Chp 20- Magnetism Flashcards
What does ferromagnetic mean?
show strong magnetic effects
what is magnetic declination?
angular difference between the direction of a compass needle (which points along the magnetic field lines) at any location and true (geographical) north
What happens when a compass needle is placed near a straight section of current-carrying wire?
A compass needle placed near a straight section of current-carrying wire expe- riences a force, causing the needle to align tangent to a circle around the wire,
Relate how magnetism works according to newton’s third law.
we should expect that a magnet exerts a force on a current-carrying wire.
What happens to the force on the wire when a current flows in a wire? (normal, reverse and general
force is directed at right angles to the magnetic field direction, downward.
If it is reversed the force is in the opposite direction, upward.
The direction of the force is always perpendicular to the direction of the current and also perpendicular to the direction of the magnetic field, B .
What is the general statement of what happens to a force on a wire when a current flows through it?
The direction of the force is always perpendicular to the direction of the current and also perpendicular to the direction of the magnetic field, B .
Describe the right hand rule
Orient your right hand until your outstretched fingers can point in the direction of the conventional current I, and when you bend your fingers they point in the direction of the magnetic field lines, B . Then your outstretched thumb willpointinthedirectionoftheforceFB onthewire.
What is the magnitude of the force directly proportional to?
magnitude of the force is directly proportional to the current I in the wire, to the magnetic field B (assumed uniform), to the length l of wire exposed to the magnetic field and the angle between the current direction and the magnetic field (proportional to sin)
F ∝ IlBsinu.
At what angle is the force strongest at?
90º
What angle is there no force at all?
0º
What is the Si unit for magnetic field B?
T (tesla)
What is the magnetic field of the Earth at its surface?
1 G or 0.5 * 10–4 T
What is the direction of the force perpendicular to?
The direction of the force is perpendicular to the magnetic field B and to the velocity vB of the particle.
What is the path of a charge particle moving a plane perpendicular to?
The path of a charged particle moving in a plane perpendicular to a uniform magnetic field is a circle
An electric charge q moving in an electric field EB can be decelerated to a stop if the force FB = qEB (Eq. 16–5) acts in the direction opposite to the charge’s velocity. Can a magnetic field be used to stop a charged particle?
No, because the force is always perpendicular to the velocity of the particle and thus can only change the direction but not the magnitude of its velocity. Also the magnetic force cannot do work on the particle (force and dis- placement are perpendicular, Eq. 6–1) and so cannot change the kinetic energy of the particle, Eq. 6–4.
