# P6 - Physics GCSE revision

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• Created by: Beth
• Created on: 05-06-13 18:59
what happens to the current if the voltage increases in an ohmic conductor?
the current also increases
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what can make a wire have more resistance?
if the wire gets hot or if the wirer is longer/very long
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what is a variable resistor used for in a circuit?
to control the current and to vary the brightness of a bulb or vary the speed of a motor
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what is resistance measured in?
ohms
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how do you find the resistance (of a component)?
you take the gradient of a voltage-current graph
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what does a steeper line show on a voltage-current graph?
it shows a HIGHER RESISTANCE
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what does a curved line show on a voltage-current graph?
it shows a CHANGING RESISTANCE
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what is potential difference another name for?
voltage
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what happens to the resistance of an LDR as the light level increases?
the resistance decreases
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what happens to the resistance of a thermistor as temperature increases?
the resistance decreases
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what is a potential divider circuit used for, and how is the circuit done?
it is used to produce a known potential difference (pd)in a circuit and is done by connecting two fixed resistors in series
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what is the formula to calculate the output voltage?
Vout = Vin x R2 / (R1 + R2) R1 = resistance of 1st resistor R2 = resistance of 2nd resistor
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if a potential divider is made from 1 fixed resistor, and 1 variable resistor, what can you do?
you can vary the output pd(voltage)
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if a potential divider is made from 1 fixed resistor, and 1 LDR, what does the output voltage depend on?
the light level
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if a potential divider is made from 1 fixed resistor, and 1 thermistor, what does the output voltage depend on?
the temperature
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what is the output of a logic gate?
either high or low, on or off, 1 or 0
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what does the output of a logic gate depend on?
depends on it's input signal(s)
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what is the rule for an AND gate?
both the inputs have to be 1 to get 1 out
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what is the rule for an OR gate?
at least one of the inputs have to be 1 to get 1 out
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what is the rule for a NOT gate?
the output is always the opposite of the input
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what is the rule for a NAND gate?
you do the AND gate and then take the opposite
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what is the rule for a NOR gate?
you do the OR gate and then take the opposite
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what can an LDR or a thermistor be used to generate (to do with logic gates)?
they can be used to generate a signal for a logic gate that depends on temperature or light conditions
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when light intensity increases, what happens to the resistance of an LDR and what happens to the output?
the resistance decreases, so the output goes high
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what happens to the resistance of a thermistor when temperature increases and what happens to the output?
the resistance decreases, so the output goes high
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what can an LED be in terms of logic gates?
an LED can be an input or an output for a logic gate
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how do you work out a logic gate question with up to 4 inputs?
you look at each gate seperately
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what can a relay be used for?
a relay can be used as a switch
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how does a relay work?
it uses a small current in the relay coil to switch on a circuit in which a larger current flows
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why do logic gates need relay circuits?
because they use a low voltage
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why does a car alarm system require a latch?
because you want the alarm to keep sounding even after the sensor has been triggered
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in a bistable latch, what does a breif high signal at one INPUT result in?
it results in a permanent high signal at the latch output (alarm on)
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in a bistable latch, what does a breif high signal at the other INPUT (reset) cause?
it causes a low signal at the latch output (alarm off)
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in a bistable latch, what does a low signal at both inputs do?
it leaves the latch output signal uncharged
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what do you need to make a complete motor?
electricity, a coil of wire and a magnetic field to make movement
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what is a solenoid?
a coil of wire
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if you put a wire at right angles to a magnetic field and pass current through it, what will happen?
it will make the wire current carrying, and it will experience a force that will make it move
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what is Flemming's left hand rule used for?
it is used to predict the direction of the force on a current carrying wire
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in Flemming's left hand rule, what does the thumb, first finger and second finger show?
thumb: direction of the force/motion first finger: direction of the field seconf finger: direction of the current
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what direction do magnetic fields always go in?
from North to South
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if you reverse the magnetic field or the current, what will happen?
the force will reverse
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if you have a coil of wire with current flowing through it in a magnetic field, what will happen?
the forces will make it spin
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how can you make a motor spin faster?
you can make the magnet stronger, increase the current, or increase the number of coils
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what does a split-ring comutator do in a DC electric motor?
it maintains the direction of the force on the coil
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why do real motors have a radial field produced by CURVED pole pieces?
because it concentrates the magnetic field
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how do you make electricity in a generator?
you need movement, a coil of wire and a magnetic field (this is also called the dynamo effect)
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what do you do if you change the direction of the magnetic field?
you change the direction of the induced voltage as well
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what happens if you start to move the wire more quickly?
you increase the induced voltage
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what is a DC generator?
a motor working in reverse
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does a DC generator have a split ring commutator?
YES
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what other type of generator can you get?
one where the magnet spins inside the coil of wire, this type of generator makes an ALTERNATING CURRENT
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what happens,the quicker the magnet spins in a generator?
the higher the induces voltage and the higher the frequency
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in a power station, electricity is generated by what?
an electromagnet rotating inside coils of wire
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in the UK mains electricity is supplied at what?
50Hz
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what do the split rings and brushes allow in a generator?
they allow the generator to spin without tangling the wires
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what can transformers do?
change the size of an AC voltage
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what do step-up and step-down transformers do?
step-up: increase the voltage step-down: decrease the voltage
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where are step-up transformer used?
at power stations before the voltage goes to the power lines
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where are step-down transformers used?
in sub-stations to reduce the voltage for domestic use
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what is a transformer made of?
two coils of wire (primary and secondary coil) wound on an iron core
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explain step-up and step-down transformers in terms of the primary and secondary coils?
in step-up transformers, there are more turns on the secondary coils, in step-down transformers, there are more turns on the primary coil
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what is the formula to find the output voltage from a transformer?
Vp / Vs = Np / Ns
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what do Vp, Vs, Np and Ns stand for?
Vp - voltage in the primary coil, Vs - voltage in the secondary coil, Np - number of primary turns, Ns - number of secondary turns
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what are isolating transformers and what are they used for?
transformers that have the same number of turns on both sets of coils and are used for safety reasons as they prevent the user from coming into contact with live parts
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what is power loss in the transmission of electrical power related to?
it is related to the current flowing in the transmission lines (if current doubles, power loss quadruples)
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why do transformers use AC?
because this type of current makes a moving magnetic field
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what does a diode do?
allows current to flow in one direction
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what is half wave rectification caused by?
putting AC through a diode
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if a graph to show charge is really steep, what does it mean?
the graph shows low resistance in the forward direction
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if a graph to show charge is horizontal, whats does it mean?
the graph shows high resistance in the reverse direction
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when will an uncharged capacitator charge up (store charge)?
when a current flows in its circuit
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what can four diodes be used for?
they can be used in the construction of a bridge circuit to obtain full-wave rectification
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when will a circuit discharge(let its charge out)?
when a circuit is connected across a charged capacitator
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how will a capatcitator produce a more constant (smooth) output in half-wave rectification?
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why do diodes work?
because one side has extra electrons and the other has extra holes which move
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## Other cards in this set

### Card 2

#### Front

what can make a wire have more resistance?

#### Back

if the wire gets hot or if the wirer is longer/very long

### Card 3

#### Front

what is a variable resistor used for in a circuit?

### Card 4

#### Front

what is resistance measured in?

### Card 5

#### Front

how do you find the resistance (of a component)?