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Wonders of Physics

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2016 Pure Physics P1 Q40 – Voltage and Power of Bulb Y when X is switched off

2016 PPp1q40

Solutions: Option C
[There is another similar question in 2013 Nov Pure Physics P1Q40. The answer is Option C too. Refer to the last section of this post]

Refer to the 2 videos below. The 1st one is faster if you know that the bigger the resistance, by proportion, the bigger the potential difference of the component as it will take a larger portion of the emf wrt to the other components in series. This method is especially useful for MCQ.

If you are still unsure, you may put in values to find the I, V and P across the components. This will be more tedious and time-consuming.

Another similar question is 2013 Nov Pure Physics P1 Q40.

2013 PP p1q40

Solutions: Option C


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Induced emf not affected by resistance of wire

The electromotive force (e.m.f.) induced in a conductor moving at right-angles to a magnetic field does not depend upon

A) the length of the conductor.
B) the resistance of the conductor.
C) the speed of the conductor.
D) the strength of the magnetic field.

Solutions: B

The longer the wire, the rate in which the magnetic lines of force cutting the wire is greater. So A is true.

As it is a wire and not a closed circuit, no induced current is formed. Hence induced emf is produced and the resistance of the wire will not affect the in emf induced.