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

1. Jan 11, 2005

### Lorax

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)

2. Jan 12, 2005

### meteor

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

Last edited: Jan 12, 2005
3. Jan 12, 2005

### dextercioby

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...

Daniel.

4. Jan 12, 2005

### Lorax

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 heres 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. Jan 12, 2005

### dextercioby

148.By the looks of it,the transformation of units is wrong.
$$1MeV=10^{6}\cdot 1.6 \cdot 10^{-19}C\cdot 1V=1.6\cdot 10^{-13}J$$

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. Jan 12, 2005

### Lorax

our book does little to no justice for the section, and gives a half a page of uninsightful babble.

7. Jan 12, 2005

### dextercioby

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. Jan 13, 2005

### Lorax

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. Jan 13, 2005

### dextercioby

145 is obviously wrong,mathematically.You reached an equation
$$36=n^{2}$$ 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. Jan 13, 2005

### Lorax

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?

Last edited: Jan 13, 2005
11. Jan 13, 2005

### dextercioby

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. Jan 13, 2005

### Lorax

is the antineutrino just +0/0? Is that all I have to add?

13. Jan 13, 2005

### dextercioby

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

Daniel.

14. Jan 13, 2005

### Lorax

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. Jan 13, 2005

### dextercioby

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

Daniel.

16. Jan 13, 2005

### Lorax

Freq of ligh= hc/E

(6.63x10^-34)(3x10^8)/(6.25x10^3)(1.6x10^-19) = 1.89.x10^-10m

17. Jan 13, 2005

### dextercioby

Light is made up of photons,not electrons... U can't apply that formula.You need the formula of Louis de Broglie...

Daniel.

18. Jan 13, 2005

### Lorax

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. Jan 13, 2005

### dextercioby

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. Jan 13, 2005

### Lorax

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?