Electricity Transmission & DistributionOxford AQA IGCSE Physics: Flashcards

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What is the National Grid?

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What is the National Grid?: The network of transmission cables and transformers that distributes electricity from power stations to consumers.
Why is electricity transmitted at high voltage?: It reduces the current for a given power, which reduces energy losses due to heating in the cables, making transmission more efficient.
What are the two main parts of a transformer, and what are they wound on?: A primary coil and a secondary coil, both wound on a soft iron core.
Why do transformers only work with alternating current?: AC creates a changing magnetic field in the core, which is needed to induce a pd in the secondary coil; dc does not change, so no pd is induced.
What is a step-up transformer?: A transformer where the secondary potential difference is greater than the primary potential difference.
What is a step-down transformer?: A transformer where the secondary potential difference is less than the primary potential difference.
State the transformer equation.: Vp / Vs = np / ns.
State the power equation for an ideal (100% efficient) transformer.: Vp × Ip = Vs × Is.
What frequency range do switch mode transformers operate at?: 50 kHz to 200 kHz.
Give two advantages of switch mode transformers over traditional transformers.: They are much lighter and smaller, and use very little power when on with no load applied.
Give an example device that uses a switch mode transformer.: A mobile phone charger.
A step-up transformer has 50 primary turns and 500 secondary turns, with 12 V on the primary. What is the secondary pd?: Vs = Vp × (ns/np) = 12 × (500/50) = 120 V.