For the arrangement of the potentiometer shown in the figure, the balance point is obtained at a...

For the arrangement of the potentiometer shown in the figure, the balance point is obtained at a distance \( 75 \mathrm{~cm} \) from \( A \) when the key \( k \) is open.

The second balance point is obtained at \( 60 \mathrm{~cm} \) from \( A \) when the key \( k \) is closed. Find the internal resistance of the battery \( E_{1} \).
(A) \( 1.5 \Omega \)
(B) \( 2 \Omega \)
(C) \( 0.5 \Omega \)
(D) \( 1 \Omega \)