electricity Flashcards
which is positive and which is negative; cathode and anode?
cathode - negative
anode - positive
what is electro magnetic induction
a change in magnetic field induces an emf that induces current
how is magnetic flux measured
weber
what is fardays law of Electromagnetic induction
magnitude of induced emf is proportional to the rate of change of flux or E <× Ø1 - Ø 2 / t
what is a magnetic field
region where an attractive repulsive force is felt
in what direction do magnetic force lines point
north to south
what is an electromagnet
current carrying conductor
what is a solenoid
a coil whose length is linger than its radius
how do you make a solenoid stronger
place a magnetic core in it
what direction is a magnetic north pole
anti clockwise
what direction is a magnetic south pole
clockwise
what will a current carrying conductor experience in a magnetic field
a force perpendicular to current flow and perpendicular to magnetic field
what is conventional current direction
postive to negative
what happens if a current carrying wire enters a magnetic field parallel to magnetic flow direction
no force acts on it
what happens if a current carrying coil is placed in a magnetic field
it turns
what is a characteristic of a thermistor
resistence will drop dramatically at a certain temperature
what are the two main types of capacitors
an electrilytic capacitor and a parallel plate capacitor
what does dielectric mean
non conductive
what are 3 factors affecting capacitance in a parallel plate capacitor
distance between plates, permitivity of dielectric material, area of overlap
what is lenzs law?
the direction of current caused by electromagnetic induction will be opposite to the direction of the force causing it
how do you demonstrate faradays law?
what is the purpose of a transformer
to increase or decrease alternating voltage
what is the principle operation of a transformer
- the input voltage (Vin) in the first (or primary) coil creates an alternating current there, which then creates a changing magnetic field in the core.
- The secondary coil is inside this changing magnetic field and so it creates an emf in the secondary coil (Vout)
The voltage can either be increased (a step-up transformer) or reduced (stepped down). - This is controlled by the relative number of turns in the primary (Np) and the secondary (Ns).
what is alternating current
current that reverses direction over a set period of time
describe an experiment to show how resistance of an LDR varies with incident light
connect LDR to ohmeter, shine light with verying distances and observe change in resistance on ohmeter
what is rectification
conversion of a.c. ro d.c
what semiconductor is used for rectofication
diode
why is high voltage used to transport electicity efficiently
according to joules law, a) heat generated in wires is proportional to the square of current so b) a low current is needed to reduce heat thus c) a high voltage is used
list 4 sources of emf
dry cell, primary cell, secondary cell, mains
what is a semi conductor
a MATERIAL with varying resistance
what are two common semi conductors
silicon and gerarnium
what is valence
amount electrons in an atoms outer shell needed to fill the shell
what happens to a semi conductor like silicon when it heats up
a POSITIVE HOLE is left after an electron leaves
what is intrinsic conduction
conductivity in a pure semicondunctor material due to factors like HEAT or LIGHT
what is doping in semiconductors
adding impurities to increase extrinsic conductivity
what is a p-n diode
when P TYPE and N TYPE semiconductor materials are joined to allow CURRENT to flow in ONE DIRECTION
what is the depletion layer in a P-N DIODE
a neutral region where the electron holes and electons have filled each other and there no CHARGE CARRIERS
what is required for a P-N DIODE to work
for voltage to exceed JUNCTION VOLTAGE that exists in DEPLETION LAYER AND to be connected in FORWARD BIAS
what is forward bias
when the POSITIVE TERMINAL is connected to the p-type and the NEGATIVE TERMINAL is connected to n-type
what happens if a semicondictor is connected in reverse bias
depletion layer widens, current doesnt flow except for current leakage, diode eventually breaks
what unit is current measured in a) forward biased diode and b) reverse biased diode
a) milli amps and b) micro ampls
example of material added to a) p-type dope silicone and b) n-type dope silicone
a) boron b) phosphorus
