Question

An electric current passes through a straight wire. The direction of magnetic field at the points $A$ and $B$ will be :

• A. Same
• B. Opposite
• C. depends on the magnitude of current in wire
• D. can't be determined.

Answer 1

The correct option is B Opposite

From the maxwell's right hand thumb rule if the thumb is placed in direction of current then the direction of curl suggests that the fingers are going verically downwards at point $B,$ and vertically upwards at point ${}^{\prime }{A}^{\prime }$.

Here $\odot$ represents field lines coming out of plane of paper and $⨂$ represents field is opposite at ${}^{\prime }{A}^{\prime }$ and ${}^{\prime }{B}^{\prime }$, thus directions of magnetic field will be opposite at $A$ and $B$.