Electrical current is the flow of electrons. The amount of charge carried by a current of: 1A flowing for 1s = 1 coulomb.- charge (C) = current (A) x time (s)
Electrical energy is transformed to heatenergy when charge flows through the resistor.--------------------- energy transformed (J) = potential difference (V) x change (C)
A potential difference (voltage)exerts a force that pushesfree electrons along.
Electricalresistance in wires due to free electronscolliding with fixed, positive ions and their bound electrons.
Resistance in wires depend on their length, thickness, temperature and type of material.
Metals have free electrons and are good conductors with low resistances.
Insultators do not have free electrons and so are poor conductors with very high resistances.
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Circuits and resistance 2
Ohm's Law states that: resistance(Ω) = potential difference/current (A)
The resistance of: a light-dependant resistor (LDR) decreases as light intensity increases,a thermistor decreases as the temperature increases,a filament lamp increases as the temperature of the filament increases.
Components in an electricalcircuit can be connected in the series and in parallel.
In a series circuit:current through all components in the same at all points; total p.d. is shared between all components; total resistance = sum of resistances of components.
In parallel circuit: total current is the sum of currents through the seperatecomponents; the p.d. across all components is the same.
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Domestic electricity
UK domestic electricity is an alternating current of frenquency 50Hz, average p.d. 230V. An oscilloscopeshows the p.d. and frenquency of a.c and d.c.
Fuses, circuit breakers and earth wiresprotect appliances from damage and people from injury or death. Three-pin plugs must be correctly wired and hold the correct fuse.
The current through an appliance and the size of the fuse required can be calculated from: power (W) = current (A) x p.d. (V)
The rate of which energy is transformed is called power: power (W) = energy transformed (J) / time taken (s)
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Radioactive substances
Different forms of an element with the same number of protons but with a different number of neutrons in their atoms are called isotopes.
Isoptopes have the sameatomic number but different mass number.
Isotopes with unstable nucleiemitenergy ----> as particles or rays called radiation.
A beta particle is a high energy electron.
A gamma ray is an electromagnetic wave with no charge or mass.
Background radiation comes mainly from rocks, soil, cosmetic rays, living things and medical X-rays.
Using scattering experiments, Rutherford and Marsdenrevealed the structure of an atom: a small dense nucleus of protons and neutrons (held together by strong nuclear forces); fast moving electronsorbiting round the nucleus; and lots of empty space.
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Nuclear fusion and nuclear fission
Nuclear fission = is the splitting of a nucleus.
Neautrons are fired at unstable isotopes and energy is released. This produces more neautrons and sets up a chain reaction.
Nuclear Fusion = two small nuclei join together to form a larger one, as happens in stars: 2 hydrogen nuclei --> 1 helium nucleus + ENERGY
Uranium-235 and plutonium-239 are fissionableelements and are used to ----> producenuclear energy in nuclear power stations.
The minimum amount of pure uranium-235 needed to produce large amounts of energy is called critical mass.
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