MCQs: Charges in a B field
The Northern Lights only occur in the North (and the Sourthern Lights in the South) because:
The Earth's magnetic field acts like a magnetic bottle trapping the charged particles coming from the sun; they spiral back and forth along the field lines only getting close to the atmosphere at the poles.
The diagram shows the path of two particles travelling into a B field with equal velocity.
Paths have same radius so their masses are equal. The forces act in opposite directions so the charges must be opposite.
B is positive and A is negative.
The diagram below represents a charge moving into a magnetic field.
On entering the field, the direction of the force on the charge is:
Because the charge is negative, the current is opposite to charge movement. Use Fleming's left hand rule..
The diagram below represents a charge moving into a magnetic field.
On entering the field, the direction of the force on the charge is:
Current is in the same direction as this positive charge. Use Fleming's left hand rule.
The diagram below represents a conductor in a magnetic field.
If the force experienced by the conductor is 1 mN, it's resistance is:
F = BIL
I =V/R so F = BVL/R
R = BVL/F = 0.05 x 6 x 0.03/1x10-3 = 9 Ω
The diagram below represents the magnetic field lines at the surface of the Earth.
The vertical component of the magnetic field is:
The vertical component is not next to the angle. Use trigonometry.
The diagram below represents a conductor in a magnetic field.
If the flux density is 10 mT, the force on the conductor is:
F = BIL = 10 x 10-3 x 5 x 0.04 = 0.002
The diagram below represents a conductor in a magnetic field with the current going into the page.
The direction of the force is:
Use Fleming's left hand rule
A current-carrying conductor is placed inside the solenoid as shown.
The force acting on the conductor is:
Current is parallel with field (so there is no perpendicular component).
The diagram represents a current-carrying conductor in a magnetic field.
The direction of the force experienced by the conductor is:
Use Fleming's Left hand rule