The correct option for the direction of the magnetic force experienced by a straight current-carrying conductor placed in a uniform magnetic field is: **B. Perpendicular to both the current direction and the magnetic field direction.** ### Detailed Explanation To understand why option B is correct, we need to delve into the principles of electromagnetism, specifically the interaction between electric currents and magnetic fields. 1. **Understanding the Right-Hand Rule**: - The right-hand rule is a mnemonic used to determine the direction of the magnetic force on a current-carrying conductor in a magnetic field. - To apply the right-hand rule, follow these steps: - Extend your right hand. - Point your thumb in the direction of the conventional current (the flow of positive charge). - Point your fingers in the direction of the magnetic field lines (from north to south). - Your palm will then face in the direction of the magnetic force acting on the conductor. 2. **Magnetic Force on a Current-Carrying Conductor**: - When a conductor carrying an electric current is placed in a magnetic field, it experiences a magnetic force. This force is given by the formula: \[ F = I \cdot L \cdot B \cdot \sin(\theta) \] where: - \( F \) is the magnetic force, - \( I \) is the current in the conductor, - \( L \) is the length of the conductor in the magnetic field, - \( B \) is the magnetic field strength, - \( \theta \) is the angle between the direction of the current and the magnetic field. - For the maximum force, \( \theta \) should be 90 degrees (i.e., the current and magnetic field are perpendicular), which simplifies the equation to: \[ F = I \cdot L \cdot B \] 3. **Direction of the Force**: - The force is always perpendicular to both the direction of the current and the direction of the magnetic field. This is a fundamental characteristic of the interaction between magnetic fields and electric currents. ### Why the Other Options Are Incorrect - **A. Parallel to the magnetic field direction**: - This option is incorrect because the magnetic force cannot be parallel to the magnetic field. The force is always perpendicular to the magnetic field lines, as established by the right-hand rule. - **C. In the same direction as the current**: - This option is also incorrect. The magnetic force does not act in the same direction as the current. Instead, it acts at a right angle to the current's direction, as indicated by the right-hand rule. - **D. Opposite to the direction of the magnetic field**: - This option is misleading. The magnetic force does not act opposite to the magnetic field direction. Instead, it is perpendicular to both the current and the magnetic field, which means it can be in any direction that is not aligned with either. ### Summary of Key Points - The magnetic force on a current-carrying conductor in a magnetic field is always **perpendicular** to both the current and the magnetic field. - Use the **right-hand rule** to determine the direction of the magnetic force: thumb (current), fingers (magnetic field), palm (force). - The formula for the magnetic force is \( F = I \cdot L \cdot B \cdot \sin(\theta) \), with maximum force occurring when the current and magnetic field are perpendicular. - Understanding the relationship between current, magnetic fields, and forces is crucial in electromagnetism and applications like electric motors and generators. This thorough understanding will help you tackle questions related to magnetic forces in future exams effectively!