CUET · PHYSICS · PYQ PAPER 2023

The kinetic energy of an electron in the ground state of hydrogen atom is \(1 3 . 6 ~ e V\). The potential energy (P.E) and total energy ( E ) of electron in this state is :

A \(P . E=-13.6 eV , E=27.2 eV\)
B \(P . E=+13.6 eV , E=-27.2 eV\)
C \(P . E =+27.2 eV , E =-13.6 eV\)
D \(P \cdot E=-27.2 eV , E=-13.6 eV\)

Verified Solution

Answer & Solution

Correct Answer

(D) \(P \cdot E=-27.2 eV , E=-13.6 eV\)

Step-by-step Solution

Detailed explanation

\(P.E = -2 \times K.E = -2 \times 13.6 \, eV = -27.2 \, eV\) \(E = -K.E = -13.6 \, eV\)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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List-I (Quantity)	List-II (Formula)
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(B) De-Broglie Wavelength	(II) \( K_{max} = hc/\lambda - \phi \)
(C) Stopping potential	(III) \( hc/\phi \)
(D) Threshold wavelength	(IV) \( h/p \)

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(C) Fibrous proteins.	(III) Quaternary structure of proteins.
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Match List-I with List-II
Consider two vectors \(\vec{a}=\hat{i}+2 \hat{j}-\hat{k}\) and \(\vec{b}=-3 \hat{i}-6 \hat{j}+3 \hat{k}\).

List-I	List-II
(A) Angle between \(\vec{a}\) and \(\vec{b}\)	(I) \(\cos ^{-1}\left(\frac{1}{\sqrt{6}}\right)\)
(B) Angle between \(\vec{a}\) and \(x\)-axis	(II) \(\cos ^{-1}\left(\frac{2}{\sqrt{6}}\right)\)
(C) Angle between \(\vec{b}\) and \(x\)-axis	(III) \(\pi\)
(D) Angle between \(\vec{a}\) and \(y\)-axis	(IV) \(\cos ^{-1}\left(-\frac{1}{\sqrt{6}}\right)\)

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