Consider a beam of electrons with energy 1 eV, flying exactly in x-direction (i.e. no momentum in y-direction, py=0). You now measurethe y-position of the electrons by placing an aperture with 5 nm widthinto the beam. What is the consequence? y

x(A) I now know the y-position of the electrons within 5 nm. The electrons continue straight on along the x-direction, just like before the measurement.

(B) I now know the y-position of the electrons within 5 nm. Some of the electrons are deflected and acquire some momentum in y-direction, now flying faster than before.

(C) I now know the y-position of the electrons within 5 nm. Some of the electrons are deflected and acquire some momentum in y-direction, slowing down accordingly w.r. to their momentum along x-direction.

Consider a beam of electrons with energy exactly 1 eV, flying exactly in x-direction (i.e. no momentum in y-direction, py=0). You now measurethe y-position of the electrons by placing an aperture with 5 nm widthinto the beam. What is the consequence? y

x(A) I now know the y-position of the electrons within 5 nm. The electrons continue straight on along the x-direction, just like before the measurement.

(B) I now know the y-position of the electrons within 5 nm. Some of the electrons are deflected and acquire some momentum in y-direction, now flying faster than before.

(C) I now know the y-position of the electrons within 5 nm. Some of the electrons are deflected and acquire some momentum in y-direction, slowing down accordingly w.r. to their momentum along x-direction.

Before slit: py = 0 we do not know the y-position of the electrons at all!... y =

After slit: y = 5 nm py = ħ/10 nm .... we cannot circumvent HUP!

Note: The slit results in diffraction of the matter wave, whichintroduces the uncertainty in py as shown below. You already knowthis behavior from diffraction of light at a slit!

y

x

screen

The conservation of total mechanical energy of a frictionless particle means that …

(A) … the sum of heat and kinetic energy is a constant.

(B) … the potential energy of the system is a constant.

(C) … the sum of kinetic and potential energy is a constant.

(D) … the particle has always the same velocity.

The conservation of total mechanical energy of a frictionless particle means that …

(A) … the sum of heat and kinetic energy is a constant.

(B) … the potential energy of the system is a constant.

(C) … the sum of kinetic and potential energy is a constant.

(D) … the particle has always the same velocity.