CORE Physics (Short Course) - 9223 OxfordAQA

Electricity Transmission And Distribution

Muhtasari

The cables slung between pylons across open country are thinner than most people expect, and they are carrying the output of an entire power station. They manage it because the potential difference across them is enormous and the current in them is small, and that trade is the single decision on which the whole national supply rests. Get it wrong and a useful fraction of everything a station produces would be wasted warming up the countryside before it reached a single house.

This lesson follows the energy along that route, from the station to the socket, and asks you to be able to name every part of it in order. You will meet the two kinds of transformer that sit at the ends of the transmission line, one raising the voltage for the journey and one lowering it again so that what arrives in a street is safe to bring indoors. Then you will do the arithmetic that shows exactly how much is saved by sending the energy at hundreds of thousands of volts, using two equations you already have on the sheet at the back of your paper.

Malengo

  1. Electricity is distributed from power stations to consumers along transmission cables with transformers at both ends. Students should be able to identify and label the essential parts of an electric power transmission and distribution system.
  2. For a given power rating, a high distribution voltage reduces the current flowing, therefore reducing energy losses due to heating and making the system more efficient.
  3. Step-up and step-down transformers are used to increase the voltage before the distribution lines and reduce it at the end to produce a safer voltage for local consumers.

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Maelezo ya Somo

Stand under a line of pylons on a quiet day and you can hear it: a faint crackle coming off the cables. Those cables are surprisingly slim, no thicker than a wrist, and between them they are moving enough energy to run a city. The reason they can do it without glowing red hot is that the potential difference across them has been pushed up to hundreds of thousands of volts before the energy was let anywhere near them, and raising the voltage is the same thing as shrinking the current.

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Tathmini ya Somo

Hongera kwa kukamilisha somo la Electricity Transmission And Distribution. Sasa kwa kuwa umechunguza dhana na mawazo muhimu, ni wakati wa kuweka ujuzi wako kwa mtihani. Sehemu hii inatoa mazoezi mbalimbali maswali yaliyoundwa ili kuimarisha uelewaji wako na kukusaidia kupima ufahamu wako wa nyenzo.

Utakutana na mchanganyiko wa aina mbalimbali za maswali, ikiwemo maswali ya kuchagua jibu sahihi, maswali ya majibu mafupi, na maswali ya insha. Kila swali limebuniwa kwa umakini ili kupima vipengele tofauti vya maarifa yako na ujuzi wa kufikiri kwa makini.

Tumia sehemu hii ya tathmini kama fursa ya kuimarisha uelewa wako wa mada na kubaini maeneo yoyote ambapo unaweza kuhitaji kusoma zaidi. Usikatishwe tamaa na changamoto zozote utakazokutana nazo; badala yake, zitazame kama fursa za kukua na kuboresha.

  1. Which transformer is placed between a power station and the transmission cables, and what is the effect on the current in those cables? A. A step-up transformer, which increases the current B. A step-up transformer, which decreases the current C. A step-down transformer, which increases the current D. A step-down transformer, which decreases the current Answer: B
  2. A fixed amount of electrical power is transmitted along an unchanged line. The transmission voltage is doubled. What happens to the power wasted heating the cables? A. It doubles B. It halves C. It falls to one quarter D. It is unchanged Answer: C
  3. A transmission line carries a current of 50 A and its cables have a total resistance of 4.0 ohms. What is the power wasted heating the cables? A. 200 W B. 2.0 kW C. 10 kW D. 200 kW Answer: C
  4. Why is the voltage reduced by a transformer before the supply reaches houses in a street? A. To increase the amount of energy delivered each second B. To produce a voltage that is safe for local consumers C. To reduce the resistance of the transmission cables D. To change the alternating supply into a direct one Answer: B
  5. Which list gives the essential parts of a transmission and distribution system in the order that energy passes through them? A. Power station, step-down transformer, transmission cables, step-up transformer, consumers B. Power station, step-up transformer, transmission cables, step-down transformer, consumers C. Power station, transmission cables, step-up transformer, step-down transformer, consumers D. Step-up transformer, power station, transmission cables, consumers, step-down transformer Answer: B

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