VCE Physics Question Thread!

[VinnyD]

what does the study design point mean "compare alternating voltage expressed as the root-mean-square (rms) to a constant DC voltage developing
the same power in a resistive component"? i cant find much information regarding this point in the book, can anyone help?

I'm pretty sure its just using the root mean square value (root 2 formula) to just convert AC into a constant output. Kind of making AC into DC. (ac has peaks higher than rms value, so the rms value gives us the average value for the ac current that's lower than the peak.) Hope this helps

[Yertle the Turtle]

what does the study design point mean "compare alternating voltage expressed as the root-mean-square (rms) to a constant DC voltage developing
the same power in a resistive component"? i cant find much information regarding this point in the book, can anyone help?

Just to add to what VinnyD said, the RMS voltage is the DC equivalent of the AC voltage, being the average value of the sine curve. If you think about the average value of a sine wave it is at pi/4 radians, which is 1/sqrt(2), so to find RMS voltage from peak to peak voltage you multiply by 1/sqrt(2). Hope this helps.

[Ghost_]

Hey,

In VCAA's answers for the 2017 VCE Physics exam (Q9c), they showed a graph that looked like a connect the dots instead of a smooth parabolic curve. Why didn't they sketch a smooth curve of best fit instead of just connecting the dots?
-Thanks

[minhalgill]

do we take the value of g to be 9.8 or 10??? and how many significant figuires should our answers be to?

[S200]

Always 9.8

Ans also always 3 sig fig, plus scientific notation if needed.

[Yertle the Turtle]

do we take the value of g to be 9.8 or 10??? and how many significant figures should our answers be to?

As S200 has said, g is always 9.8. However, for the s.f question, you always use the part of the question with the fewest significant figures as your base. If the part of the question with the least precision has 3 s.f. then your answer should be to 3 s.f. You just always use the minimum level of accuracy that the question uses.

[S200]

However, for the s.f question, you always use the part of the question with the fewest significant figures as your base. If the part of the question with the least precision has 3 s.f. then your answer should be to 3 s.f. You just always use the minimum level of accuracy that the question uses.

What do you do when the question has min 4 sig fig?
Do you go four, or three?

[Yertle the Turtle]

What do you do when the question has min 4 sig fig?
Do you go four, or three?

In that case you would go 4 sig figs. You always have to follow the question in what answers you give.

[S200]

In that case you would go 4 sig figs. You always have to follow the question in what answers you give.

Hmmm...
Dat means all my answers are wrong then...
I always go to 2 sig figs after the decimal (so three overall), and only at the very very end of all the working out...

Like, if I have \(12.3476 \times 15.9347\), which equals \(196.755302\), I would answer that as \(196.76\)

For larger numbers, like \(10456.789 \times 164.9876\), which equals \(1725240.52082\), I would answer \(1.73\times 10^6\).
How would you answer those two?

[Bri MT]

Hmmm...
Dat means all my answers are wrong then...
I always go to 2 sig figs after the decimal (so three overall), and only at the very very end of all the working out...

Like, if I have \(12.3476 \times 15.9347\), which equals \(196.755302\), I would answer that as \(196.76\)

For larger numbers, like \(10456.789 \times 164.9876\), which equals \(1725240.52082\), I would answer \(1.73\times 10^6\).
How would you answer those two?

I would answer as 196.755 and 1.725241 * 10^6 respectively.

Especially if this was a data analysis type question, I would not consider 3 sig figs as a standard "rule"

[S200]

I would answer as 196.755 and 1.725241 * 10^6 respectively.

Especially if this was a data analysis type question, I would not consider 3 sig figs as a standard "rule"

Yeah ok.
But doing 1.725241 * 10^6 seems to kinda defeat the purpose of scientific notation. You may as well just write it out in full.

[sweetiepi]

Yeah ok.
But doing 1.725241 * 10^6 seems to kinda defeat the purpose of scientific notation. You may as well just write it out in full.

Scientific notation will always be the preferred format for something like that, I got stung a quite a few times for not writing out big/small numbers in scientific notation, even though it feels counter-intuitive (I did that recently on a lab report and lost marks I shouldn't have otherwise. #salty)

I would also not use the 3-sig figs rule as a rule, answers should typically depend on the sig figs on the values given in the question stem.

[Ghost_]

Are we supposed to know how to answer past paper questions from the topic: Electronics and photonics because I remember covering it last year but this year we barely studied that specific area, at least to the extent asked in problems involving things such as: voltage divider, lux, leds in circuits and sketching circuits with all sorts of symbols etc.
-Thanks

[KiNSKi01]

YOO. What am I missing here? :/

A steel bar is moved at a constant speed of v m/s perpendicular to magnetic field (directed into page). The steel bar is 0.8 m long. The magnetic field strength is 8 x 10^-3 T.

If the emf between the ends of the steel bar is 30 mV what is the constant speed?

I'm not sure how I can use the extra info regarding voltage to help calculate answer

[VinnyD]

YOO. What am I missing here? :/

A steel bar is moved at a constant speed of v m/s perpendicular to magnetic field (directed into page). The steel bar is 0.8 m long. The magnetic field strength is 8 x 10^-3 T.

If the emf between the ends of the steel bar is 30 mV what is the constant speed?

I'm not sure how I can use the extra info regarding voltage to help calculate answer

In this case i think its the special formula for the emf (E=LVB) where L= length, v=velocity and B= mag field. Very specific question though. Just rearrange for V as we are given everything else. Let me know if it's something different