2. Electricity

• Electric current is defined as the rate of flow of charge 
• Current flows from the positive terminal to the negative terminal of a cell
• A circuit consists of two or more components connected together by conductors, such as wires.
• In series circuits, all components are connected end-to-end with no branches.
• an ammeter is a meter for measuring electric current in amperes (A)
• an ampere is the SI unit of electric current
• a battery is two or more electrical cells connected together in series; the word may also be sued to mean a single cell
• biomass fuel is a renewable energy source that is made from living things and can be used to generate electricity
• a circuit breaker is a safety device that automatically switches off a circuit when the current becomes too high
• current is the rate at which electric charge passes a point in a circuit
• a diode is an electrical component that allows electric current to flow in only one direction
• direct current is electric current that flows in the same direction all the time
• an appliance earthed when the case of an electrical appliance is connected to the earth wire (for safety)
• electrical field is a region of space in which an electric charge will feel a force
• thick cables reduce heat loss as there is less resistance
• transmitting electricity at high voltages reduces the energy that is lost as heat due to the resistance of the cables
• current is the rate of flow of charge
• resistance is the opposition is the flow of current
• voltage is the energy transferred per unit charge
• positive to negative is a conventional current
• conventional current is the current that flows in a circuit when a potential difference is applied across it
• current is the same everywhere in a series circuit
• bulbs are dimmer in a series circuit as voltage is shared between bulbs
• bulbs are brighter in a parallel circuit as there is equal voltage between bulbs
• greater voltage -> greater current
• when temperature increases there is more resistance. there is more kinetic energy meaning more collisions. it is harder for electrons to flow as there is no clear path
• metals like copper, iron, gold, aluminum, and silver are the best materials for conducting electricity
• plastic, wood, glass, and rubber are electrical insulators
• When certain insulating materials are rubbed against each other they become electrically charged. This is called charging by friction
• The charges remain on the insulators and cannot immediately flow away. One becomes positive and the other negative
• An example of this is a plastic or polythene rod being charged by rubbing it with a cloth. Both the rod and cloth are insulating materials
• This occurs because negatively charged electrons are transferred from one material to the other. The material, in this case, the rod, gains electrons
• Since electrons are negatively charged, the rod becomes negatively charged. As a result, the cloth has lost electrons and therefore is left with an equal positive charge
• Electrons are negatively charged particles, whilst protons are positive and neutrons are neutral
• All objects are initially electrically neutral, meaning the negative (electrons) and positive charges are evenly distributed
• Photocopiers use static electricity to copy paper documents, most commonly in black and white
• An image of the document is projected onto a positively charged copying plate. The plate loses its charge in the light areas and keeps the positive charge in the dark areas (i.e the text)
• A negatively charged black toner powder is applied to the plate and sticks to the part where there is a positive charge. The toner is then transferred onto a new blank sheet of white paper
• The paper is heated to make sure the powder sticks (hence why photocopied paper feels warm). The photocopy of the document is now made. Inkjet printers work in a similar way, but instead of the black toner powder, a small jet of coloured ink is negatively charged and attracted to the correct place on the page
• Insecticides are chemicals used to kill pests in order to protect crops. In order to spray crops effectively whilst using a minimal amount of chemicals, the sprayer has to deliver the chemicals as a fine mist and cover a large area