Section I - Multiple Choice (2 Viewers)

[nucgaek]

10 wasn't the peak, ~8 was. If you use 8*10^-6 you get B.

Using a ruler... pretty much got the exact answer for the peak as B, so i just went for it

EDIT: Also, someth1ng, I've definitely learnt the induction cooktop pans are specially designed to have greater resistivity than tranditional pans, as traditional pans want to have as close to 0 resistivity as possible.

 

[deswa4]

I'm quite sure if you pick high resistance, smaller currents are also induced and hence less heat but I'm not sure. It might well be 19D.

12 is A because you need to choose one that is sensitive to all thermal radiation emitted.

I think you mean 20, but the answer is definitely B.

If you calculate the wavelength of EMR required to produce 0.03eV of energy, you end up finding it to be 41µm, which is way off the scale of the Typical Human BBR Curve. To generate 0.17eV on the other hand, you need a wavelength of 11µm which is most certainly on the graph.

Hence the answer is B.

 

[cartoonmaiz]

This feeling is horrible... im looking at 2-3 mc questions wrong...

 

[someth1ng]

I still think it is quite debatable but it won't be as sensitive as option A. Option B will detect up to roughly the peak but you need to be able to detect ALL of it to be able to detect most of the heat...

 

[oh well]

I still think it is quite debatable but it won't be as sensitive as option A. Option B will detect up to roughly the peak but you need to be able to detect ALL of it to be able to detect most of the heat...

Yeah that's exactly what I said in one of my posts, 20 is defs A !

 

[cartoonmaiz]

Hey some1thing how did you go for the rest of the test?

 

[someth1ng]

Hey some1thing how did you go for the rest of the test?

I did good except I'm not (never am) confident with Astrophysics.

 

[OlliePOP95]

P-type has less electrons than Silicon, and Gallium has more electrons, therefore would make an n-type semiconductor....?

 

[chriss95]

19 is C. Because remember a strategy for lessening the heating produced by eddy currents in transformers you use ferrite instead of iron; because ferrite has higher resistance

 

[mickstarify]

Gallium is group 3, and therefore has 3 electrons as apposed to silicon's 4. so there is a deficit of electrons, meaning p-type

 

[microsh]

hate to tell this but 20 isnt B its A, coz when u calculate the energy of the 10um wavelength you get 0.13, thats lower than B which is 0.17
so the human body wavelength which is around 0.13 would not have enough energy to create a photoelectric thing in B, making the detector useless
i hope i am wrong coz i chose B

 

[mickstarify]

hate to tell this but 20 isnt B its A, coz when u calculate the energy of the 10um wavelength you get 0.13, thats lower than B which is 0.17
so the human body wavelength which is around 0.13 would not have enough energy to create a photoelectric thing in B, making the detector useless
i hope i am wrong coz i chose B

oh well, 1 mark

 

[deswa1]

Here is my MC answers:
1. D
2. A
3. C
4. B
5. C
6. C
7. B
8. A
9. B
10. D
11. C
12. A
13. B
14. D
15. D
16. C
17. B
18. C
19. D
20. A

Q19: I actually believe that it should be C - low electrical resistance.
Q20: To said to detect thermal radiation, this means that you use the wavelength that will allow the most radiation to be detected. Using one that is a peak means that less light is detected and hence, less sensitive and hence, less suitable.

I think all your answers are right, except 20 (B). 19 is indeed D because a high AC voltage means greater change in flux (more eddy currents), and high electrical resistance in the pot base means greater heat developed (as P= I^2R).

Surprisingly my 'alt' said exactly what I wanted to say haha. Yeah I got all of your answers someth1ng except I put B for 20. I reasoned that near the peak of the curve is where most of the energy is emitted and this corresponds to around 0.17 or B. I might be wrong though

 

[Dedopcat]

This feeling is horrible... im looking at 2-3 mc questions wrong...

get over it man, people I know including me are looking at 15/20 best case scenario so

 

[someth1ng]

Surprisingly my 'alt' said exactly what I wanted to say haha. Yeah I got all of your answers someth1ng except I put B for 20. I reasoned that near the peak of the curve is where most of the energy is emitted and this corresponds to around 0.17 or B. I might be wrong though

Yeah, it depends on what they mean by "most suitable". I wonder if Fizzy_Cyst would know the answer to it...

 

[brianphamm]

19 is C. Because remember a strategy for lessening the heating produced by eddy currents in transformers you use ferrite instead of iron; because ferrite has higher resistance

The question wants 'most rapid heating'. Therefore you want high resistance to create more heat. End of Story.

 

[v1]

19. I got C too.. but after thinking about it.. THE electrical resistance must be HIGH, thus it provides more thermal energy, if it were low, the eddy current would take a while to warm dat shit up. feel me?

ideally saucepans are low resistance metals that are good conductors of heat
gl warming dat shit up with a high resistance plastic insulator haha

 

[mickstarify]

ideally saucepans are low resistance metals that are good conductors of heat
gl warming dat shit up with a high resistance plastic insulator haha

Read the first paragraph on wikipedia, https://en.wikipedia.org/wiki/Induction_cooking

In an induction cooker, a coil of copper wire is placed underneath the cooking pot. An alternating electric current flows through the coil, which produces an oscillating magnetic field. This field induces an electric current in the pot. Current flowing in the metal pot produces resistive heating which heats the food. While the current is large, it is produced by a low voltage.

 

[himynameisbrody]

Read the first paragraph on wikipedia, https://en.wikipedia.org/wiki/Induction_cooking

Whilst the coil in the cooktop may only use a low voltage, the question asked whether a high or low voltage frequency was used. Therefore, high.

 

[habitres]

Here are what I believe to be the correct answers (after consulting w/ teacher and fellow classmates)
1. D
2. A
3. C
4. B
5. C
6. C
7. B
8. A
9. B
10. D
11. C (I got D but it is C eh)
12. A
13. B
14. D
15. D (though in truth no statement is really correct)
16. C
17. B
18. C
19. D
29. B (We believe it is this as you only want to detect the wavelength that corresponds to its peak wavelength, if you had a low band gap (A) then it may detect other random radiation that won't distinguish it from humans etc)