3. Electricity Flashcards
Protons and neutrons are examples of what
Nucleons
Absolute charge of electron in coulombs is
-1.6x10^-19C
How many electrons are in 1C
6.25x10^18 electrons
Relative mass of electrons
1/2000
If you have a 9v battery every coulomb of charge gets how much energy
9 joules
Potential difference is what
Energy that has been transferred by each coulomb of charge
Potential difference formula
V=E/Q. E is energy and q is charge
PD of 1v means each coulomb transfers how much
1J
Resistor networks
Groups of resistors to make an equivalent resistance
Resistance total formula in parallel
R total=R1+R2+R3
E.g. 1/R1+1/R2+1/R3
Then find reciprocal
Charge
A physical property of matter that causes it to experience a force when placed in and EM field
Current
Rate of flow of charged particles, defined by charge per unit time
Potential difference
Difference in energy stored per unit charge between two points
Resistance
An object property that opposes flow of charge
Work done
Energy transferred as matter is moved a distance against a force
Avagrado constant
6.02x10^-23
Emf
Electromotive force
Current equation
I=change in charge/change in time
Electromotive force
Supply / component which is putting electrical energy into a circuit.
Correct term of voltage
EMF
Voltage
Amount of energy a component transfers per unit
Voltage equation/emf/pd
Voltage =energy transferred / charge passing
Electron volt
Unit of energy that is generally used with sub atomic particles comes from equation V=E/Q
Current in series circuit
Same current all the way through
Current in parallel circuit
Splits across circuit
Voltages in series
Splits and adds up back to supply
Voltage in parallel
Identical voltage across branches
Resistance equation in series
Rtotal=R1+R2+R3
Ohmic conductor
Component through which the current is proportional to the voltage it is
Material property (resistivity,brittleness ,tensile strength and hardness)
Doesn’t depend on dimensions only what it’s made of
Object property (resistance ,breaking force )
Depends on the materials as well as dimensions and constructions
Difference between resistance and resistivity
Resistance depends on amount of something and resistivity depends on composition
What affects resistance in objects
Area-narrow means less space to flow
Length-long means will be harder to get through
Type of material (resistivity)
Resistance equation
R=pL/A
Resistance =resistivity x length/area
Resistivity
Materials ability to resist flow of charge. Materials of low resistivity are chosen for conducting circuits (gold etc)
Drift velocity is always _______than electron speed
Slower
Transportation equation
I=NAvQ
N-electron density
A-cross section area
V-drift velocity
Q-charge of electrons
Semiconductors got what
Lower electron density meaning few electrons are free to drift
Conduction bands
Allow charge to flow across the structure when a potential difference is applied.
Structure of semiconductor
Single atoms have electrons orbiting in shells.
Adding energy will increase the level the electrons can reach then ionising the atom when the electron is free to leave.
Atoms combine to form giant lattice the energy levels act in different way
Some energy levels are still possessive to the atom.
Ohms law
Current through conductor is directly proportional to PD across it( if temperature and external environment remain the same)
Non ohmic conductor
Current through component affects its own temperature
What is the tool used to measure diameter of a wire
Micrometer
What is drift velocity
Slow overall moment of electrons
A slight decrease in N for metals at higher temperatures is due to what
Thermal expansion
Semiconductors
Generally solid materials that only have small numbers of delocalised electrons that are free to conduct
E.g silicon
How are energy bands formed
Whether there are many atoms close together, they allowed energy levels become much wider, forming energy bands
Valence band every level
Electrons of this amount of energy remain highly to atoms and do not form part of any electric. Current, those are gain energy to jump up to the conduction band they can delocalised and can move through the part of a current. 
Number of delocalised electrons in a semiconductor is____than metals for the same applied voltage.
Lower
What happens when an electron enters a conduction band and moves away
Leaves the atom with an effective positive charge
An insulator has what type of bands
Empty, conduction band and full valance band
A semiconductor has what type of bands
Almost empty, conduction bands and almost full valance band 
A metal has what type of bands 
Almost full conduction band and valance band 
The empty space electron has left is referred to as what 
Positive hole 
What is known for a few charge carriers can pass at low voltages 
Leakage current 
What are insulators? 
Materials in which the energy gap between the valance band and the conduction band is so large, there are virtually zero electrons available for conduction 
Resistance increases with high temperatures how
The higher level of internal energy in the material causes more vibration of the fixed irons, and these collide more often the charge carriers to reduce their speed of movement through the material. Reduce the temperature therefore reduce resistance, allowing greater current flow. 
Below a certain critical temperature, what happens to the resistance?
Resistance suddenly drops to 0, this is called superconductivity 
What is superconductivity?
Resistance drops to 0, because it reaches a critical temperature 
Difference between PD and EMF
PD is electrical energy transferred between two points , or the electrical energy transformed or converted to other forms
EMF is the energy supplied to a circuit
Kirchhoff rule 1
Total current entering a junction is equal to total current leaving it
Current is conserved
Kirchhoff law 2
In any closed loop network the total emf is equal to the sum of p.d drops
Potential divider equations with V
V1/R1 =v2/R2
V1/v2=R1/R2
Potential divider equation
V out=v in x R2/R1 +R2
Potentiometer
Version of the potential dividing which is single resistance. Wire is used in two parts to form material resistances a sliding connection on the wire can be adjusted to alter the comparative resistances as fast out of output PD from the potential meter.
NTC
Negative temperature coefficient
Potential divider in sensor circuit
Lamp is in parallel with LDR, so will be powered by the same voltage as that across the LDR
Potential divider
Circuit designed to provide specific voltage values by splitting an EMF across two resistors
Internal resistance
Resistance of an emf source
Internal resistance on graph
Negative gradient slope
EMF on graph
Y intercept
Effect of having an internal resistance
EMF will never be able to fully supply it’s notional maximum voltage They always be a small drop in voltage over the entire resistance, and this drop will be bigger with a higher current. 
Power
Rate of transfer of energy or rate of doing work
Expression for Current in terms of emf
I=emf I(R+r)
What happens to the PD across the thermistor as temperature increases?
As temperature increases number of free charge characters and faster increase so resistance decreases faster resistance as a proportion of total resistance decreases PD across thermistor decreases
Using an ammeter with non-resistance but is affected by using for me with a lower resistance. Explain why 
Ammeter
If family has resistance currently decreased, but doesn’t affect the determination because current through cell is measured
Or doesn’t affect whether the determination because of a measure is the terminal PD for that current?
Voltmeter
Vote me has smaller resistance. It would draw current measured current not current through cell
