Electricty Flashcards
What is Ohm’s Law?
For a metal conductor current is directly proportional to voltage so long as temperature is constant
Define current
Flow of charge
Define potential difference
Energy transferred from electrical to other forms per unit charge
Define emf
Energy available to be converted to electrical energy per unit charge
Define resistance
A property of a component that regulates electric current
=potential difference
—————————
current
Define mean drift velocity
Average displacement travelled of the electrons along the wire per second
Kirchhoff’s 1st Law:
The sum of the current entering a junction is equal to the sum of the current leaving a junction (charge is conserved)
Define resistivity
A measure of how strongly a material opposes the flow of electric current, ratio of the product of resistance and cross sectional area and its length
Define power
Rate of work done or energy transfer
Kirchhoff’s 2nd Law:
The algebraic sum of the emfs and the pds is equal to 0 (conservation of energy)
Define terminal pd
Energy transferred from electrical energy to other forms per unit charge
=emf-lost volts
Define internal resistance
The resistance that cause the lost volts
Define the electron volt
Energy an electron gains when its accelerated across a pd of 1 volt
Define an amp
1A is the same as 1 coulomb of charge passing a point in 1 second
Which way is conventional current?
From + to -
Which way is electron flow?
From - to +
Define a coulomb
1C is the charge that flows past a point in 1 sec when there is a current of 1A
Equation including drift velocity
I=nAve
Where I=current n=amount of charge carriers per cubic metre A=cross sectional area v=drift velocity e=charge value
What’s the difference between pd and emf
Both are energy transfer per unit charge it emf is from chemical to electrical and pd is from electrical to other forms
Define the volt
1 volt is the potential difference between 2 points when 1 joule of work is done to move 1 coulomb
Define an ohm
1 ohm is the resistance of a component that has a pd of 1 volt per ampere of current
Current=
Q
—
t
What causes a substance to either be a conductor, semi-conductor or insulator?
For conductors the electrons are very free to move around and so the value of n for the substance is high. For semi conductors the electrons are locked down until energy is put in to it, examples of these are thermistors and LDRs. For insulator n is very small and so there aren’t many free electrons at all to carry the charge to create a current
Equation for the energy transfer of charged particles
eV=0.5mv^2
Resistance=
Potential Difference
—————————
Current
As light intensity increases, the resistance of an LDR….
Decreases
As temperature increases the resistance of a thermistor….
Decreases
Power=
Potential difference x current
OR
current x current x resistance
OR
p.d x p.d
—————-
resistance
Define the kilowatt-hour
Energy transferred by a device working 1kW for 1 hour
Sum for the total resistance of resistors in series
R=R1+R2
Sum for the total resistance of resistors in series
1 1 1
— = — + —
R R1 R2
Equation including internal resistance
E=I(R+r)
E=V+Ir
E=emf V=potential difference I= current R=resistance in circuit r=internal resistance
What are circuits called when the pd is shared between the components?
Potential dividers
V(out)=
R1
——— x V(in)
R1+R2
