# P6

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unit of voltage?
volts
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unit of current?
amps
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unit of resistance?
ohms
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voltage =
current x resistance
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what does a high resistance mean?
low current
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what does a dimmer switch have?
a contact that moves around a circular coil of wire
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what factors affect the resistance?
length, cross sectional area and material its made from
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what is the voltage across a component sometimes referred to?
potential difference
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how do you calculate Vout?
(r2 / r1 + r2) x Vs
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total resistance in series =
Ra + Rb + Rc
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in a thermistor - as temperature increases what decreases?
resistance decreases
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what do street lamps use?
potential divider circuits with an LDR in
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when its dark what does the LDR have? and what does this mean?
very high resistance meaning the potential difference is high and can be used to switch on a light
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what is a way a variable output can be obtained without setting up a new circuit each time?
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how does a current flow across?
from a collector to the emitter
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Ie =
Ib + Ic (I=current, e =emitter, b=base, c=collector)
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why is the resistor above the LED?
to limit the current so the LED doesnt become too hot and break
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not gates
the output is opposite to the input
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and gates
the output is 1 when both inputs are 1
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or gate
the output is 1 if either of the inputs is 1 or both
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nand gate
the ouput is only 0 when both inputs are 1
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nor gate
the output is only 1 when both inputs are 0
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what is a relay operated by?
the output current from a logic gate
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what is a relay designed to use?
a low current in the coil to switch a larger current in another circuit
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what can be connected together to make a bi-stable latch?
two nor gates
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flemings left hand rule for motors
thumb = motion, index = force, second finger = current
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where do electric motors transfer energy to?
the load and to the surroundings
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what ring do motors use?
split-ring
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how does a split ring commutator keep the motor spinning in the same direction?
when the coil moves past the vertical, the opposite sides of the split ring connects with the opposite brush so the current is reversed
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what can you do to reverse the direction of the force on the bar?
reverse current or reverse polarity of magnet
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what can you do to increase the magnitude of the force on the bar?
stronger magnet or bigger current
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what can make an electric motor spin faster?
having more turns on the coil / using a stronger magnetic field / using a soft iron core / using a bigger current
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what is the effect of reversing the direction of the changing magnetic field?
the direction of the voltage and current will reverse
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what happens when the coil rotates faster?
it will cut the magnetic field faster, therefore the output voltage will be bigger
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when is alternating current produced?
when the coil rotates in the field
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what is a generator?
a generator is a device that converts mechanical energy into electrical energy
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do rotor coils move or stay still?
moves
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do stator coils move or stay still?
stay still
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what happens when speed of turning the coil changes?
if you rotate the magnet faster, you will get a higher peak voltage but it will also be a higher frequency; this is because the magnetic field is reversing more often
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how is electricity generated at a power station?
an electromagnet rotates inside coils of wire
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what rotates in a generator in a power station?
and electromagnet
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what type of current does a generator in a power station generate?
AC (alternating current)
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why dont AC generators have split-ring commutators?
split-rings swap contact every half turn giving you direct current not AC
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step-up transformers have more turns on which coil?
the secondary coil
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more turns on the secondary coil allow what?
the voltage to be increased, this decreases the current
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why do transformers only work with AC?
they need to produce a changing magnetic field in the core
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why are step-up transformers used?
to reduce heat loss
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why are step-down transformers used?
make safe amount of voltage for houses
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what does the changing magnetic field in the core induce?
a changing voltage in the secondary coil
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what are isolating transformers used for?
safety because there is no earth pin and therefore cant receive an electric shock when water or steam touches it
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do isolating transformers have the same number of turns on the primary and secondary coils?
yes
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do isolating transformers change the voltage in a circuit?
no
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what does the n-type semi-conductor have?
an excess of electrons
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what does the p-type semi conductor have?
a shortage of electrons
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what is the region callled where holes from the p-type half are repelled by the positive ions in the n-type area?
the depletion layer
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why is there no current in the depletion area?
because of the lack of electrons and holes
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what is a diode?
a component that only allows electric current to flow in one direction
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what is it when the diode is forward biased?
current passing easily through the diode (low resistance)
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what is it when the diode is reverse diode?
there is almost no current
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## Other cards in this set

unit of current?

amps

### Card 3

#### Front

unit of resistance?

voltage =

### Card 5

#### Front

what does a high resistance mean?