TrueTears question thread

[TrueTears]

Well I'm an idiot for not knowing that was the actual angle...you learn something new everyday!

Yeah that's confusing lol I hate not knowing why things are the way they are, but I guess that's just part of the limitations of VCE physics.

Yeah haha, I guess I'll just ignore it lol.

Thanks for your help again!

[dejan91]

Np

[TrueTears]

Just a quick question, the brushes in a DC motor basically just allows charge to flow from the power supply to the coil via the commutator and it also allows the commutator to turn more smoothly.

Is that right?

[Mao]

Just a quick question, the brushes in a DC motor basically just allows charge to flow from the power supply to the coil via the commutator and it also allows the commutator to turn more smoothly.

Is that right?

The brushes ensure the commutator stays electrically connected to the power supply.

[TrueTears]

Just a quick question, the brushes in a DC motor basically just allows charge to flow from the power supply to the coil via the commutator and it also allows the commutator to turn more smoothly.

Is that right?

The brushes ensure the commutator stays electrically connected to the power supply.

Thanks again Mao XD

[homghomg1]

Another question:

(Image removed from quote.)

First two are: NO CHANGE, DECREASE respectively.

What's the third one? Rather how do you work it out?

 I was quite confused when i first did that question and thought they were wrong, but the reason is that for a split second, when the commutator is reversing the direction of current in the coil, and the ends of the coil are not touching the metal part, there is zero current.

It's a pretty good question, they should've given a better explanation though, pretty useless if they just state the answer. Specially since these exams don't hesitate to put all sorts of wrong answers which contradict with answers from other papers.

[TrueTears]

Another question:

(Image removed from quote.)

First two are: NO CHANGE, DECREASE respectively.

What's the third one? Rather how do you work it out?

 I was quite confused when i first did that question and thought they were wrong, but the reason is that for a split second, when the commutator is reversing the direction of current in the coil, and the ends of the coil are not touching the metal part, there is zero current.

It's a pretty good question, they should've given a better explanation though, pretty useless if they just state the answer. Specially since these exams don't hesitate to put all sorts of wrong answers which contradict with answers from other papers.

lol that is so sly. But still it's quite flawed... how do you know what the cummutator is touching when it's at it's horizontal position, it could be touching the brushes and then when it reaches the vertical position, it'd be off the brushes for a split second which means it should be decreased. Anyhow, weird question.

Thanks for your help!

[ngRISING]

how many questions do i need to get right for a grade C.

[TrueTears]

Also another quick question, standing wave formulas are the same for strings tied at both ends and a pipe open at both ends right?

[kurrymuncher]

Also another quick question, standing wave formulas are the same for strings tied at both ends and a pipe open at both ends right?

Yes

[TrueTears]

Also another quick question, standing wave formulas are the same for strings tied at both ends and a pipe open at both ends right?

Yes

Thanks

[appianway]

Just remember that the wavelength in air for a wave produced in a string will be different to the wavelength produced in the string, unless the velocity of the wave in the string is the same as the speed of sound.

[TrueTears]

Just remember that the wavelength in air for a wave produced in a string will be different to the wavelength produced in the string, unless the velocity of the wave in the string is the same as the speed of sound.

Yeap, thanks for that

[TrueTears]

Also another question: (can someone just check my reasoning)



Answer is D.

My reasoning: As the magnet falls through the loop, the magnetic is pointing upwards (north to south). So the flux is increasing upwards as it falls, thus to oppose this the loop sets up a magnetic field downwards, using RHG rule, the current is clockwise.

As the magnet falls through, the magnetic field is going upwards (out from north and into south). So the flux is decreasing upwards as it falls out, so the loop sets up a magnetic field upwards to compensate for this loss. Thus the current goes anticlockwise.

Is my reasoning right?

The reason I'm just confirming is because I do it the vector way but I thought it'd be good if I can understand this method as well.

Thanks!

[appianway]

Did you get the correct answer? I would've said that the initially the magnetic field was increasing DOWNWARDS, as the magnetic field is drawn for N into S. The initial induced current must thus produce an upwards flux, and is therefore anticlockwise.

But you never know. I could be wrong... I'm doing other homework at the moment, so maybe I misread the diagram or did something careless