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Electricity Electric Charge Positive and Negative Charge • Atoms – Protons (+) – Inside nucleus – Neutron (0) – Inside nucleus – Electron (-) – Outside Nucleus • Static Electricity – excess electric charge • Law of conservation of charge – charge can be transferred but can not be created of destroyed Electric Charge Positive and Negative Charge • Opposite charges attract • Like charges repel • Electric fields surround every electric charge, this exerts a force that causes other electric charges to repel or attract. Electric Charge Insulator and Conductors • Conductors – Electrons are able to move • Example – metal is a good conductor • Insulators – Electrons don’t move • Example – plastic, rubber, wood and glass Electric Charge Charging Objects • 2 material rub together they transfer electrons – One = positive – The other = negative – This is called “charging by contact” Electric Charge Charging Objects • Charging by induction – rearrangement of electrons on a neutral object caused by a nearby object • Lightning – large static discharge • Thunder – hot air in lightning bolt path expands rapidly, producing sound waves • Ground – connecting an object to earth with a good conductor Detecting an electric charge • Electroscope – detects electric charge – No charge = straight down – Charge touches rod…both ends negatively charged = repel Current and Voltage Difference • Electric Current – net movement of electric charges in a single direction. – Electric Current – Measure in Amps • 1 amp = 6,250 million billion electrons flowing past a point every second Current and Voltage Difference • Voltage Difference – force that causes electric charge to flow – Measured in volts Current and Voltage difference • Circuit – closed path that an electric current follows. – If circuit is broken (open) current will not flow. Batteries • Purpose – provides the voltage difference that is needed to keep electric current flowing Batteries • Dry Cell – Chemical reactions in the paste transfer electron to the zinc container Batteries • Wet Cell Battery – Made of different metals of metallic compounds in a conducting solution. Contain many wet cells together Battery • Lead Acid Battery – Series of six wet cells made up of lead and lead dioxide plates in a sulfuric acid solution. Resistance • Resistance – tendency of material to oppose the flow of electrons, changing electrical energy into thermal energy and light Current in a simple circuit • Contains a source of voltage difference (battery) a device that has resistance (light bulb) and conductors that connect the device to the battery terminals. Current in a simple circuit • Ohm’s Law – current in a circuit equals the voltage difference divided by the resistance • I = V/R • Current = voltage difference / resistance – Current – Amps – Voltage Diff – Volts – Resistance - Ohms Series Circuits • Current has only one loop to flow through – Flash lights and some holiday lights • Open circuit – when any part of the circuit is disconnected no current flows through the circuit Parallel Circuits • Contain two or more branches for current to move through • Advantages – when one branch is opened (turn off a light) the current flows through the other branches Household Circuits • Parallel Circuits • In a house many appliances draw from the same circuit. More appliances = more heat – Fuse – current becomes too high small piece of metal melts causes a break in the circuit. – Circuit breaker – current gets to high, a small piece of metal bends and opens the circuit, can usually be reset by pushing it back to on position. Electrical Power • Electrical Power – rate at which electricity is converted into another form of energy – Appliances with electric heating elements (ovens, hair dryers, ovens) use more electrical power that other appliances. Electrical Power • Calculating electrical power – depends on the coltage difference and current • Electrical Power = current(Amp) X Volatage diff. (volts) Unit for power = watts KW = 1,000 watts Electrical Power • Electrical Energy = kWh • kWh = electrical power(kW) X Time(hrs)