Download P6 student checklist 2017

OCR GCSE
Physics
Student checklist P6
Electricity for gadgets
Tick () red if you do not understand at all
Tick () amber if you are fairly confident
Tick () green if you know this and can use the equations
In your revision, focus on the red/amber columns.
Red
I can:
P6a
Amber
Draw the circuit symbol for resistor, variable resistor, bulb, cell, battery,
switch, and power supply.
State the units for voltage, current and resistance.
Explain that as the voltage increases for an ohmic conductor then current
increases.
Describe how the resistance of a wire increases when it gets hot.
Describe and explain how a variable resistor can be used in a circuit to
control current and to vary the brightness of a bulb or speed of a motor.
Use and manipulate the equation: resistance = voltage ÷ current.
P6b
Describe how a voltage–current graph can be used to find the resistance
of an ohmic conductor.
Describe how a voltage–current graph shows the changing resistance of a
non-ohmic device, such as a bulb.
Explain how the resistance is changed by changing the length of
resistance wire in a variable resistor.
Calculate the resistance of an ohmic conductor from a voltage–current
graph.
Explain the shape of a voltage–current graph for a non-ohmic conductor,
such as the filament in a lamp, in terms of how its resistance changes.
Describe how a potential divider circuit is used to produce a known pd in
a circuit.
Explain how two fixed resistors can be used as a potential divider.
Explain how one fixed resistor and one variable resistor in a potential
divider allows variation in the output pd.
Describe how the resistance of an LDR varies with light level.
Describe how the resistance of a thermistor varies with temperature.
Calculate the output pd of a potential divider from the values of its
resistors using: Vout =Vin x (R2)/R1 + R2
Explain how 2 variable resistors can be used in place of 2 fixed resistors
to provide an output pd with an adjustable threshold.
Explain why an LDR or thermistor can be used in place of R2 in a
potential divider with a fixed resistor to give an output signal which
depends on light or temperature
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Green
OCR GCSE
Physics
P6c
Student checklist P6
Calculate the total resistance of resistors in series and parallel.
1/Rt = 1/R1 + 1/R2 + 1/R3
Describe the benefits and drawbacks of increasing miniaturisation of
electronic components to manufacturers and users of the products.
Explain how increasing availability of computer power requires society
to make choices about acceptable uses of new technologies.
Be able to identify the base, collector and emitter in a transistor.
P6e
Understand how a small base current (Ib) is needed to switch on a greater
current flowing through the collector (Ic) ad emitter (Ie). Ie = Ib + Ic
Be able to label a circuit diagram showing how an NPN transistor can be
used as a switch for an LED.
Complete a labelled diagram to show how 2 transistors are connected to
make an AND gate.
Describe the truth tables for AND and OR logic gates in terms of high
and low signals.
Describe the truth table for NAND and NOR logic gates in terms of high
or low signals.
Describe the shape of the magnetic field around a straight wire,
rectangular coil or solenoid.
Describe that a current carrying wire at right angles to a magnetic field
experiences a force and can move.
Describe the effect of reversing the current and/or the direction of the
magnetic field.
Explain how the forces on a current-carrying coil in a magnetic field
make the coil turn and how this is used in a simple DC motor.
Describe the effect of changing the size of the electric current, the
number of turns on the coil and the strength of the magnetic field on the
rotation of the coil.
Describe how Fleming’s left-hand rule is used to predict the direction of
the force on a current carrying wire.
Describe the effect of changing –size of the current, number of turns on
the coil, strength of the magnetic field
Explain how a split-ring commutator maintains the direction of the force
on the coil in a DC electric motor.
Explain why practical motors have a radial field produced by curved pole
pieces.
P6f
Label a diagram of a DC generator.
Describe that a DC generator is a motor working in reverse.
Describe that in the UK mains electricity is supplied at 50 Hz.
Describe that a voltage is induced across a wire when the wire moves
relative to a magnetic field.
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OCR GCSE
Physics
Student checklist P6
Describe how a voltage is induced across a coil when the magnetic field
within it changes and describe the effect of reversing the direction of the
changing magnetic field.
Explain how the size of the induced voltage depends on the rate at which
the magnetic field changes.
Describe how an alternating current is generated when a magnet rotates
inside a coil of wire.
Describe that electricity in a power station is generated when an
electromagnet rotates inside coils of wire.
Describe how changing the speed of rotation of the electromagnet’s
coil(s) affects the size and frequency of the voltage generated.
Describe how changing the number of turns on the electromagnet’s
coil(s) affects the size of the voltage generated.
Explain, using a diagram, how an AC generator works including the
action of the slip rings and brushes.
P6e
Describe that transformers can change the size of an AC voltage.
State that transformers do not work with DC.
State that step-up transformers increase the voltage and step-down
transformers reduce the voltage.
Describe how step-up transformers are used at a power station to supply
the National Grid.
Describe how step-down transformers are used in sub-stations to reduce
the voltage for domestic use.
Describe that a transformer is made of two coils of wire wound on an
iron core and the difference between a step-up and a step-down
transformer.
State and manipulate the equation: Vp / Vs = Np / Ns
P6f
Describe that isolating transformers are used for safety reasons and
explain why.
Describe that power loss in the transmission of electrical power is related
to the square of the current flowing in the transmission lines.
Describe how a changing magnetic field in the primary coil induces an
output voltage in the secondary coil.
Explain why transformers use alternating current and how they can
change the size of an alternating voltage.
Explain that isolating transformers have equal numbers of turns on both
coils to limit the risk of contact between live parts and the earth lead.
Use and manipulate the equation: VpIp = VsIs applied to a transformer
and use this to explain why power is transmitted at high voltages.
Draw the symbols for a diode and a capacitor.
State that a diode only allows the current to flow in one direction and I
can tell the direction from the symbol.
Recognise half-wave and full-wave rectification from a voltage-time
graph.
Recognise and use the current–voltage graph for a silicon diode to
explain that a diode only allows current to flow in one direction.
Explain the graph for a silicon diode in terms of high and low resistance
in reverse and forward directions.
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OCR GCSE
Physics
Student checklist P6
State and recognise that a single diode produces half-wave rectification.
P6g
P6h
Describe and explain how four diodes can be used in the construction of a
bridge circuit to obtain full-wave rectification.
Describe what happens to an uncharged capacitor when a current flows in
a circuit containing an uncharged capacitor and that the capacitor stores
electrical charge.
State and recognise that a capacitor will produce a more constant
(smoothed) output and explain the action of a capacitor in a simple
smoothing circuit.
Describe the action of a silicon diode in terms of the movement of holes
and electrons.
Describe and explain the flow of current and the reduction in pd from a
charged capacitor when a conductor is connected across it.
State that the output of a logic gate is either high (about 5 V) or low
(about 0 V).
Describe that the output of a logic gate is high or low depending on its
input signal(s).
Describe the truth tables for NOT, AND and OR logic gates in terms of
high and low signals.
Describe how to use switches, LDRs and thermistors in series with fixed
resistors to provide input signals for logic gates.
Describe the truth tables for NAND and NOR logic gates in terms of high
and low signals.
Explain how a thermistor or an LDR can be used with a fixed resistor to
generate a signal for a logic gate that depends on temperature or light
conditions.
Explain how a thermistor or an LDR can be used with a variable resistor
to provide a signal with an adjustable threshold voltage for a logic gate.
Describe why a car alarm system requires a latch.
Recognise the symbol for a relay and explain that a relay can be used as a
switch.
Complete a truth table of a logic system with up to three inputs made
from logic gates.
Describe the use of an LED as an output for a logic gate.
Describe how a relay uses a small current in the relay coil to switch on a
circuit in which a larger current flows.
Explain how to work out the truth table of a logic system with up to four
inputs made from logic gates.
Describe how to connect NOR gates to make a bistable latch circuit.
Explain how, for a NOR gate latch:
(i) a brief high signal at one input results in a permanent high signal at the
latch output;
(ii) a brief high signal at the other input causes a low signal at the latch
output;
(iii) a low signal at both inputs leaves the latch output signal unchanged.
Explain how an LED and series resistor can be used to indicate the output
of a logic gate.
Describe that a relay is needed for a logic gate to switch a current in a
mains circuit because (i) a logic gate has a low power output and (ii) the
relay isolates the low voltage from the high voltage mains.
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This document may have been altered from the original.