What is the wavelength of a photon that has energy of 2.10eV

I'm going to do a little more work here.In summary, the conversation was about homework questions related to various physics problems involving magnetic fields, photons, and nuclear reactions. The student requested help with a few questions and provided some of their own work for feedback. They were able to solve some of the problems, but still needed help with others. They were also unsure about the correct nuclear reactions for two problems.
  • #1
Lorax
42
0
Last Homework questions of the year! whoo! I'm having troubles with these so if you could help me out. I'm working on the bottom to the top, so if you want to help, help with 116 and down.


116. A proton travels through a magnetic field at the speed of 6.3 x 10^4 m/s perpendicular to the field. If the radius of the arc pf the deflected proton is 7.20x10^-3, what is the magnetic field strength?


122. A proton moves through a 0.06 T magnetic field in a circle with aradius of 0.30 m. What is the momentum of this proton?

124. What is the wavelength of a photon that has energy of 2.10eV

128. Electrons are ejected from a photoelectric surface with a maximum speed of 3.8 x 10^5 m/s. If the work function of this surface is 2.55 eV, what is the wavelength of the incident light?

130. What is the operating potential of an x-ray tube if photons with a maximum energy of 6.43x10^-15 J are produced?

140. An Electron endergoes a transition from the 6th energy level to the 2nd energy level in a hydrogen atom. What is the frequency of the light emitted?

145. What orbit (n value) in a hydrogen atom has a radius of 1.90 x 10^-19

146. If the momentum of a photon is 8.6 x 10 ^ -22 kg m/s what is its speed?

148. Calculate the wavelength of an electron that has kinetic energy of 6.25x10^-3 MeV.

164. Write the nuclear reaction for the alpha decay of uranium - 238.

165. Write the nuclear reaction for the beta decay (emission of an electron by the nucleus) of cobalt 60.

180. If the binding energy of lithium -6 (6/3Li) nucleus is 4.9118 x 10 ^-12 J, what is the mass of the nucleus? (mass of proton = 1.6726 x 10^-27 kg, mass of a neutron = 1.6749 x 10 ^-27 kg)
 
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  • #2
Ok, only the 3 first...

116) B=m*v/q*R=(1.6*10-27 kg*6.3*104m/s)/(1.6*10-19 C*7.2*10-3 m)= 0.08 T

122) Momentum=m*v . Then using the anterior formula we get the velocity... v=B*q*R/m= 1.75*106 m/s. So momentum is=2.8*10-21 Kg*m/s

124) Energy=h*f. Then, f=6.6*10-34/3'36*10-19J (I have passed from eV to Joules)=1.96*10-15 Hz.
f*wavelength=c, so wavelenght=f/c=6.53*10-24 m
 
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  • #3
NO,nonononono... :grumpy: Don't solve his homework... :grumpy: Let him do it himself.Ask him what has gone wrong,invite him to post his work and questions...

Read the "sticky"...


Daniel.
 
  • #4
Okay let me start off...

116. A proton travels through a magnetic field at the speed of 6.3 x 10^4 m/s perpendicular to the field. If the radius of the arc pf the deflected proton is 7.20x10^-3, what is the magnetic field strength?

Thanks.

122. A proton moves through a 0.06 T magnetic field in a circle with aradius of 0.30 m. What is the momentum of this proton?

Thanks.

124. What is the wavelength of a photon that has energy of 2.10eV

Thanks.

Okay here's some of my work now...

128. Electrons are ejected from a photoelectric surface with a maximum speed of 3.8 x 10^5 m/s. If the work function of this surface is 2.55 eV, what is the wavelength of the incident light?

I did E=hc/frequency and got 6.175 x10^-10. Look good?


130. What is the operating potential of an x-ray tube if photons with a maximum energy of 6.43x10^-15 J are produced?

Working on this one currently will post later.

140. An Electron endergoes a transition from the 6th energy level to the 2nd energy level in a hydrogen atom. What is the frequency of the light emitted?

For this one I did...

1/Frequency=RH(1/n^2-1/n^2), then took that into E=hc/frequency then took that into F=E/h to get -3.913x10^25 but now I'm thinking I did to many steps and should have stuck with just... 4.09x10^-7. Look good?

145. What orbit (n value) in a hydrogen atom has a radius of 1.90 x 10^-19

Troubles with this one, a starting position would be nice.

146. If the momentum of a photon is 8.6 x 10 ^ -22 kg m/s what is its speed?

I'm working on this one to, my mind just blanked at how to get the mass of a photon but I will get this one.

148. Calculate the wavelength of an electron that has kinetic energy of 6.25x10^-3 MeV.

For this...

I converted the meV to 1x10^-15J, then put that into V=(Square root) 2ek/m, then I did p=mv, then P=h/frequency to get 4.911 x 10 ^ -4


164. Write the nuclear reaction for the alpha decay of uranium - 238.

I NEED MAJOR HELP WITH THIS ONE. Totally clueless.

165. Write the nuclear reaction for the beta decay (emission of an electron by the nucleus) of cobalt 60.

Same as 164.
180. If the binding energy of lithium -6 (6/3Li) nucleus is 4.9118 x 10 ^-12 J, what is the mass of the nucleus? (mass of proton = 1.6726 x 10^-27 kg, mass of a neutron = 1.6749 x 10 ^-27 kg)

Currently looking over this, I may need help.

So if you could look over my work, and maybe help me with the ones left that would be great.
 
  • #5
148.By the looks of it,the transformation of units is wrong.
[tex] 1MeV=10^{6}\cdot 1.6 \cdot 10^{-19}C\cdot 1V=1.6\cdot 10^{-13}J[/tex]

As for the nuclear physics problems,try to think about what happens in a disintegration of type "beta".Your book might provide some help.


Daniel.
 
  • #6
our book does little to no justice for the section, and gives a half a page of uninsightful babble.
 
  • #7
Lorax said:
our book does little to no justice for the section, and gives a half a page of uninsightful babble.

Still i can't give you the reactions,u need to figure them out yourself.What are the atomic and the mass numbers of the isotope of Cobalt 60??What does losing an electron assume,in relation to these numbers.??

Daniel.
 
  • #8
I think I might have figured em out, anyways how about the ones I posted so far do they look right?

and then...

145.

r2 = r1n^2
r2/r1=n^2

1.90x10^-9/5.29x10^-11=n^2

36=n^2

n=36?

Look good?

146.

Is it just 3.00x18^8 m/s? Simply more of a knowledge question?

164.

234/90Th+4/2a?

165.

60/28 Ni + 0/-1B?

180.

I need help with this one, can someone help me with the proton and electron count and how you came up with that? I'm brutal at chem. I think I can do the rest by applying m=E/c^2.
 
  • #9
145 is obviously wrong,mathematically.You reached an equation
[tex] 36=n^{2} [/tex] which u need to solve,knowing that u need only the positive integer solution.

146.It's wrong,By the looks of it,it's more than the speed of light... :tongue2:

164 is correct.

165.is incomplete.U miss a reaction product.A particle.

Daniel.
 
  • #10
145. I miss typed that it should be 6
146. umm did I just miss type again on it? it should be 3.00x10^8m/s
164.woo
165. I'm onsure about the reaction product I am missing, more help?

Can you also help me out with 180?
 
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  • #11
Lorax said:
145. I miss typed that it should be 6
146.working on it
164.woo
165. I'm onsure about the reaction product I am missing, more help?

Can you also help me out with 180?


Yes,u need to know the need to know the formula giving the bond energy as a function between the nucleus mass (tabulated quantity) and the masses of nucleons (protons and neutrons).
Look for it in the book.

Daniel.

PS.An electron antineutrino.It's always there in a beta decay.
 
  • #12
is the antineutrino just +0/0? Is that all I have to add?
 
  • #13
Lorax said:
is the antineutrino just +0/0? Is that all I have to add?

Yes,an antineutrino is (in the original version of theory) a massless particle and without electric charge.

Daniel.
 
  • #14
148. Calculate the wavelength of an electron that has kinetic energy of 6.25x10^-3 MeV.

Which of these answers is right... I did two different equations cause I was unsure...

1.89x10^-10 or 6.21x10^10?
 
  • #15
Lorax said:
148. Calculate the wavelength of an electron that has kinetic energy of 6.25x10^-3 MeV.

Which of these answers is right... I did two different equations cause I was unsure...

1.89x10^-10 or 6.21x10^10?

The second number is completely wrong.Show how u've gotten the first one.

Daniel.
 
  • #16
Freq of ligh= hc/E

(6.63x10^-34)(3x10^8)/(6.25x10^3)(1.6x10^-19) = 1.89.x10^-10m
 
  • #17
Light is made up of photons,not electrons... :wink: U can't apply that formula.You need the formula of Louis de Broglie...

Daniel.
 
  • #18
Okay and for question 180...

A person on a cpu game told me I should start out with 3 protons and 3 neutrons. Can you tell me why that is? I could just do the question but I want to know why.

180. If the binding energy of lithium -6 (6/3Li) nucleus is 4.9118 x 10 ^-12 J, what is the mass of the nucleus? (mass of proton = 1.6726 x 10^-27 kg, mass of a neutron = 1.6749 x 10 ^-27 kg)
 
  • #19
U take a nucleus.It has a rest mass "M".And then u know that this nucleus is made up (esentially) of protons and electrons.Compute the mass of the nucleus using the values for Z and A.It will never equal "M".The difference between these 2 figures is just the bond energy/c^{2}.

Daniel.
 
  • #20
dextercioby said:
Light is made up of photons,not electrons... :wink: U can't apply that formula.You need the formula of Louis de Broglie...

Daniel.

Hmm okay let met think...

v=(square root) 2E/m

then I do

Wavelength = h/mv.

so I get... 4.686x10^21 as my velocity

and then 1.55 x 10 ^-25 as my answer. Is that better?
 
  • #21
dextercioby said:
U take a nucleus.It has a rest mass "M".And then u know that this nucleus is made up (esentially) of protons and electrons.Compute the mass of the nucleus using the values for Z and A.It will never equal "M".The difference between these 2 figures is just the bond energy/c^{2}.

Daniel.


Yes but why is it 3 protons and 3 neutrons? How do you figure that out? I've been sick and missed some classes.

Also I did it now using 3 of each, and got... 9.98x10^-27kg
 
  • #22
Lorax said:
Hmm okay let met think...

v=(square root) 2E/m

then I do

Wavelength = h/mv.

so I get... 4.686x10^21 as my velocity

and then 1.55 x 10 ^-25 as my answer. Is that better?


Good formulas,bad numbers.Are u sure u're using the right figures and units...??

Daniel.
 
  • #23
Lorax said:
Yes but why is it 3 protons and 3 neutrons? How do you figure that out? I've been sick and missed some classes.

Also I did it now using 3 of each, and got... 9.98x10^-27kg

Because it is a nucleus of [tex] ^{6}_{3}Li [/tex].It has Z=3 and A=6.Can u figure out the numbers of each particles inside it??

Daniel.
 
  • #24
dextercioby said:
Good formulas,bad numbers.Are u sure u're using the right figures and units...??

Daniel.


Hmm I think it has to maybe do with my MeV conversion.

Its 6.25x10^-3 MeV's, I converted it to 6.25x10^3 eV. Then I converted that into J's by multiplying it by 1.6x10^-19 to get 0.735.

I then multiplied that by 2 = 1.47 then divided that by 9.11x10^31 to get 1.6136x10^30. Then I took the square root of that. 1.27x10^15.

So V=1.27x10^15.

this time I get 5.73 x 10 ^ -19 as the answer...

Where am I going wrong.
 
  • #25
Lorax said:
Hmm I think it has to maybe do with my MeV conversion.

Its 6.25x10^-3 MeV's, I converted it to 6.25x10^3 eV. Then I converted that into J's by multiplying it by 1.6x10^-19J/eV to get 0.735.

I then multiplied that by 2 = 1.47 then divided that by 9.11x10^31 to get 1.6136x10^30. Then I took the square root of that. 1.27x10^15.

So V=1.27x10^15.

this time I get 5.73 x 10 ^ -19 as the answer...

Where am I going wrong.

I've made remarks in your post.See above in the quote.
Bold:correct.
Blue:my notes.
Magenta:wrong.

Daniel.
 
  • #26
1.48x10^26?
 
  • #27
Don't give me a figure...Give me the whole calculations.Else,how am i suppodes to know whether a (presumably) correct result was obtained by a wrong method??

I guess you answer is wrong...Please put units to numbers...In this case "meters".

Daniel.
 
  • #28
I've spent 2 hours+ on this ridiciously easy question. I'm doing something wrong, don't you think you could help me out just a bit more then what you've been giving me? I know you know where I went wrong, and can see it just like that, but please have mercy on my brain.
 
  • #29
:rofl: Okay,
[tex] \lambda=\frac{h}{p} [/tex] (1)

[tex] p=\sqrt{2mE} [/tex] (2)

[tex] \lambda=\frac{h}{\sqrt{2mE}} [/tex](3)

[tex] h\sim 6.6 \cdot 10^{-34}J.s [/tex] (4)

[tex] m\sim 9.1\cdot 10^{-31} Kg [/tex] (5)

[tex] E\sim 6.25\cdot 1.6\cdot 10^{3}\cdot 10^{-19} J =10^{-15}J [/tex](6)

Plug (4),(5),(6) into (3).And get your result.

Daniel.
 

1. What is the relationship between energy and wavelength of a photon?

The energy of a photon is directly proportional to its wavelength. This means that as the energy of a photon increases, its wavelength decreases. Similarly, as the energy decreases, the wavelength increases.

2. How is the energy of a photon measured?

The energy of a photon is typically measured in electron volts (eV), which is a unit of energy commonly used in atomic and molecular physics. It is equal to the amount of energy gained by an electron when it moves through a potential difference of 1 volt.

3. How can the wavelength of a photon be calculated from its energy?

The relationship between energy and wavelength of a photon can be described by the equation E = hc/λ, where E is the energy of the photon, h is Planck's constant, c is the speed of light, and λ is the wavelength. Therefore, to calculate the wavelength, we can rearrange the equation to λ = hc/E.

4. What is the significance of 2.10eV in the given question?

The value of 2.10eV represents the energy of the photon in electron volts. This is equivalent to approximately 3.36 x 10^-19 joules. It is a commonly used unit for measuring the energy of photons and other particles in atomic and molecular physics.

5. How does the wavelength of a photon with an energy of 2.10eV compare to other wavelengths in the electromagnetic spectrum?

The wavelength of a photon with an energy of 2.10eV falls within the range of the visible light spectrum. This range of wavelengths extends from approximately 380 nanometers (violet) to 750 nanometers (red). Therefore, a photon with an energy of 2.10eV would have a wavelength somewhere within this range.

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