View Full Version : Just took my final but I think there was an invalid question

MarinaHighTennis

12-07-2011, 05:09 PM

It was based upon spectrometry. So if you have a transmittance of 10 EU and an Absorbance of 2.0, what is Io (I initial) and T %?

Use the formulas: A=log(1/T), T=(I/Io), %T= (I/Io)x100, A=log(Io/I)

I did this then got stuck, but I answered T%= 1%

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https://picasaweb.google.com/lh/photo/Gga7k3pdoUq9JNyoAERRodMTjNZETYmyPJy0liipFm0?feat=d irectlink

Talker

12-07-2011, 06:37 PM

It was based upon spectrometry. So if you have a transmittance of 10 EU and an Absorbance of 2.0, what is Io (I initial) and T %?

Use the formulas: A=log(1/T), T=(I/Io), %T= (I/Io)x100, A=log(Io/I)

I did this then got stuck, but I answered T%= 1%

How do I post a picture larger?

https://lh6.googleusercontent.com/-DWeG2OolD_c/TuAcJhUvS_I/AAAAAAAAAno/INyZuCy1-Eo/s144/2011-12-07%25252006.04.33%252520pm.png

https://picasaweb.google.com/lh/photo/Gga7k3pdoUq9JNyoAERRodMTjNZETYmyPJy0liipFm0?feat=d irectlink

Isn't I( initial ) just set to 100? No matter what it is (I) would be a percentage of that if I'm looking at this right.

Good luck! :)

MarinaHighTennis

12-07-2011, 07:17 PM

Isn't I( initial ) just set to 100? No matter what it is (I) would be a percentage of that if I'm looking at this right.

Good luck! :)

Sounds logical, I wish our teacher told us that. Brainfuse didn't even know how to do this problem

I already took my final, but I was stuck on this question. :(

thug the bunny

12-08-2011, 05:41 AM

MHT, I think you are right, something is wrong with the question.

Transmittance should be unitless, either as a ratio <1, or as a percentage, not EU (is that Euros?). Absorbance is in units of AU (absorbance units). And, why ask what Io is, when it is always defined as 100%? Doesn't make sense...

MarinaHighTennis

12-08-2011, 07:30 AM

MHT, I think you are right, something is wrong with the question.

Transmittance should be unitless, either as a ratio <1, or as a percentage, not EU (is that Euros?). Absorbance is in units of AU (absorbance units). And, why ask what Io is, when it is always defined as 100%? Doesn't make sense...

I hope the teacher didn't screw us over for the final, but EU is energy units so its not really a unit of measurement.

It was based upon spectrometry. So if you have a transmittance of 10 EU and an Absorbance of 2.0, what is Io (I initial) and T %?

Use the formulas: A=log(1/T), T=(I/Io), %T= (I/Io)x100, A=log(Io/I)

I did this then got stuck, but I answered T%= 1%

I’m very sorry, but IMO your answer is not exactly right.

By definition , see please http://en.wikipedia.org/wiki/Transmittance ,transmittance is

T=Iout/Iin (1)

where Iin is the intensity of the incident radiation and Iout is the intensity of radiation coming out of the sample.

The absorbance is

A=Log(Iin/Iout) (2)

We know that Iout = 10 EU and A = 2.

From (2) we have

Iin / Iout = 10** A = 10**2=100.

Thus T = 1/100 =1%

From (1)

Iin = Iout*100 = 1000 EU

:confused:

How do I post a picture larger?

https://lh6.googleusercontent.com/-DWeG2OolD_c/TuAcJhUvS_I/AAAAAAAAAno/INyZuCy1-Eo/s144/2011-12-07%25252006.04.33%252520pm.png

https://picasaweb.google.com/lh/photo/Gga7k3pdoUq9JNyoAERRodMTjNZETYmyPJy0liipFm0?feat=d irectlink

http://i40.tinypic.com/v4pkrp.png

MarinaHighTennis

12-08-2011, 10:26 AM

I’m very sorry, but IMO your answer is not exactly right.

By definition , see please http://en.wikipedia.org/wiki/Transmittance ,transmittance is

T=Iout/Iin (1)

where Iin is the intensity of the incident radiation and Iout is the intensity of radiation coming out of the sample.

The absorbance is

A=Log(Iin/Iout) (2)

We know that Iout = 10 EU and A = 2.

From (2) we have

Iin / Iout = 10** A = 10**2=100.

Thus T = 1/100 =1%

From (1)

Iin = Iout*100 = 1000 EU

:confused:

Thanks for the help but one thing that puzzled me is that If A= log(1/T) and T=10 it comes out to be -1. Do we ignore the T=10?

Thanks for the help but one thing that puzzled me is that If A= log(1/T) and T=10 it comes out to be -1. Do we ignore the T=10?

According to definition T=Iout/Iin.

Thus, T is always less or equal to 1 (0<T<1).

In your case: T=0.01=1%, Iout=10 EU, and Iin =1000 EU.

If T=1/100 than 1/T=100 and A=log(1/T)=log(100)=2.

EU is complicated energy unit.

BaboFan

12-08-2011, 04:28 PM

According to definition T=Iout/Iin.

Thus, T is always less or equal to 1 (0<T<1).

In your case: T=0.01=1%, Iout=10 EU, and Iin =1000 EU.

If T=1/100 than 1/T=100 and A=log(1/T)=log(100)=2.

EU is complicated energy unit.

Correct me if I'm wrong but isn't 2 Max absorbtion? So t is? 0% and I 0

Correct me if I'm wrong but isn't 2 Max absorbtion? So t is? 0% and I 0

If (0<T<1) than (∞>1/T>1)

A=log(1/T)

If 1/T=1 than A= log(1)=0

If 1/T=∞ than A=log(∞)=∞

So, (0<A<∞)

and Amax=∞

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