In the straight wire A, current is flowing in the vertically downward direction whereas in wire B the current is flowing in the vertically upward direction. What is the direction of magnetic field :
(a) in wire A ?
(b) in wire B ?
Name the rule which you have used to get the answer.

Explanation

To solve the problem regarding the direction of the magnetic field around two straight wires carrying current in opposite directions, we can use the Right-Hand Thumb Rule (also known as the Maxwell's Right-Hand Rule). Here’s a step-by-step solution:

### Step 1: Understand the Current Directions
- In wire A, the current is flowing in the vertically downward direction.
- In wire B, the current is flowing in the vertically upward direction.

### Step 2: Apply the Right-Hand Thumb Rule for Wire A
- For wire A, point your thumb downward (in the direction of the current).
- Your fingers will curl around the wire. The direction in which your fingers curl represents the direction of the magnetic field.
- As your fingers curl around wire A, they will move in a clockwise direction when viewed from above.

**Conclusion for Wire A:** The direction of the magnetic field around wire A is clockwise.

### Step 3: Apply the Right-Hand Thumb Rule for Wire B
- For wire B, point your thumb upward (in the direction of the current).
- Your fingers will again curl around the wire. The direction in which your fingers curl represents the direction of the magnetic field.
- As your fingers curl around wire B, they will move in an anti-clockwise direction when viewed from above.

**Conclusion for Wire B:** The direction of the magnetic field around wire B is anti-clockwise.

### Step 4: State the Rule Used
- The rule used to determine the direction of the magnetic field is the Right-Hand Thumb Rule (Maxwell's Right-Hand Rule).

### Final Answers:
(a) The direction of the magnetic field in wire A is clockwise.
(b) The direction of the magnetic field in wire B is anti-clockwise.
Rule used: Right-Hand Thumb Rule.

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