons which are moving from the negative side and being attracted towards the positive end of the terminal.
• Potential divider circuits divide the potential difference between the two resistors, and the total energy transferred by a component equals IV.
• Power is the rate of energy transfer, and the total energy transferred by a component equals IV.
• The current-voltage (IV) characteristics for a resistor are represented by a straight line going through the origin.
• The arrow in a potential divider circuit can point in either direction, indicating that the potential difference can be positive or negative.
• The resistance of a piece of wire depends upon the length and is proportional to the length but inversely proportional to the cross-sectional area, with the constant of proportionality being Rho.
• The current-voltage (IV) characteristics for a filament lamp are represented by a curve that is not a straight line going through the origin.
• As a solid gets hotter, the lattice vibrates more and it's harder for the electrons to move through, resulting in a higher resistance.
• The resistivity of a wire depends on the temperature and increases as the temperature increases.
• When a solid is quite cool, the lattice is vibrating and it's easy for the charge carriers to move through, resulting in a relatively low resistance.
• In a good conductor, there are many free electrons which are delocalized from the positive metal ions.
• The current-voltage (IV) characteristics of a component or effectively divides the potential using this component.
• The area of a wire is equal to PI d squared divided by 4, where d is the diameter measured using a micrometer.
• Semi conductors can be thought of as having electrons which are bonded to the material and when it gets hotter, there's enough energy for these electrons to move out of that material, resulting in a decrease in resistance as the temperature increases.
• The current-voltage (IV) characteristics for a diode allow the current to flow in one direction but not the other, with a very low resistance in one direction and a high resistance in the other.
• Superconductivity occurs at a critical temperature below which the resistance falls to zero.
• Thermistors are thermal resistors and their resistance decreases as the temperature increases.
• Potential difference, represented by the symbol V, is the difference in the electrical potential between two points and is equal to the energy transferred per unit charge.
• Potential divider circuits can use the full range of potential differences available.
• Cells in series add their internal resistances, while cells in parallel decrease the effect of their internal resistances.
• Resistance is defined as the ratio of the potential difference across a component divided by the current in that component and is measured in ohms.