Question

Two parallel wires carrying current in the same direction attract each other because of

• A. potential difference between them
• B. mutual inductance between them
• C. electric forces between them
• D. magnetic forces between them

Answer 1

The correct option is D magnetic forces between them

Force on a current carrying conductor is $F=\int i(\overrightarrow{dl}\times \overrightarrow{B})$
Magnetic field due to one wire at the location of the second wire ( other one ) is $B_1=\frac{{\mu }_0{i}_1}{2\pi d}$
Forceon the 2nd wire due to $B_1$ is $F_{21}=i_2{l}_2{B}_1=i_2{l}_2\frac{{\mu }_0{i}_1}{2\pi d}=\frac{{\mu }_0{i}_1{i}_2{l}_2}{2\pi d}$
Force per unit length for wire $l_2$ is $F_{perunitlength}=\frac{F_{21}}{l_2}$
The force is attractive.