AQA Combine Physics 6.2 Flashcards
Revision for Paper 1
Describe an I-V graph for a diode
Current will only flow in one direction (there is a very high resistance in the other direction)
Describe an I-V graph for an ohmic resistor (e.g. resistor at a constant temperature)
Current (at constant temperature) is directly proportional to potential difference
What happebs to the resistance of an ohmic conductor (such as a wire) when the current changes?
The resistance of ohmic conductors doesn’t change with current
For a given potential difference, what happens to the current when the resistance increases?
The current gets smaller
In a single closed loop, what value would the current have at any point?
The same value
What is electrical current and what determines the size of the current?
The flow of electrical charge, determined by the rate of flow
What are the two ways of joining an electrical component?
In series or in parallell=
Where are LDRs commonly found?
LDRs are used as automatic night lights/burglar detectors
Where are thermistors commonly found?
Car engine temperature sensors/electronic thermostats
Describe direct current supplies
Current that is always flowing in the same direction (created by a direct voltage)
What type of electricity supply is mains?
Alternating current (AC)
How can the total current through a parallel circuit be calculated?
It is the sum of the currents through the separate components
What is the equation for Rtotal?
Rtotal = R1 + R2
What equation links power, current and potential difference?
Power = current x potential difference P = I V
What equation links power, current and resistance?
Power = current 2 x resistance P = I2 R
What is the function of the Earth wire (green/yellow)?
Acts as a safety device, stopping the appliance casing from becoming live (OV)
What is the function of the live wire (brown)?
Provides the alternating potential difference (230V)
Describe the characteristics of the UK mains supply
230V AC with a frequency of 50Hz
How are step-up transformers used within the National Grid?
Step-up transformers increase the potential difference of the National Grid to 400,00V
What does the National Grid comprise of?
A system of cables and transformers linking power stations to consumers
What effects of the power of a circuit?
- The potential difference and current which runs through it
- The energy transferred over a given time
What is ‘done’ when change flows in a circuit?
Work (done)
How can the gravitational potential energy of an object raised above the ground be calculated?
Gravitational Potential Energy = mass x gravitational field strength x height
Ep = m g h
What is a three-core cable?
Three wires (core of copper) with a brown (live wire), blue (neutral wire) and green/yellow (Earth wire)
How is the National Grid made as a efficient as possible?
A high potential difference and a low current which, for a given power, decreases energy lost by heating (the wires / surroundings)
In the UK, how is electricity distributed?
Via the National Grid
How can the live wire cause an electric shock?
Touching a live wire (230V) puts a large potential difference across your body (OV) which can shock / kill
What is the function of the neutral wire (blue)
Completes the circuit carrying current away (OV)
In a parallel circuit what is the potential differences across each component like?
It is the same
What would the total resistance of two resistors be?
Less than the resistance of the smallest individual resistor
What type of electricity supply is a battery?
Direct current (DC)
What happens to the resistance of a LDR as light increases?
As light increases a LDR’s resistance decreases
How are LDRs and thermistors used in sensing circuits?
Sensing circuits can be used to turn on / increase the power to components depending on conditions
In a series circuit, what is the current like through all components?
The same
What happens to the resistance of a diode or filament lamp when current changes?
Resistance increases with temperature, such as the current increases the resistance increases
Describe an I-V graph for a filament lamp
As the current increases the temperature of the filament lamp increases meaning less current can flow per unit potential diffrence
For electrical charge to flow through a closed circuit what must be included?
A source of potential difference
What is the equation for charge flow?
Charge flow = current x time
Q = I t
How are the step-down transformers used within the National Grid?
Step-down transformers bring the 400,000V of the National Grid down to 230V for domestic use
What determines how much energy an appliance transfers?
How long the appliance is on for and the power of the appliance
Describe alternating current supplies
Current which constantly changes direction
What happens to the resistance of a thermistor as temperature increases?
As temperature increases a thermistor’s resistance decreases
How can the total resistance of two components in a series circuit be worked out?
The total resistance of the components in a series circuit is the sum of all of them
What affects the current through a given component?
The resistance of the component and the potential difference across it
How is the total potential difference distributed between the components in a series circuit?
It is shared
What equation links energy transferred, power and time?
Energy transferred = power x time
E = P t
What equation links energy transferred, charge flow and potential difference?
Energy transferred = charge flow x potential difference
E = Q V
What equation links potential difference, current and voltage?
Potential difference = current x resistance
V = I R
