A-LEVEL PHYSICS: YT video: All of AQA Electricity Explained (PhysicsOnlineYOUTUBE) Flashcards
3 basic quantities we are interested in in a-level: (3)
V I R
current:
rate of flow of charge
I = …
I=ΔQ/Δt
basic charge carriers in circuit:
e-
conventional current:
current that flows + to -
despite conventional current, the charge carriers themselves (e-) are actually…
moving - to + terminal
conventional current goes ___ to ___, but the charge carriers (e-) go ___ to ___
+ -, - +
what causes current to arise in the first place in a circuit?
difference in potential between terminals (+ & -)
V = …
V=E/Q
potential difference:
energy transferred per unit charge
in ohmic conductors, I & V are…
directly proportional
resistance:
the ratio of the potential difference across a component divided by the current in that component
R = …
R=V/I
ammeter goes in ___, voltmeter goes in ___
series, parallel
ammeter measures…
current in series component
voltmeter measures…
potential difference between 2 points in a circuit across a component (parallel)
I-V graphs for ohmic conductors:
straight line through the origin (directly proportional)
filament lamps are…
non-ohmic conductors
diodes enable:
current to flow in only one direction
if you want to measure the resistance of a piece of wire, it depends on the…
why?
length
bc when longer, there’s more obstacles that the e- may collide with
if you have a piece of wire twice as long, it will have…
twice the resistance
why does the resistance of wire depend on length?
bc when longer, there’s more obstacles that the e- may collide with
if we had a thicker wire (bigger ___), there’s more pathways for the ___ ___ (___) to move
C-S.A., charge carriers, e-
resistivity equation:
R=ρ L/A
resistivty:
resistivity is an intrinsic property of a material, resistance of a conductor of unit C-S.A. & unit length
resistivity, just like resistance, depends upon…
temperature
as temperature increases, resistance…
increases
why does resistance increase when temperature increases? (3)
-as conductor gets hotter, the +ve metal ions vibrate more
-makes it more difficult for the free e- charge carriers to flow through the lattice
- e- collide more with +ve metal ions, increasing vibrations & temperature
explain temperature increase for semiconductors: (3)
-semiconductors: e- charge carriers bonded to material
-when temp. increases, there’s enough energy for the e- to move out of the material
-increasing current
Thermistor:
thermal resistor: when temperature increases, resistance decreases
negative temperature coefficient thermistor:
as temperature increases, resistance decreases
what happens as a semiconductor gets cooler? (3)
-the semiconductor particles vibrate less & less
-gets to a point where resistance suddenly drops to 0Ω
-superconductivity (happens at the critical temperature)
in circuits, ___ & ___ are conserved
charge, energy
since Q is conserved in circuits, Current in to a junction = …
Current out of the junction
(ΣI in = ΣI out)
Kirchoff’s first law:
ΣI in = ΣI out
Σε = …
ΣV
2 main types of circuit:
series, parallel
in a series circuit, current is…
the same everywhere
ε (series) = …
ε = V1 + V2 + V3 …
ε (parallel) = …
ε = V1 = V2 = V3 …
Rtotal (series) = …
Rtotal = R1 + R2 + R3 …
Rtotal (parallel) = …
Rtotal = 1/R1 + 1/R2 + 1/R3 …
power equations (P=) …
P=IV
P=I^2 R
P=V^2 / R
P=ΔE/Δt
potential dividers consist of:
power source, 2 resistors
ε = …
ε = IR + Ir
