Combined Physics - 6.2 Flashcards
What are the circuit symbols for a switch (open and closed), a cell and a battery?
What are the circuit symbols for a diode, resistor, variable resistor and LED?
What are the circuit symbols for a lamp, fuse and voltmeter?
What are the circuit symbols for an ammeter, thermistor and LDR?
For electrical charge to flow through a closed circuit what must be included?
A source of potential difference
What is electrical current and what determines the size of the current?
The flow of electrical charge, determined by the rate of flow
What is the equation for charge flow?
In a single closed loop, what value would the current have at any point?
The same value
What affects the current through a given component?
The resistance of the component and the potential difference across it
For a given potential difference, what happens to the current when the resistance increases?
The current gets smaller
What equation links potential difference, current and voltage?
What happens 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
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
Draw and describe an I-V graph for an ohmic resistor (e.g. a resistor at a constant temperature)
Current (at constant temperature) is directly proportional to potential difference
Draw and describe an I-V graph for a filament lamp
As the current increases the temperature of the filament lamp increases (so the resistance increases) meaning less current can flow per unit potential difference
Draw and 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)
What happens to the resistance of a thermistor as temperature increases?
As temperature increases a thermistor’s resistance decreases
Where are thermistors commonly found?
Car engine temperature sensors / electronic thermostats (as temperature rises the resistance decreases)
What happens to the resistance of a LDR as light increases?
As light increases a LDR’s resistance decreases
Where are LDRs commonly found?
LDRs are used as automatic night lights / burglar detectors (in bright light the resistance is low)
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 (e.g. as a room gets hotter the resistance of a thermistor decreases taking a smaller share of the potential difference from a power supply allowing a fan to get more potential difference and spin faster)
What are the two ways of joining an electrical component?
In series or in parallel
In a series circuit, what is the current like through all components?
The same
How is the total potential difference distributed between the components in a series circuit?
It is shared
How are 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
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
In a parallel circuit what is the potential difference 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 is the equation for Rtotal?
Rtotal = R1 + R2
How can the total current through a parallel circuit be calculated?
It is the sum of the currents through the separate components
What type of electricity supply is mains?
Alternating current (AC)
Describe direct current supplies
Current that is always flowing in the same direction (created by a direct voltage)
Describe alternating current supplies
Current which constantly changes direction
What is a three-core cable?
Three wires (core of copper) with a brown (live wire), blue (neutral wire) and green / yellow (Earth wire)
What is the function of the neutral wire (blue)
Completes the circuit carrying current away (OV)
How can the live wire cause an electric shock?
Touching a live wire (230V) puts a large potential difference across your body (0V) which can shock / kill
Describe the characteristics of the UK mains supply
230V AC with a frequency of 50Hz
What is the function of the live wire (brown)?
Provides the alternating potential difference (230V)
What is the function of the Earth wire (green / yellow)?
Acts as a safety device, stopping the appliance casing from becoming live (OV)
Q. What equations links power, current and potential difference?
Q. What equation links power, current and resistance?
Power = current x potential difference
P = I V
Power = current2 x resistance
P = I2 R
What determines how much energy an appliance transfers?
How long the appliance is on for and the power of the appliance
Q. What equation links energy transferred, power and time?
Q. What equation links energy transferred, charge flow and potential difference?
Energy transferred = power x time
E = P t
Energy transferred = charge flow x potential difference
E = Q V
In the UK, how is electricity distributed?
Via the National Grid
How is the National Grid made as efficient as possible?
A high potential difference and a low current which, for a given power, decreases energy lost by heating (the wires / surroundings)
What is ‘done’ when charge flows in a circuit?
Work (done)
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 does the National Grid comprise of?
A system of cables and transformers linking power stations to consumers
How are step-up transformers used within the National Grid?
Step-up transformers increase the potential difference of the National Grid to 400,000V
