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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

Total Score:

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