Electricity Flashcards
What is current?
-The rate of flow of charge
-Measured using an ammeter in series
What is charge?
-One Coulomb is the amount of charge which passes in 1 second when the current is one ampere
What is potential difference?
-To make electric charge flow, you need to do work on it
-Voltage is defined as the work done per unit charge moved
-The P.D is one volt when 1 joule of work moves 1 column of charge through the component
-Measured using a voltmeter in parallel
What is full scale deflection?
-The maximum value to an ammeter or a voltmeter
What is a charge carrier?
-A current is the rate of flow of charged particles, called charge carriers
-Are free electrons sometimes known as conduction electrons
-A flow of positive particles produces the same current as the equal flow of negative particles
What is an insulator?
-Ionic crystals are insulators, but once molten, can conduct, with the positive and negative ions as the charge carriers
-Gases are insulators, but if you apply a high enough voltage electrons get ripped out of atoms, giving you ions or a spark
What is the mean drift velocity?
-When current flows, the electrons move randomly in all directions, but drift one way overall
-The mean drift velocity is the average velocity but is much smaller than the actual speed
What is the charge on an electron?
-1.6 x10^-19
How can charge carriers change?
-In a metal, the charge carriers are free electrons, or the ones in the outer shell
-There are loads of charge carriers per unit volume, so the drift velocity is small
-Semiconductors have fewer charge carrier, so the drift velocity has to be higher
-A real insulator have very minimal charger carriers, or 0 so there will be low or no current
What is resistance?
-How much current for a particular potential difference depends on the resistance of the component
-How difficult it is to get current to flow
-Controlled using a resistor
-A component has one 1ohm is a potential different of 1V makes a current of 1A flow through it
What controls a wire’s resistance?
-Length: The longer the wire, the more difficult it is to make a current flow
-Area: The wider the wire, the easier it is for current to flow
-Resistivity: Depends on the material the wire’s made from, or depends on the environment
-Is typically very small, and depends on the number density of charge carries, and the men
What is an ohmic conductor?
-Have to obey Ohm’s law, when the temperature is constant, the current through is directly proportional to its potential difference
-This means the resistance is constant
How does temperature affect resistivity?
-Charge is carried through metals by free electrons in a lattice of positive ions
-Heating up a metal makes it harder for electrons to move about, the lattice of ions vibrates more when heated, meaning the electrons collide with them more frequently
-When kinetic energy is lot, their speed and their mean mean drift velocity decreases, so current decreases and resistance increases
What is a semiconductor?
-Have a higher resistivity than metals as there are fewer charge carriers
-If energy is supplied to some types of semiconductors, more charge carriers are released, so the current increases
-This means they can make sensors for detecting changes their environment, like thermistors, LDRs and diodes
What is electrical power?
-The rate of transfer of energy
