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paper 2
topic 10- electricity and circuits
resistance
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Charlotte
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Cards (14)
how does resistance affect current in a circuit?
as total
resistance
of circuit
increases
current
flowing through circuit
decreases
how can the current in a circuit be varied?
use a
variable
resistor
give the equation linking current and resistance
V =
IR
how is total resistance affected by two resistors in series?
total
resistance
increases
equal to the
sum
of the two
resistors
how is total resistance affected by two resistors in parallel?
total
resistance
decreases
less than
resistance
of the resistor with the
lowest
resistance
what is an
Ohmic
conductor, state the condition required
conductor for
current
+
potential difference
=
directly
proportional
resistance
remains
constant
as
current
changes
temperature
must be constant
list 4 components in which resistance is not constant as current changes
filament
lamps
diodes
thermistors
light dependent
resistors (LDRs)
what happens to the resistance of a filament lamp as the temperature increases? Why?
resistance
increases
metal
ions
= more
kinetic
energy:
vibrate
more,
colliding
more frequently with
electrons
as they flow through
metal
creates more
resistance
to current flow
what is different about current flow through a diode?
current only flows in one
direction
resistance
= very high in
other
direction, preventing
current
flow
state what happens to the resistance of a thermistor as temperature increases
thermistor's resistance decreases
give examples of when a thermistor may be used
in a
thermostat
: turn a
heater
on below a certain
temperature
in a
freezer
: turn on a
cooler
when temperature = too
high
state what happens to the resistance of an LDR as light intensity decreases
LDR's resistance
increases
give applications for an LDR
street
lamps or
night
lights
when light levels
drop
(night),
resistance
and the light gains
sufficient
current
to turn on
how do diodes work?
only allows current to flow in one
direction
if current is flowing the
right
way,
resistance
is large for small voltages (up to
0.6 V
)
but then at higher voltage becomes very
small