Atomic Models

Step 1: Calculate the energy of the absorbed photon:
The energy of the photon is given by the equation ,
where:
(Planck's constant),
(speed of light),
(wavelength of the photon).
Substitute the values:
.

Step 2: Calculate the momentum of the absorbed photon:
The momentum of a photon is given by the equation .
Substitute the values:
.

Step 3: Use the conservation of momentum to find the change in velocity of the He atom:
The momentum change of the He atom is equal to the momentum of the photon.
The mass of a helium atom is .
Since momentum is conserved:
.

Step 4: Final Answer:
The change in the velocity of the He atom after the photon absorption is 30 cm/s.