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HSC Physics Question Thread

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mrsc:
Hey just wondering the logic behind this question. The answer was B, but I somehow don't seem to get why. Is it because decreasing the number of secondary coils reduces the emf in them which causes an increased deflection due to the change in magnetic flux?

fun_jirachi:
Hey there!

The galvanometer detects changes in current - so when we look at the transformer equation \(\frac{V_P}{V_S} = \frac{I_S}{I_P} = \frac{N_P}{N_S}\), we can deduce that to increase the deflection in the galvanometer ie. increasing \(I_S\), we can do a few things: increase the number of primary coils, decrease the number of secondary coils, increase the primary voltage, etc. We also can rule out C and D because the primary function of a resistor is to reduce current (not what we want here!) and copper cores perform worse as compared to iron cores. Hence, the answer is B.

Hope this helps :)

Coolmate:
Hey Physics Gang! ;)

Could someone please explain to me why the answer is 'C'? Does it involve deriving another formula, or the like out of this formula: \[dsin\theta = m\lambda\]
Thanks in advance!
Coolmate 8)

1729:

--- Quote from: Coolmate on August 11, 2020, 07:44:31 pm ---Hey Physics Gang! ;)

Could someone please explain to me why the answer is 'C'? Does it involve deriving another formula, or the like out of this formula: \[dsin\theta = m\lambda\]

Thanks in advance!
Coolmate 8)

--- End quote ---
The answer is C  because it's a dark spot, it means they're out of phase, so p2 would have to be longer than p1 by a factor of (2n(lambda)+1)/2 to create perfectly destructive interference. As you can see by the center bright spot, that's what happens when p1 and p2 are the same length. This means that the 2 dark spots closest to the center will be half a wavelength out of phase which is the closest difference that creates a dark spot. This means that it would be lambda/2, and since the dark spot we want is one dark spot further, the difference would have to be 3(lambda)/2

Coolmate:

--- Quote from: 1729 on August 11, 2020, 08:01:50 pm ---The answer is C  because it's a dark spot, it means they're out of phase, so p2 would have to be longer than p1 by a factor of (2n(lambda)+1)/2 to create perfectly destructive interference. As you can see by the center bright spot, that's what happens when p1 and p2 are the same length. This means that the 2 dark spots closest to the center will be half a wavelength out of phase which is the closest difference that creates a dark spot. This means that it would be lambda/2, and since the dark spot we want is one dark spot further, the difference would have to be 3(lambda)/2

--- End quote ---

Thanks 1729!
This makes much more sense now :)

Coolmate 8)

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