Physics (9-1) - 0972 CIE

Electric Circuits

Overzicht

Flip one switch and a whole room of lights comes on, yet unplug one fairy light and the rest stay glowing. The difference is whether the components are wired in series, one after another, or in parallel, side by side. How you connect components decides the current through each, the voltage across each, and the total resistance of the circuit.

In this lesson you will read and draw circuit diagrams, use the rule that current is the same everywhere in a series circuit, add e.m.f.s and resistances in series, use the junction rule for currents in parallel, find the combined resistance of resistors in parallel, and explain why lights at home are wired in parallel. Every calculation shows the equation, the substitution and the answer with units.

Doelstellingen

  1. Draw and interpret circuit diagrams containing cells, batteries, power supplies, generators, potential dividers, switches, resistors (fixed and variable), heaters, thermistors (NTC only), light- dependent resistors (LDRs), lamps, motors, bells, ammeters, voltmeters, magnetising coils, transformers, fuses and relays and know how these components behave in the circuit
  2. Know that the current at every point in a series circuit is the same
  3. Know how to construct and use series and parallel circuits
  4. Calculate the combined e.m.f. of several sources in series
  5. Calculate the combined resistance of two or more resistors in series
  6. State that, for a parallel circuit, the current from the source is larger than the current in each branch
  7. State that the combined resistance of two resistors in parallel is less than that of either resistor by itself
  8. State the advantages of connecting lamps in parallel in a lighting circuit
  9. [Supplement] Draw and interpret circuit diagrams containing diodes and light-emitting diodes (LEDs) and know how these components behave in the circuit
  10. [Supplement] Recall and use in calculations, the fact that: (a) t he sum of the currents entering a junction in a parallel circuit is equal to the sum of the currents that leave the junction (b) t he total p.d. across the components in a series circuit is equal to the sum of the individual p.d.s across each component (c) t he p.d. across an arrangement of parallel resistances is the same as the p.d. across one branch in the arrangement of the parallel resistances
  11. [Supplement] Explain that the sum of the currents into a junction is the same as the sum of the currents out of the junction
  12. [Supplement] Calculate the combined resistance of two resistors in parallel

Lesnotitie

Every wired device, from a torch to a house, is a network of series and parallel connections, and engineers design them by working out currents, voltages and resistances. This topic is a steady source of exam marks because the rules are clear and the calculations follow a few short equations applied carefully.

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Lesevaluatie

Gefeliciteerd met het voltooien van de les op Electric Circuits. Nu je de sleutelconcepten en ideeën, het is tijd om uw kennis op de proef te stellen. Deze sectie biedt een verscheidenheid aan oefeningen vragen die bedoeld zijn om uw begrip te vergroten en u te helpen uw begrip van de stof te peilen.

Je zult een mix van vraagtypen tegenkomen, waaronder meerkeuzevragen, korte antwoordvragen en essayvragen. Elke vraag is zorgvuldig samengesteld om verschillende aspecten van je kennis en kritisch denkvermogen te beoordelen.

Gebruik dit evaluatiegedeelte als een kans om je begrip van het onderwerp te versterken en om gebieden te identificeren waar je mogelijk extra studie nodig hebt. Laat je niet ontmoedigen door eventuele uitdagingen die je tegenkomt; beschouw ze in plaats daarvan als kansen voor groei en verbetering.

  1. In a series circuit, the current is A. largest near the battery B. the same at every point C. used up by each component D. different in each component Answer: B
  2. Two 1.5 V cells are connected in series the same way round. The combined e.m.f. is A. 0.75 V B. 1.5 V C. 3.0 V D. 4.5 V Answer: C
  3. Resistors of 3 ohm and 6 ohm in series have a combined resistance of A. 2 ohm B. 4.5 ohm C. 9 ohm D. 18 ohm Answer: C
  4. Resistors of 4 ohm and 12 ohm in parallel have a combined resistance of A. 3 ohm B. 8 ohm C. 16 ohm D. 48 ohm Answer: A
  5. Lamps in a house are wired in parallel mainly so that A. they share the current B. each can be switched independently and shines at full brightness C. they use less energy D. one failing switches them all off Answer: B

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