P2 Flashcards
which equation links charge flow, current and time?
charge flow = current x time
which equation links p.d., current and resistance?
p.d. = current x resistance (IVR on triangle)
which equation links power, energy transferred and time?
power = energy transferred / time
which equation links energy transferred, charge and p.d.?
energy transferred = charge x p.d.
which equation links power, p.d. and current?
power = p.d. x current
which equation links power, current and resistance?
power = current² x resistance
describe the live wire
brown
provides alternating p.d. at about 230V
from mains supply
describe the neutral wire
blue
completes circuit
carries away current
0V
how does electricity flow through the wires?
in through live wire
out through neutral wire
describe the earth wire
green and yellow protects wiring, for safety stops appliance casing from becoming live only carries current if there's a fault 0V
what’s electric current?
the flow of electrical charge
size of the electric current is the rate of flow of electrical charge
what conditions are needed for electrical charge to flow?
closed circuit
source of p.d.
unit for current?
ampere/amps (A)
unit for charge?
coulombs (C)
unit for time?
seconds (s)
definition of p.d.
driving force that pushes charge around (the circuit)
definition of resistance
anything that slows down the flow
definition of resistance
anything that slows down the flow (current)
state the relationship between resistance and current
the greater the resistance across a component, the smaller the current that flows
for a given p.d. across the component
state the relationship between current and charge
more charge passes around a circuit when a larger current flows
what does the ammeter do?
measures current
always placed in SERIES with whatever is being measured
what does the voltmeter do?
measures p.d.
always placed in PARALLEL to whatever is being measured
what’s an ohmic conductor?
at a constant temp.
current flowing though it is directly proportional to the p.d. across it
(resistance stays constant as current changes)
what happens to the R value for some resistors?
for some the R value stays constant
for others it can change as the current changes
what’s an example of an ohmic conductor?
a resistor at a constant temp.
for which components and resistors does the resistance not stay constant?
filament lamps
diodes
thermistors
LDRs
what’s the relationship between current and resistance in non-ohmic conductors?
resistance changes with current through the component
describe the trend in a filament lamp
when an electrical charge flows through, energy is transferred to the thermal energy store of the filament which is designed to heat up
resistance increases as the temp. of the filament increases
as current increases filament heats up more and resistance increases
less current can flow per unit p.d. so graph curves/gets shallower
describe the trend in a diode
current only flows in one direction
if current is reversed there’s very high resistance
describe the trend in an ohmic conductor
at a constant temp.
current is directly proportional to p.d.
so the graph has a straight line through the origin
define the term ‘I-V Characteristics’
refers to a graph that shows how the current flowing through a component changes as the p.d. across it increases
what’s a linear component?
have an I-V Characteristic that’s a straight line
give an example of a linear component
fixed resistor
what’s a non-linear component?
have curved a I-V Characteristic that’s curved
give some examples of a non-linear component
filament lamp
diode
