Chapter 15 Flashcards
What does the right hand rule describe?
The direction of a magnetic field around a current-carrying wire.
What happens if you put a current-carrying wire into an external magnetic field?
Field around the wire and field from the magnets interact causing the field lines from the magnet to contract and form a “stretched catapult” effect.
Equation for the size of the force on a current-carrying wire
F = BIL
Equation for permeance
ϕ = ΛNI
Flux is maximized by:
- Large area of cross section
- Small air gaps
- Large N and I
Equation for permeance and permeability
Λ = μA/L
What do flux lines tend to do?
Tend to contract.
What is magnetic field strength/flux density?
Measures the strength of the magnet per unit area.
What can flux be thought of as?
Total number of field lines.
What happens when a conducting rod moves through a magnetic field?
Its electrons will experience a force meaning that they will accumulate at one end of the rod, thus inducing an emf across the rods as a battery would.
If this rod is part of a complete circuit, then a current is induced.
When is e.m.f induced?
Whenever there is relative motion between a conductor and a magnet.
Whenever flux lines are cut.
Under what condition will an induced emf also induce a current?
If the circuit is complete.
What does Lenz’s Law state?
The induced e.m.f is always in such a direction as to oppose the change that caused it.
What is the force on a moving charge?
F = qvB (sin 0)
In what way can the coils of a transformer be altered to increase efficiency?
Conductance of the copper coils need to be high to limit energy loss.
What is an ideal transformer?
One in which all the electrical energy put into one coil comes out of the other coil
What are eddy currents?
Eddy currents are currents that are induced in a conductor due to a changing magnetic field.
How can we limit the inefficiency caused by eddy currents in the core?
Laminating the core with layers of iron separated by thin layers of insulators will reduce the amplitude of the eddy currents as currents cannot flow through the layers of insulator.
What is done to limit the effects of heat produced by resistance in the copper wires?
Thick copper wires used which have low resistance.
