Aproton is placed at point a, where the electric potential is 100 v . the proton is released from rest. some time later, the proton has reached point b, where the electric potential is -120 v . what is the de broglie wavelength of the proton when it reaches point b?

To develop this problem it is necessary to apply the concepts related to electromagnetic energy and Broglie's hypothesis.

By definition we know that the electrical energy of a proton can be expressed as

E = qV

Where,

q = Charge of proton

V = Voltage

Replacing with our values

E = qV

It is necessary to add the two potentials

From Broglie's hypothesis we know that the wavelength is given by

Where,

h = Planck's constant

p = Momentum

The momentum of a particle can be expressed in terms of energy, that is,

Where,

m = mass

E = Energy (potential or kinetic)

Therefore replacing this value at lambda,

protons in

real, smaller and upside-down.   so the answer should be b.