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Year 8 Science: Electricity
Transcript of Year 8 Science: Electricity
You have to ‘break’ the circuit to insert a new component in a series circuit. Make or Break? To ‘make’ or ‘close’ a circuit is join all of the metal contacts so the current can flow around the circuit.
To ‘break’ or ‘open’ a circuit is disconnect part of the circuit so that no current can flow.
A switch is used to make or break a circuit easily, but you can do it by connecting or disconnecting wires as well. There are a few symbols and terms that are useful to know to describe circuits. Electric Circuit Basics Parallel The components in a parallel circuit are side by side.
You don’t need to break a circuit to add components in parallel Variations and other symbols you might see around. ? ? ? ? ? ? More Symbols Household One big parallel circuit 240 Volts! Batteries: Direct Current (DC) AC/DC Power stations: Alternating Current (AC) 50 Hertz = 50 cycles per second! Easier to generate and transmit Some simple motors need AC Chemical reaction provides electrical energy Wet Cell Wet = liquid reaction separates charges Some reactions can be reversed... Dry Cell Dry = dry chemical paste instead of liquid Often Connected like this... why? Photovoltaic Energy from sun moves electrons AKA: Solar cell -> electricity Cell Battery Recycling Dangerous heavy metals DO NOT throw old car batteries into trash Look up collection / recycling programs near you Batteries can be recycled!! Power 1) Write an aim PRAC:
Conductor or Insulator? 4) Question: Why is the word 'suspected' used above? Conductors and Insulators Conductors: Allow current to flow easily Insulators: Do not allow current to flow Conductors Outer electrons free to move Metals Like Copper Very common: nice and cheap! Aluminium Expensive but lightweight Insulators Electrons tightly held immobile Non-metallic solids Like Rubber Wood Plastic ? Energy Users Tungsten High resistance metals: Take energy from electrons energy -> light (and heat) Nichrome energy -> heat (and light) Copper wires have very little resistance... Short circuit Without resistance a very large current will flow... Why is this dangerous? Mains power Battery Light globe 3) Make a list of suspected conductors
and suspected insulators 2) Test materials Tree is wet from the rain!
Liquids can be conductors too. Why? + - The more resistance in a circuit the less current in the circuit Current the same Voltage is split Series Circuit Voltage is the same Current is split Parallel Circuit Homework Switches a) Both globes, with both either on or off at the same time?
b) One globe only, with the other on all the time? Switches a) Both globes, with one globe on when the other is off and visa-versa? Most current will go the easiest way More Complex Circuits Current and Voltage in Series and Parallel 6 Current the same Voltage is split Series Circuit Voltage is the same Current is split Parallel Circuit Remember: Filament Switches! (FYI only) SPST = Single Pole, Single Throw SPDT = Single Pole, Double Throw DPST = Double Pole, Single Throw DPDT = Double Pole, Double Throw You can now do questions: 7.3 : 1-7 and 17-29 From the text book 7.2 : ALL