Chris: It's not often that you can impress your friends with your knowledge of physics, but when the Northern lights appear everyone wants to know how they are formed.
Emma: That's alright for those living in Norway!
Key Concepts
The equation for the force (in N) on a moving charge can be derived by considering the moving charges in a wire:
\(F=Bqv\)
Since the force is always perpendicular to the velocity, the resulting motion is circular.
Use quizzes to practise application of theory.
START QUIZ!
An electron moves at 400ms-1 in a perpendicular magnetic field of flux density 10 mT.
The magnitude of the force it experiences is:
F = Bqv = 10 x 10 -3 x 1.6 x 10 -19 x 400
An electron passes into a region of uniform magnetic field.
Which track shows the possible path of the particle.
The force will be initially down then always perpendicular to the motion.
Two particles are projected into a perpendicular magnetic field. The particles have the same charge and velocity but particle A has twice the mass of particle B. Each particle travels in a circular path.
The ratio radius of path A / radius path B
The radius is proportional to mass so particle A will have a path of 2 x radius of B
The diagram shows the path of a charged particle in a perpendicular magnetic field-
Which of the following statements gives a possible scenario?
As the particle loses KE its velocity gets less so the radius of circle is reduced. A + particle travelling from A to B has the correct force direction
A particle of mass m and velocity v travels in a circular path of radius r in a magnetic field of flux density B.
The radius of the path is given by the equation
centripetal force = magnetic force
mv2/r = Bqv
The particles that form the aurora:
more of a spiraling helix but spiraling is the best answer.
The unit of flux density is the Tesla.
An alternative unit could be:
F = Bqv
B = F/qv =N/Cms-1
The diagram represents an electron travelling into a magnetic field.
Which of the following represents a possible path
As the field gets weaker the radius gets larger so the electron takes longer to complete each circle.
The Aurora Borealis is only seen in the winter because
If you live in Norway you will know that the nights are not dark in the summer.
Add another component to the motion and you get a helix.How much of Moving charges in a magnetic field have you understood?
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