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Probably an easy PHYSICS question but how do i do this?

Hello, this is from 2018 physics paper q13 , most should have the paper - how do you do this? the answer was B

The diagram shows an energy-level diagram for a hydrogen atom. Electrons, each having a kinetic energy of 2.0 × 10−18 J, collide with atoms of hydrogen in their ground state. Photons are emitted when the atoms de-excite. How many different wavelengths can be observed with incident electrons of this energy? [1 mark]
A 1
B
3
C 6
D 7
Reply 1
Avatar for Batman2k1
Batman2k1
OP
14
And also this one too - how i know the eq hf = o - ek, thats obv but must messed up calc somehow
Answer is A
Photons of wavelength 290 nm are incident on a metal plate. The work function of the
metal is 4.1 eV
What is the maximum kinetic energy of the emitted electrons?
[1 mark]
A 0.19 eV
B 4.3 eV
C 6.9 eV
D 8.4 eV
Original post by Batman2k1
Hello, this is from 2018 physics paper q13 , most should have the paper - how do you do this? the answer was B

The diagram shows an energy-level diagram for a hydrogen atom. Electrons, each having a kinetic energy of 2.0 × 10−18 J, collide with atoms of hydrogen in their ground state. Photons are emitted when the atoms de-excite. How many different wavelengths can be observed with incident electrons of this energy? [1 mark]
A 1
B
3
C 6
D 7


Cannot answer without the energy-level diagram.


Original post by Batman2k1
And also this one too - how i know the eq hf = o - ek, thats obv but must messed up calc somehow
Answer is A
Photons of wavelength 290 nm are incident on a metal plate. The work function of the
metal is 4.1 eV
What is the maximum kinetic energy of the emitted electrons?
[1 mark]
A 0.19 eV
B 4.3 eV
C 6.9 eV
D 8.4 eV


max KE = (3.0 x 10^8 x 6.63 x 10^-34)/(1.60 x 10^-19 x 290 x 10^-9) - 4.1 = 0.19 eV
Reply 3
Avatar for Batman2k1
Batman2k1
OP
14
here you go, not sure if the image is big, a noobie to this stuff.

2ND one u just did fq which i did * h, but divide by charge of electron? why?



2.JPG

Original post by BobbJo
Cannot answer without the energy-level diagram.




max KE = (3.0 x 10^8 x 6.63 x 10^-34)/(1.60 x 10^-19 x 290 x 10^-9) - 4.1 = 0.19 eV
2.JPG44.0KB
Original post by Batman2k1
here you go, not sure if the image is big, a noobie to this stuff.

2ND one u just did fq which i did * h, but divide by charge of electron? why?



2.JPG


E=hcλ E = \dfrac{hc}{\lambda}
gives the photon energy in joule
divide by electronic charge to get energy in eV

convert 2.0 x 10^-18 J to eV
2.0 x 10^-18 J is 12.5 eV

The electron in the ground state of the H atom will be excited to the -1.51 eV level.
The energy change corresponding to this is 13.6 - 1.51 = 12.1 eV
The kinetic energy of the electron which collided is 0.4 eV after the collision.

from the -1.51 eV level, it can de-excite to -3.4 eV then to -13.6 eV, or from -1.51 eV to -13.6 eV giving 3 photon wavelengths
Reply 5
Avatar for ben2600
ben2600
1
why will it be excited form the ground state to the -1.51 level?

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