Opted test, Physics #35

[NatashaColorado]

can anyone explain Physics #35 question, where a 12-V battery has an internal resistance of 1 Ohm. "What is the current in the circuit?" The answer is 3 Amp.
I would like to use V(terminal) = Emf (battery) - IxR, but since there is no terminal voltage mentioned in the problem, how do I calculate it?

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[EyEnStein 07]

took the algebra physics II a really long time ago..and i take physics II calc based next semester....so maybe what i can tell you might help you out.

I also remmeber some formula like E = IR + Ir
im not sure how much that may help, but im sure you can use that along with the formula i listed. I tried a few things but couldnt get what "the answer" is...i kept getting 6.

Do post the solution if you figure it out.

 

[blysssful]

opted sample test errors/typos
test download: https://www.ada.org/oat/oat_sample_test.pdf

I have compiled a list of errors on the OPTED sample test (found at the link above). Please let me know if have found any additional typos.

The key goes like this:

• Opted Faulty Answer
  
  
• Most Correct Answer

NATURAL SCIENCES

44. If the mass percent of oxygen in a nitrogenoxygen
compound is known, given the mass
percent of oxygen, all of the following are
needed to determine the molecular formula of
a nitrogen-oxygen compound EXCEPT one.
Which one is this EXCEPTION?
A. Atomic mass of nitrogen
B. Atomic mass of oxygen
C. Avogadro's number
D. Empirical formula
E. Molar mass of the compound

**Although the Empirical formula is NOT needed, neither is Avogadro's number. There is no logical reason why you would need Avogadro's number.
-> The empirical formula would be useful for calculating the molecular formula, HOWEVER you can just as well use the 'mass percent of oxygen' combined with the atomic masses of each to figure out the molecular formula.
-> You would not use Avogadro's number to calculate the molecular formula.



61. A 0.60 M solution is made by dissolving solid
compound X in water. After ten seconds, the
concentration of X is 0.40 M. All of the
following could account for these results
EXCEPT one. Which one is this
EXCEPTION?
A. Precipitation
B. Neutralization
C. Evaporation
D. Decomposition
E. Disproportionation

**The answer given, Precipitation, would actually result in the decrease of the concentration.
--> On the other hand, Evaporation results in a decrease in volume. Molarity is found by using the formula: M = mols/volume -- thus, a decrease in volume would INCREASE the concentration, making this the correct answer.



93. What is the hybridization of a nitrogen atom if
it forms two σ two π bonds?
A. sp
B. sp2
C. sp3
D. sp3d2

** sp3 hybridization results from sigma bonds, and does not contain pi bonds.--> sp hybridization is a result of 2 sigma and 2 pi bonds --> making A the right answer.

PHYSICS

35. A 12-volt battery with an internal resistance of
1-Ω resistor. Which of the following is the
current in amperes that flows in the circuit.
A. 4
B. 3
C. 9
D. 12
E. 48

** 3 doesn't even make sense as an answer.
--> The current is found by using the formula: i = V/R. Plug in 12 as the voltage (V) and 1 as the resistance (R) --> i = 12/1 = 12.




(NOTE: I HAVE NOT CONFIRMED THIS LAST PROBLEM (PHYSICS # 39, please let me know if you disagree!)

39. What is the focal length in cm of a lens that
produces an image 30 cm behind it when the
object is placed 6 cm in front of it?
A. 7.5
B. 36
C. 5.0
D. 24
E. 18.0
**The focal length is found by: 1/f = 1/o + 1/i. Since the image is behind the lens, i will have a negative value (i = -30). Since the object is place in front of the lens, o will have a positive value (o = 7.5). SO, 1/f = 1/-30 + 1/6. Solve for f, and you get 7.5.



There you have it! I have confirmed the other answers with professors at my university (except physics #39) . If you disagree w/ anything, please indicate the number and why.

This might help.

Oh, and Voltage = 12V in problem 35. That's pretty straightforward.

 

[EyEnStein 07]

Oh wow. that really was simple...
i thought internal resistance was calculated differently. I guess it
didnt matter here since no other information was given.

 

[blysssful]

Oh wow. that really was simple...
i thought internal resistance was calculated differently. I guess it
didnt matter here since no other information was given.

I think it was one of those "it CAN'T be that simple" problems

 

[NatashaColorado]

This might help.

Oh, and Voltage = 12V in problem 35. That's pretty straightforward.

I ABSOLUTELY agree with you on question 93 - it was driving me crazy as I could not see sp3 with 2 pi orbitals. I thought , perhaps, NH2- , where there is 2 sigma bonds and 2 lone pairs? But lone pairs are not pi orbitals - they are hybridized, so, the answer has to be sp.

Physics q.#39 is correct - it's 5cm. The image behind the LENSE is possitive, which is different from the image behind the mirror (negative). Object is always positive - it can only be negative in the two lense system. So, the formula will be 1/30 + 1/6 = 1/f, which gives you f= 5cm. The trick is to remember that mirrors and lenses have reverse +/- for image distance and object is always positive.

Physics #35. I am with you on that. I spoke with my professor and he said: "We can estimate the maximum current that the battery can supply by setting its terminal voltage to 0. Then, Imax = V/R = 12A. Since no other information is provided, it should be the right answer"

What about q.# 86: How many pi orbitals does pyridine possess? The answer is 7, and from what I understand this is an aromatic ring and it has 6 pi electrons. The lone pair of Nitrogen atom is not part of the pi system - it's in the plane of the ring. Somehow they counted it into the answer and I don't know why.

 

[jc10101]

I ABSOLUTELY agree with you on question 93 - it was driving me crazy as I could not see sp3 with 2 pi orbitals. I thought , perhaps, NH2- , where there is 2 sigma bonds and 2 lone pairs? But lone pairs are not pi orbitals - they are hybridized, so, the answer has to be sp.

Physics q.#39 is correct - it's 5cm. The image behind the LENSE is possitive, which is different from the image behind the mirror (negative). Object is always positive - it can only be negative in the two lense system. So, the formula will be 1/30 + 1/6 = 1/f, which gives you f= 5cm. The trick is to remember that mirrors and lenses have reverse +/- for image distance and object is always positive.

Physics #35. I am with you on that. I spoke with my professor and he said: "We can estimate the maximum current that the battery can supply by setting its terminal voltage to 0. Then, Imax = V/R = 12A. Since no other information is provided, it should be the right answer"

What about q.# 86: How many pi orbitals does pyridine possess? The answer is 7, and from what I understand this is an aromatic ring and it has 6 pi electrons. The lone pair of Nitrogen atom is not part of the pi system - it's in the plane of the ring. Somehow they counted it into the answer and I don't know why.

i agree with yout ochem #86, i didnt get that at all.

 

[KHE]

can anyone explain Physics #35 question, where a 12-V battery has an internal resistance of 1 Ohm. "What is the current in the circuit?" The answer is 3 Amp.
I would like to use V(terminal) = Emf (battery) - IxR, but since there is no terminal voltage mentioned in the problem, how do I calculate it?

The answer is C or the longest answer.

 

[brooke0814]

i agree with yout ochem #86, i didnt get that at all.

#86 I thought since they are asking how many orbitals, that because there are 6 pi electrons in the system, that the answer is 3 orbitals. Anyone else with me?

On #84, shouldn't the 12 hydrogens produce quartets, not doublets? I see where the septets are, but the other carbons are adjacent to carbons with 3 total hydrogens...making quartets on the spectrum. Correct?

 

[ILOD]

Bump this. for solosauoptom

 

[soloSAUoptom]

Bump this. for solosauoptom

Thanks

 

[lsmc888]

oh thank god i read this
i took the practice and got these wrong and was like, this has to be a mistake.