Part B: Shoe your reasoning and unit conversions clearly and completely. Energy

Question

Part B: Shoe your reasoning and unit conversions clearly and completely. Energy and momentum. Use words, not equations, to difine an electron-Volt (eV). Then show that I eV = 1.6 times 10^-10 J, include units. When is the kinetic energy, in eV, of a proton that has been accelerated from rest over a potential difference of 100 kV (meaning = 100 kV)? What is its momentum? What is the kinetic energy, in eV, of an electron that has been accelerated over the same potential difference in the opposite direction, + 100 kV? What is its momentum?

Explanation / Answer

a) One electron volt is defined as the energy needed to move an electron (which has an electric charge equal to -1) across an electric potential of one volt.

1 eV = 1.6*10^-19 C* 1V = 1.6*10^-19 J

B) KE + PE = constant

potential energy is decreased by 1e*100 kV = 10^5 eV

So kinetic energy has to be increased from 0 to 10^5 eV

KE = 10^5 eV

MOMENTUM = sqrt(2mKE) = sqrt(2*1.673*10^-27*1.6*10^-19*10^5)

= 7.316*10^-21 kgm/s

c)KE + PE = constant

potential energy is increased by -1e*100 kV = -10^5 eV

potential energy is decreased by 10^5 eV

So kinetic energy has to be increased from 0 to 10^5 eV

KE = 10^5 eV

MOMENTUM = sqrt(2mKE) = sqrt(2*9.1*10^-31*1.6*10^-19*10^5)

=1.706*10^-22 kgm/s

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