unit 1.5 - electric circuits REMASTERED Flashcards
describe current
flow of electrons around a circuit
describe voltage
the ‘driving force’ that pushes the current around the circuit
describe resistance
anything in the circuit that opposes/ slows down the flow of current
increasing the voltage will _____ the current flow
increase
increasing the resistance will _____ the current flow
decrease
the ammeter measures current ________ a component and must be placed in ______ with the component
through
series
the voltmeter measures voltage ________ a component and must be placed in ______ with the component
across
parallel
another word for voltage is
potential difference (pd)
in a series circuit
the total resistance is equal to…
…the sum of all resistances
in a series circuit
the same _____ flows through all parts of the circuit
current
in a series circuit
the supplied voltage is equal to…
…the total voltage across all components
in a series circuit
the bigger the resistance of a component…
…the bigger its share of the supply voltage
in a parallel circuit
the _______ is the same across all components
voltage
in a parallel circuit
the total current around the circuit is equal to…
…the sum of all currents flowing through the branches
in a parallel circuit
the lower the resistance of a component…
…the higher the current through it
in a parallel circuit
the current either ___ or _____ where branches meet. The total current going in to a junction must equal…
splits , rejoins
…the total current leaving it
in a parallel circuit
the total resistance of the circuit is always less than…
…the lowest branch resistance
The [longer/shorter] the wire, the greater the resistance
longer, more atoms for electrons to collide with, slowing down current
the [thicker/thinner] the wire, the smaller the resistance (width)
thicker, more paths for electrons between atoms, increasing current
the [hotter/colder] the wire, the greater the resistance (temperature)
hotter, hotter atoms vibrate more causing more collisions with electrons
How to calculate total resistance in series
R = R1 +R2 + R3 + …
How to calculate total resistance in parallel
R = 1/R1 + 1/R2 + 1/R3 + …
What is Ohm’s law
‘The voltage across a metal conductor is proportional to the current through it, provided the temperature stays constant’
how are V, I and R related? (not equation)
The large the resistance, the greater the voltage needed to push current through
Voltage equation
V = I x R
show an example of a standard test circuit
———–|l—————
l l
l [/]
l l
—–x————A———
l–V–l
x - component
A - Ammeter
[/] - variable resistor
|l - battery
V - voltmeter
VI graph about resistor shows?
Does it obey Ohm’s law?
a) The current through a resistor is proportional to voltage (temps constant) / Ohms law
b) Yes
VI Graph for resistor
how does current vary as voltage increases?
current is proportional to voltage (if temp is constant)
VI Graph for wire
how does current vary as voltage increases?
Different graph gradients, but all obey ohm’s law (if temp is constant)
VI Graph for filament lamp
how does current vary as voltage increases?
as more current flows in the lamp, the filament gets hotter, causing the resistance to increase. Doesnt obey ohm’s law
VI Graph for diode
how does current vary as voltage increases?
When connected in forward direction, diode has low resistance, allowing current to flow. When reversed, it has a high resistance and stops current flowing. Doesn’t obey ohm’s law
VI Graph for thermistor
how does current vary as voltage increases?
Thermistor is a semiconductor, conducting electricity when heated as more electrons are made available to carry current, decreasing the resistance. Doesn’t obey ohm’s law
VI Graph for LDR
how does current vary as voltage increases?
LDR is a semiconductor, conducting electricity when light shines on it, as more electrons are made available to carry current, decreasing the resistance. Doesn’t obey ohm’s law
which way does the current flow if battery is like this
———-|l———
<—
the steeper a VI graph, the _____ the resistance
lower
What is power
amount of energy transferred each second
energy (kWh) equation
E = P x t
power equation
P = V x I
cost of electricity equation
cost of electricity = kWh x cost per unit
