AQA GCSE Physics Further electricity
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If an atom loses an electron, it will become positively charged, since there will be more protons than electrons. If an atom gains an electron, it will become negatively charged, since there will be more electrons than protos. These charged particles are called ions and they will exert non-contact electrostatic forces of static electricity on other charged objects. Oppositely charged objects will attract each other, whereas like charges will repel each other. When insulating materials are rubbed together, they may become electrically charged as electrons are rubbed off from one material to another. Since insulators will prevent electrons from moving between the materials, the charge formed is static.
Charged objects have an electric field around them. Electric fields are regions in which charges experience an electrostatic force. In electric fields, arrows will point from positive to negative, showing the direction in which a positive charge will experience a force. Electric fields with arrows that are closer together will be stronger, and thus the electrostatic forces they will exert will be stronger. Around a point charge, the electric field will be a radial field. The field between two parallel plates is called a uniform field. A strong enough electric field may force charges to move through insulators, which will result in sparking.
The Law of conservation of charge states that, for an isolated system, the net charge will remain constant. This is because, whenever a charge is created, an equal and opposite charge is created simultaneously. The Law of conservation of energy states that energy cannot be created or destroyed, but can only be converted from one form to another.
The electromotive force of a cell, emf, ε, is the energy per unit charge converted into electrical energy by the cell and is measured in Volts. The terminal potential difference is the potential difference between the two ends of a cell in a closed circuit. The internal resistance of the cell opposes the charge that flows through it, therefore some of the energy converted by the cell will be used up to overcome this resistance. The following relationship can be constructed for the cell of a closed circuit: ε = V + Ir.
Capacitors are used to store charge and energy. They are made up of two parallel conducting plates separated by an insulator. When connected to a cell, charge flows from the negative terminal to one of the plates and from the other plate to the positive terminal until the voltage across the capacitor is equal to that across the cell. The plates of the capacitor will always have equal and opposite charge and no charge will flow between the plates, thus storing charge. Capacitance is the ability to store electrical energy and is calculated in Farads (F) using the following formula: Capacitance = Charge//Voltage. Since energy is used to charge capacitators, they store energy. The amount of energy stored by capacitators can be calculated using the following formula: E = (1/2)QV = (1/2)CV².
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