MC Question... (1 Viewer)

[Blitz_N7]

What is the explanation for this question given that the answer is A?

 

[ThreeSciences]

To increase the deflection on the galvanometer, you must increase the current in the secondary coil. This is a step up transformer:

Less -> more coils = voltage increases (power remains constant, so current must decrease in order to maintain the law of conservation of energy). Conversely, more coils -> less coils = voltage decreases (hence current increases).

Since the number of turns in the primary coil is decreasing, that makes the secondary coil have a larger ratio of turns compared to the primary coil than before, thus stepping up the voltage and decreasing the current, so as far as I can tell, the answer actually should be B - decrease the number of turns in the secondary coil.

If this question is from a Brian Shadwick book don't look too surprised, but someone correct me if I'm wrong...

 

[anomalousdecay]

Answer is actually B.



To increase secondary coil current, you need to either decrease secondary turns, increase primary turns or both. Or you could also increase the magnitude of the voltage source at the primary.

 

[Blitz_N7]

That's my thought process as well. Btw it was Q18 from 2015 HSC exam.

 

[anomalousdecay]

Yeah BOSTES also says answer is A.

Idk who thought a galvanometer's readings are based off the voltage. It's supposed to be based off the current.

I'd still say that B is the correct answer.

Your teacher probably said more than that.

 

[InteGrand]

The HSC has been known to have physically incorrect answers as their stated correct answers in the past for HSC Physics.

 

[leehuan]

Sudden realisation that I got ripped off a mark in the HSC. But it's beyond late to complain about that now.