Which is the only vector quantity out of the following ?

Options

A. Current flowing in a metal
B. Electrostatic potential
C. Charge of a gold leaf electroscope
D. Moment of a spinning body

Answer

To determine which of the given options is the only vector quantity, we will analyze each option step by step.

### Step 1: Analyze the first option - Current flowing in a metal
- **Explanation**: Current is defined as the flow of electric charge. While it has a magnitude (the amount of charge flowing per unit time), it does not have a specific direction in the same way that vector quantities do. Current can flow in different directions, but it is typically treated as a scalar quantity in many contexts.
- **Conclusion**: Current is not a vector quantity.

### Step 2: Analyze the second option - Electrostatic potential
- **Explanation**: Electrostatic potential is defined as the work done per unit charge. Since work is a scalar quantity, and charge is also a scalar, the electrostatic potential is also a scalar quantity.
- **Conclusion**: Electrostatic potential is not a vector quantity.

### Step 3: Analyze the third option - Charge of gold leaf experiment
- **Explanation**: Charge is a property of matter that causes it to experience a force in an electromagnetic field. Charge itself is a scalar quantity, as it does not have a direction associated with it.
- **Conclusion**: Charge is not a vector quantity.

### Step 4: Analyze the fourth option - Moment of a spinning body
- **Explanation**: The moment of a spinning body (often referred to as torque) is given by the cross product of the position vector (r) and the force vector (F). Since torque has both magnitude and direction (it can be clockwise or anticlockwise), it is classified as a vector quantity.
- **Conclusion**: The moment of a spinning body is a vector quantity.

### Final Answer:
The only vector quantity among the given options is the **moment of a spinning body**.

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