Chapter 23 - Magnetic Fields Flashcards
What causes a magnetic field?
Moving charges or permanent magnets.
Fleming’s Left Hand Rule
Thumb: motion of wire.
First finger: direction of magnetic field
Second finger: direction of conventional current.
What does θ mean in the F = BILsinθ formula?
Angle between the field and the current.
Define 1 Tesla.
When a wire with 1 A is placed perpendicular to a magnetic field and experiences 1 N per m of length.
Equation for force on charged particle travelling at right angles to a uniform magnetic field.
F = BQv
Why does a charged particle have a circular path in a uniform magnetic field?
F is always perpendicular to the velocity.
What do velocity selectors do?
Uses electric and magnetic fields to select charged particles of specific velocity (fields cancel out and they can leave through slit).
Faraday’s law of electromagnetic induction.
Induced e.m.f is directly proportional to rate of change of magnetic flux linkage.
Lenz’s law.
Direction of induced e.m.f. is always such as to oppose the change producing (conservation of energy).
What does the θ in the equations for magnetic flux/linkage represent?
Angle to the normal.
Maximum induced e.m.f is directly proportional to…
B, A, N, frequency of rotating coil.
How do transformers work?
AC supplied to primary coil, resulting in alternating magnetic flux.
Iron core contains magnetic field.
Secondary coil linked by an alternating magnetic flux linkage.
How can you improve the efficiency of a transformer?
Low resistance windings - reduce power loss due to heating effect.
Laminated core with layers of irons separated by insulator prevents eddy currents.
Soft iron core is easy to magnetise/demagnetise.
