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### Test #2: Q6

Posted: **Sun Apr 29, 2018 11:48 am**

by **Gabi Landes 1-H**

I got the second part of this question incorrect, I am assuming because of an accident when inputting the numbers into my calculator.

I have re-done the problem below and just want to make sure I am on the right track.

Q6. Microwave ovens use microwave electromagnetic radiation to cause vibrations within the molecules in food causing it to heat it up. Microwave radiation has a frequency of about 3x10^9 Hz. Determine the energy, in J, and the wavelength, in nm, of a microwave. E=hv

E=(6.62608x10^-34 J*s)(3x10^9 s^-1)

E=2x10^-24 J

=c/v (from c=

v)

= (2.99792x10^8 m*s^-1)/(3x10^9 s^-1)x(1 nm)/10^-9 m)

=9.99306667x10^-7 nm

= 10x10^-7 nm

### Re: Test #2: Q6

Posted: **Sun Apr 29, 2018 2:52 pm**

by **FizaBaloch1J**

When I did this problem to find wavelength I used wavelength= ch/E instead.

### Re: Test #2: Q6 [ENDORSED]

Posted: **Sun Apr 29, 2018 4:04 pm**

by **Megan Potter 1G**

I also used wavelength=hc/E, but the way you do it works too. With rounding the answer is 10 x 10^7 (positive exponent of 7, not negative, because there's 10^9 nanometers in one meter)

### Re: Test #2: Q6

Posted: **Sun Apr 29, 2018 5:24 pm**

by **Elena 1H**

I initially used the derived equation λ=hc/E but I realized it was easier to just use λ=c/v because all the values are given to you, but yes you are on the right track

### Re: Test #2: Q6

Posted: **Sun Apr 29, 2018 7:10 pm**

by **Emely Reyna 1F**

I also used both E=hv and wavelength= c/v and came up with the same answer but using wavelength= hc/E is quicker and would result in less calculator error.

### Re: Test #2: Q6

Posted: **Sun Apr 29, 2018 8:02 pm**

by **Myles Chang 1B**

I think this is most likely just a calculator error. You should get the same answer regardless of what equation you use.

### Re: Test #2: Q6

Posted: **Sun Apr 29, 2018 9:12 pm**

by **Samantha Castro 1D**

In addition, I also used E=hv and wavelength=c/v and came up with the same answer. But also using wavelenght=hc/E can work as well.

### Re: Test #2: Q6

Posted: **Tue May 01, 2018 9:00 pm**

by **Gabi Landes 1-H**

Megan Potter 1G wrote:I also used wavelength=hc/E, but the way you do it works too. With rounding the answer is 10 x 10^7 (positive exponent of 7, not negative, because there's 10^9 nanometers in one meter)

If you don't mind explaining more, just so I can possibly understand, why would 10^9 nanometers in one meter make the answer positive?

### Re: Test #2: Q6

Posted: **Wed May 02, 2018 5:32 pm**

by **Paywand Baghal**

Gabi Landes 1-H wrote:Megan Potter 1G wrote:I also used wavelength=hc/E, but the way you do it works too. With rounding the answer is 10 x 10^7 (positive exponent of 7, not negative, because there's 10^9 nanometers in one meter)

If you don't mind explaining more, just so I can possibly understand, why would 10^9 nanometers in one meter make the answer positive?

Yes if possible could you explain? I am pretty sure 1 x 10^-9 m is 1 nm not positive 9

### Re: Test #2: Q6

Posted: **Thu May 03, 2018 10:31 pm**

by **Megan Potter 1G**

So if you solve the equation you get this:

Wavelength = {(6.626 x 10^-34)(2.998 x 10^8)}/(1.99 x 10^-24)

wavelength = .099821 meters

there are 10^9 nanometers in one meter (nanometers are smaller so it makes sense that there should be a ton of them to make one meter)

using dimensional analysis to convert:

.099821 meters x (10^9 nm)/1m = 9.982 x 10^7 nm as the wavelength

hope this helps! let me know if there's something else I can explain

### Re: Test #2: Q6

Posted: **Thu May 03, 2018 10:32 pm**

by **Megan Potter 1G**

Paywand Baghal wrote:Gabi Landes 1-H wrote:Megan Potter 1G wrote:I also used wavelength=hc/E, but the way you do it works too. With rounding the answer is 10 x 10^7 (positive exponent of 7, not negative, because there's 10^9 nanometers in one meter)

If you don't mind explaining more, just so I can possibly understand, why would 10^9 nanometers in one meter make the answer positive?

Yes if possible could you explain? I am pretty sure 1 x 10^-9 m is 1 nm not positive 9

see my explanation above but yes you are right, 1x10^-9 m = 1nm, so 1x10^9 nm=1 m :)