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Question -

The total energy of an electronin the first excited state of the hydrogen atom is about −3.4 eV.

(a) What isthe kinetic energy of the electron in this state?

(b) Whatis the potential energy of the electron in this state?

(c) Which ofthe answers above would change if the choice of the zero of potential energy ischanged?



Answer -

(a) Totalenergy of the electron, E = −3.4 eV

Kinetic energy of the electron isequal to the negative of the total energy.

K = −E

= − (− 3.4) = +3.4 eV

Hence, the kinetic energy of theelectron in the given state is +3.4 eV.

(b) Potentialenergy (U) of the electron is equal to the negative of twice of itskinetic energy.

U =−2 K

= − 2 × 3.4 = − 6.8 eV

Hence, the potential energy ofthe electron in the given state is − 6.8 eV.

(c) Thepotential energy of a system depends on the reference point taken. Here, thepotential energy of the reference point is taken as zero. If the referencepoint is changed, then the value of the potential energy of the system alsochanges. Since total energy is the sum of kinetic and potential energies, totalenergy of the system will also change.

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