# Multiple Choice (1 Viewer)

#### anomalousdecay

The answer is what Fizzy said
Does it have something to do with back emf?

#### Menomaths

##### Exaı̸̸̸̸̸̸̸̸lted Member
Does it have something t do with back emf?
I don't know...I can't remember. Like I said earlier I'm tired af atm

#### uart

##### Member
The answer is what Fizzy said
Only if the motor is supplied from a constant voltage supply rather than a constant current. Something that the question did NOT specify!

#### anomalousdecay

Too tired to check.

Game-over HSC. Well played Physics manipulative questions that are too hard to get all right in 35 minutes.
Well played.

19/20 in chem in 20 mins. is good enough for me.

#### Menomaths

##### Exaı̸̸̸̸̸̸̸̸lted Member
Only if the motor is supplied from a constant voltage supply rather than a constant current. Something that the question did NOT specify!
Hmm you seem to be in the know. I hope you're correct haha cause I put b.

#### anomalousdecay

Hmm you seem to be in the know. I hope you're correct haha cause I put b.
Same.

#### uart

##### Member
Hmm you seem to be in the know. I hope you're correct haha cause I put b.
Maybe they'll realize that they stuffed up (ambiguous question) and mark both b and d as correct.

If they were just testing that students knew that a radial field implies that torque doesn't vary with angular position, then they might have expected a constant current assumption and hence answer "b'.

On the other hand they may have been trying to test if students understood that back EMF increases with motor speed, and hence expected the assumption of constant voltage and answer "d". If this was the case however they *really* should have specified constant voltage operation.

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#### Menomaths

##### Exaı̸̸̸̸̸̸̸̸lted Member
Maybe they'll realize that they stuffed up (ambiguous question) and mark both b and d as correct.

If they were just testing that students knew that a radial field implies that torque doesn't vary with angular position then they might have expected a constant current assumption and hence "b'.

One the other hand they may have been trying to test if students understood that back EMF increases with motor speed, and hence expected the assumption of constant voltage and answer "d". If this was the case however they *really* should have specified constant voltage operation.
Hmm.. This issue has to be raised.

#### anomalousdecay

Maybe they'll realize that they stuffed up (ambiguous question) and mark both b and d as correct.

If they were just testing that students knew that a radial field implies that torque doesn't vary with angular position, then they might have expected a constant current assumption and hence answer "b'.

One the other hand they may have been trying to test if students understood that back EMF increases with motor speed, and hence expected the assumption of constant voltage and answer "d". If this was the case however they *really* should have specified constant voltage operation.

It says DIRECT CURRENT, so I think we are stuffed.

#### uart

##### Member
It says DIRECT CURRENT, so I think we are stuffed.
It says DC motor. DC simply means unidirectional current (or voltage), it makes no implication of whether either the voltage or current is constant.

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#### anomalousdecay

Yeah. Matter needs to be raised.

#### Menomaths

##### Exaı̸̸̸̸̸̸̸̸lted Member
uart, can you somehow raise the issue for us? (i'm too lazy)

#### Randox

##### Member
Protest to BOS I say

How often are two answers awarded? I put b...

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#### RealiseNothing

##### what is that?It is Cowpea
Protest to BOS I say

How often are two answers awarded? I put b...
It has happened in the past, but it is very rare.

#### hjed

##### Member
Q12, (a) is most correct. Meissner effect doesn't have anything to do with crystal lattice structure or the balancing of any gravitational forces anyway i believe.

14 should be (b) small values of d create very large values of E, and large values of d create very small values of E (suggested by your explanation too)

15 is (a) (panda15 explained already)

+Q17 looks like about 4 wrong
for Q12, the Meissner effect is caused due to BCS which is due to the crystal lattice structure, the Messiner effect excludes magnetic fields. However, for long answer versions of this question you usually have to say the forces balance to allow the magnet to levitate. (which is what the question is asking)

#### panda15

##### Alligator Navigator
for Q12, the Meissner effect is caused due to BCS which is due to the crystal lattice structure, the Messiner effect excludes magnetic fields. However, for long answer versions of this question you usually have to say the forces balance to allow the magnet to levitate. (which is what the question is asking)
I'm pretty sure that the question just wants the textbook answer, which would be a).

#### Fizzy_Cyst

##### Well-Known Member
We only look at motors which have a constant supply voltage, so whilst I wholeheartedly agree with both answers being correct (in REAL life), unfortunately, I would say that only D would be correct (in HSC life)

#### anomalousdecay

We only look at motors which have a constant supply voltage, so whilst I wholeheartedly agree with both answers being correct (in REAL life), unfortunately, I would say that only D would be correct (in HSC life)

The same thing will probably happen with the photocell question too.
So much debate. We have to see what happens later on.

#### Hypem

##### Member
Got 17/20, 18/20 if 17B ends up being accepted lol

#### j1mmy_

##### Member
Protest to BOS I say

How often are two answers awarded? I put b...
2011 Biology Paper.