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**Generating Electricity**

To generate a voltage (electricity) you need: a magnetic field a conductor movement V The size of the voltage induced depends on: strength of the magnets (magnetic field) the length of coiled wire (conductor) speed of movement

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The Dynamo coil As the dynamo is turned, the magnet rotates beside the coil of wire. An A.C voltage is generated in the coils Power station generators are much bigger and use electromagnets. electrical output rotating magnet

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**(rotating electromagnets)**

STATOR (stationary coils of wire) ROTOR (rotating electromagnets) Generator turbine shaft Turbine Blades

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**M.A.R.S Floating Wind Powered Generator**

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Info Speaking of R2-D2, this M.A.R.S. Floating Wind Generator looks a lot like a flying R2 droid on its side. This helium-filled, horizontal-rotating M.A.R.S. (Magenn Power Air Rotor System) will go into production with its 4.0 kw unit this year with 7 more models planned for release in the next 4 years. The 2010 and 2011 planned models will be able to power a small town on their own. The generated electrical energy travels town its 1000-foot tether rope, with the energy available for immediate use. With its helium, balloon-like flying system, M.A.R.S. can fly higher than other wind turbines, able to reach altitudes with much higher wind speeds.

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Size of Voltage Experiment dynamo oscilloscope

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**greater amplitude (bigger voltage) higher frequency (faster rotation)**

Results slow speed high speed greater amplitude (bigger voltage) higher frequency (faster rotation)

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**transformers require an AC voltage**

A transformer consists of 2 coils of wire and iron core which passes through both coils. iron core primary coil secondary coil transformers require an AC voltage

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**secondary voltage (VS)**

The circuit symbol for a transformer is: An AC voltage in the primary coil induces (creates) a voltage in the secondary coil. The size of the secondary voltage depends on: size of primary voltage number of turns on each coil. NP VP VS NS Quantity Unit secondary voltage (VS) primary voltage (VP) secondary turns (NS) primary turns (NP) volts (V) ** NO UNIT **

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**This is a STEP DOWN transformer**

Example 1 Calculate the secondary voltage for the transformer shown. 1000 T 230 V AC VS 52 T This is a STEP DOWN transformer

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**This is a STEP UP transformer**

Example 2 Calculate the secondary voltage for the transformer shown. 300 T 50 V AC VS 12,000 T This is a STEP UP transformer

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**Current in Transformers**

NP IP NS IS

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**Calculate the current in the secondary coil.**

Example 1 Calculate the current in the secondary coil. 0.1 A IS 1000 T 50 T

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**Calculate the voltage and the current in the secondary coil.**

Example 2 Calculate the voltage and the current in the secondary coil. 0.05 A IS 230 V VS 10,000 T 500 T Voltage

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Current

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**Transformer Power & Efficiency**

If the transformer is 100% efficient: To calculate power we use So this gives us the formula ** NOT on data sheet **

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Example 1 Calculate the current in the secondary coil, assuming the transformer is 100% efficient. 0.04 A IS 50 V 12 V

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Example 2 Calculate the current in the secondary coil, assuming the transformer is 90% efficient. 0.08 A IS 230 V 12 V Power in Primary Power in Primary

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Power in Secondary Current in Secondary

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**step-down transformer**

Power Lines Electricity is provided by power lines called The National Grid. 400,000 V 230 V 25,000 V step-up transformer step-down transformer The output voltage is stepped up to reduce power loss in the wires of the national grid.

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**Stepping up the voltage reduces the size of the current.**

Smaller current, less power loss. Example 1 A transmission power line of length 60km has a resistance of 2 Ω per kilometre. The total current in the cable is 50 A. Calculate the power loss in the transmission line.

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Practice Problems A horizontal wire is moving vertically upwards in a horizontal magnetic field of strength 0.150 tesla which is perpendicular to the.

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