5.4 Magnetic Fields Flashcards
What will an electric curet in a wire produce?
A magnetic field - a vector whose direction is tangent to the magnetic field lines.
What is magnetic force?
A magnetic field B exerts a force on moving charges F=qvBsin@ and electric currents F=BILsin@.
How will a charged particle of mass m and charge q that enter a region of magnetic field B at right angles to the magnetic field?
It will move in a circular path of radius R given by: m(v^2/R) = qvB —> R = mv/qB
Why does the magnetic force do no work on the charged particle?
Because the force is at right angles to its velocity. Therefore the magnetic force cannot change the speed of the particle only the direction of the velocity.
Why will parallel wires carrying current attract or repel each other?
Because each wire produces magnetic fields at the position of the other wire and so a magnetic force is exerted. Parallel currents attract and antiparallel curet repel. The forces on equal lengths of wire are equal and opposite even if the current are different.
What is the ampere?
Two parallel conductors 1m apart have a current of 1A in them if the force on 1m of their length is exactly 2x10^-7N
What happens when an electron enters a region of electric and magnetic fields?
An electron is negatively charged so the electric force on it is opposite in directions to the electric field. The right hand rule gives a downwards direction for the magnetic force on the electron.
What is important about an electron in magnetic and electric fields being undeflected?
The upwards electric force on the electron has been cancelled by the downwards magnetic force so qE=qvB thus E=vB.
What happens if a positively charged particle enters the electric and magnetic fields?
It would be undeflected if it entered at the same velocity.
