Electricity Flashcards
define p.d.
The energy transferred frome lectrical enmergy to other forms of energy per unit ccharge due to the charge doing work on the componenents
The change in potential energy per unit charge between two points, due to the charge doing work on circuit components
V = E/Q
define electromotive force (e.m.f.)
The change in electric potential energy per unit charge between two points, due to work being done on the charge, for example by a battery or a power supply
ε = W/Q where ε = electromotive force (in Volts), W = work done (in Joules) and Q = charge (in Coulombs)
what is true about the energy of a charged particle in a mas spectrometer
When a potential difference accelerates a charged particle, the energy transferred is equal to the kinetic energy gained by the particle (usually an electron).
define a volt
1 volt is the potential difference between two points when a 1 C charge passing between the points experiences a change in electric potential energy of 1 J
what is the charge and mass of an electron
charge: 1.6 x 10^-19 C
mass: 9.11 x 10^-31 kg
define resistance
R = V/I where R = resistance (in Ohms), V = potential difference across component (in Volts) and I = current in the component (in Amps).
Resistance is a measure of a componenets opposition to the flow of charge.
What is resistivity
A property of a material, measured in Ω m. ρ = RA/l where ρ = resistivity (in Ohm.metres (Ω⋅m)), R = resistance (in Ohms), A = area (in m2) and l = length of wire (in m).
A material has resistivity of 1 Ω m when a cubic metre of material has a resistance of 1 Ω
how does resistivity change with the dimentions of a wire
it doesn’t Resistivity is a property ofa material (at contant temp)
it can only change with temperature
Why does resistance increase with temperature
the particles ofa substance vibrate more, so the free elections are impeded in their movementby the particles hence the resistance increases with temperature
what is the charge of one electron and how can we use this value
1.6*10^-19C
aue can use this value to calculate how many electrons flow pasta point by dividing the charge passing that point by this constant
whatis emf
the energy transferred from chemical to electrical energy per unit coulomb due to the components doing work on the charge
state kirchhoffs first law
all charge entering a junction is the same as all the charge exiting a junction at the same time
state kirchhoffs second law
the sum of emfs is equal to the sum of pds around a closed loop
describe the current & voltage in a series circuit
the current is the same in all components
the p.d. is shared amongst components
describe the current and voltage in a parallel circuit
the sum of pds in each branch is equal to the emf
the current splits at every junction
what is mean drift velocity
the average velocity attained by charged particles, such as electrons, in a material due to an electric field, resulting in a net flow of charge
whatis number density
the number of delocalised electrons per meter cubed of a substance
What is the equation for MDV
I= Anev
what direction does conventional current flow
positive to negative
define resistivity
a property of a material which describes the extent to which a material opposed the flow of current
equation for resistivity
resistivity x length = cross sectional area x resistance
how does length affect the resistivivity of a material
it doesnt
what are the equations fro power
P = I^2R
P = IV
P = V^2/R
P = E/t
what does a NTC thermistor do
the resistance decreases as the temperature increases (this isnt typical of a resistor)
describe the IV characteriscs in an ohmic resistor
the voltage is directly proportional to the current
the resistance is constant provided that the temperature is the same
describe the IV characteristics of a diode
what is the threshold pd
a diode only lets p.d flow in one direction, until it teaches the threshold p.d, 0.7V, when it increases and becomes an ohmic resistor
what is the rule for resistance in a parallel circuit
1/R1 + 1/R2 + 1/R3 = 1/Rt
the total resistance will be less than the resistance of the smallest resistance
note that R1, R2, R3 are not individual resistances, but the resistances of different branches in parallel
how does resistance change in a LDR
as light intensity increases, the resistance decreases
define power
the rate of energy transfer
define work done
energy transfer
how does an electron gun work
the negative termical is connected to a fillament which becoimes charged with a huge p.d.
due to the p.d. the fillament undergoes thermionic emmoisson and recveases electrons
which are attracted to the anode (the pos terminal connected to some metal) witrh a hole in it which focuses the electrons into a beam
define terminal voltage
The terminal voltage is the potential difference between the terminals of a power source when the power source is connected by a complete circuit to a load (an external resistance)
define internal resistance
Resistance due to opposition of flow of charge within a source of e.m.f.
ε = I(R+r) where ε = e.m.f. (in Volts), I = current (in Amps), R = load resistance (in Ohms) and r = internal resistance (in Ohms)
define lost volts
The difference between the terminal voltage and the e.m.f. of a source of e.m.f due to energy being dissipated across the internal resistance of the power source
define terminal p.d.
The potential difference measured across the battery/power supply when that battery/power supply is connected by a complete circuit to a load (external) resistance. If there is no internal resistance, the terminal p.d. will equal to the e.m.f.
define a potential divider
A circuit which allows a user to vary an output potential difference using the principle of shared potential differences given by Kirchhoff’s Second Law
