Fig. 6.1 shows the circuit diagram for a flashlight (torch). The electromotive force (e.m.f.) of the battery is $$$4.5 \mathrm{~V}$$$. The circuit contains a $$$60 \Omega$$$ fixed resistor. The current in the light-emitting diode (LED) is 0.020A. Explain why the LED does not light up if the battery is reversed.

Physics

IGCSE&ALevel

CAIE

Exam No：0625_w23_qp_42 Year：2023 Question No：6(b)

Answer:

Knowledge points:

4.3.1.1 Draw and interpret circuit diagrams containing sources, switches, resistors (fixed and variable), heaters, thermistors, light-dependent resistors, lamps, ammeters, voltmeters, galvanometers, magnetising coils, transformers, bells, fuses and relays

4.3.1.2 Draw and interpret circuit diagrams containing diodes

4.3.2.1 Understand that the current at every point in a series circuit is the same

4.3.2.2 Give the combined resistance of two or more resistors in series

4.3.2.3 State that, for a parallel circuit, the current from the source is larger than the current in each branch

4.3.2.4 State that the combined resistance of two resistors in parallel is less than that of either resistor by itself

4.3.2.5 State the advantages of connecting lamps in parallel in a lighting circuit

4.3.2.6 Calculate the combined e.m.f. of several sources in series

4.3.2.7 Recall and use the fact that the sum of the p.d.s across the components in a series circuit is equal to the total p.d. across the supply

4.3.2.8 Recall and use the fact that the current from the source is the sum of the currents in the separate branches of a parallel circuit

4.3.2.9 Calculate the effective resistance of two resistors in parallel

4.3.3.1 Describe the action of a variable potential divider (potentiometer)

4.3.3.2 Describe the action of thermistors and light- dependent resistors and show understanding of their use as input transducers

4.3.3.3 Describe the action of a relay and show understanding of its use in switching circuits

4.3.3.4 Describe the action of a diode and show understanding of its use as a rectifier

4.3.3.5 Recognise and show understanding of circuits operating as light-sensitive switches and temperature-operated alarms (to include the use of a relay)

Answer:

Knowledge points:

Solution:

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