Electricity NAB Flashcards
Force on a conductor in a magnetic field. Magnitude and direction
F=BILsin0
Right hand rule!
Right Hand Rule?
First - magnetic FIeld
Second - electric current
Thumb- thrust
Definition of a tesla
Use the formula for F in mag field.
Rearrange for B. Find that a magnetic field of one tesla creates a force of one Newton on a conductor of one metre with a current of one amp.
Motion of a charge in mag field derivation
F= B I L sin0
F= B (Q/t) (vt) sin0
F= BQV
Radius of Orbit of charge in mag field
R= MV/ QV
Describe A crossed field
A crossed field with parallel plates creating E field and magnets creating mag field. They must be perpendicular to each other, making the resultant forces on a charge passing between them have opposite direction.
Derive expression for speed of an electron moving straight through a crossed field
Fb=Fe
Bqv=Eq
V=E/B
Derivation of charge to mass ratio
Use v=E/B
Start with Fe=Fb
Equate to mv^2 / r
Rearrange for q over m
Substitute v = E/B to get rid of velocity
Bingo
Q/m = E/(B^2 * R)
Why doesn’t current reach it’s maximum value immediately??
The increasing current creates a changing magnetic field around the inductor. An emf is induced in the conductor and it opposes the build up of current. The back emf decreases as the rate of increase of current reduces an the current approaches it’s maximum value as the back me reduces to zero.
formula for self induced back emf
3 = - L * dI/dt
L is the inductance. In Henry units
BUT 3 is in volts!!!
Back emf at instant circuit is closed??
Equal, but opposite, to battery emf
Strong force
Hold the protons and neutrons together in the nucleus of an atom. Overcomes repulsion between positive protons.
Short range.
Strongest force. Think of the energy inside an atom!! E=mc^2
Weak force
Radioactive decay.
Neutron decays into proton and electron. Weak force overcomes attraction and ejects beta particle (electron that doesn’t orbit) from nucleus
