A current-carrying wire is placed in a uniform magnetic field, but there is no magnetic force on it. How is this possible?
This situation is possible when the direction of the current in the wire is parallel or antiparallel to the direction of the magnetic field. According to the magnetic force equation, F = (I * L) * B * sin(θ), where F is the magnetic force, I is the current in the wire, L is the length of the wire, B is the magnetic field strength, and θ is the angle between the current direction and the magnetic field direction.
If the current direction is parallel or antiparallel to the magnetic field direction, sin(θ) becomes zero, and consequently, the magnetic force acting on the wire becomes zero. This means there will be no magnetic force on the wire, even though it is carrying a current.
To determine the direction of the current in the wire and the direction of the magnetic field, you can use the right-hand rule.
1. Place your right hand so that your thumb, index finger, and middle finger are all perpendicular to one another.
2. Point your index finger in the direction of the current in the wire.
3. Point your middle finger in the direction of the magnetic field.
4. Your thumb will then indicate the direction of the magnetic force acting on the wire.
If the thumb points in a direction parallel or antiparallel to the wire, it means there is no magnetic force on the wire. Otherwise, if the thumb points in a different direction, there will be a magnetic force acting on the wire.