The following table gives the length, diameter and applied potential difference of four copper wires, A, B, C and D, across their ends. Arrange the wires in correct order of the increasing electric field.
| Length | Diameter | Potential difference | |
| (A) Wire A | \( l \) | \( 3d \) | \( V \) |
| (B) Wire B | \( 2l \) | \( d \) | \( V \) |
| (C) Wire C | \( 3l \) | \( 2d \) | \( 2V \) |
| (D) Wire D | \( 3l \) | \( 2d \) | \( V \) |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (D), (B), (C), (A)
Inside a uniform wire the electric field is the potential difference per unit length, \( E = V/l \). The diameter does not enter: it changes the resistance and the current, but not the field.
\( E_A = V/l \)
\( E_B = V/2l = 0.5\,V/l \)
\( E_C = 2V/3l \approx 0.67\,V/l \)
\( E_D = V/3l \approx 0.33\,V/l \)
\( E_D \lt E_B \lt E_C \lt E_A \)
The increasing order is D, B, C, A.