P2-Electricity Flashcards
What is current?
The flow of electrical charge.
What is potential difference (voltage)?
Is the driving force that pushes the charge round.
What happens to the current when there is a great resistance?
The smaller the current that flows.
Total charge through a circuit depends on what?
Current and Time.
Formula for potential difference (V)?
Current (A) x resistance.
What are the 3 different types of graphs about Resistance and I-V characteristics?
Ohmic conductor.
Filament Lamp.
Diode.
Describe Ohmic conductors resistance?
Have a constant resistance.
Does some resistor’s resistance change?
Yes. Some resistors and components does change e.g. a diode or filament lamp.
What happens when an electrical charge flows through a filament charge?
It transfers some energy to the thermal energy store of the filament, which is designed to heat up.
What happens when the current in the filament lamp increases?
Resistance increases with temperature, so as the current increases, the filament heats up more and the resistance increases.
Describe the ohmic conductor? And graph?
The current through an ohmic conductor is directly proportional to potential difference. So you get a straight line.
Describe filament lamp? And graph?
As the current increases, the temperature of the filament increases, so the resistance increases. This means less current can flow per unit, so the graph gets shallower- hence the curve.
Describe diode? And graph?
Current will only flow through a diode in one direction. The diode has very high resistance in the reverse direction.
What is an LDR?
Light Dependant Resistor.
What is an LDR dependant on?
The intensity of light.
What happens to the light in an LDR in terms of the resistance?
In bright light, the resistance falls.
In darkness, the resistance is highest.
What is an LDR used for?
Applications including automatic night lights, outdoor lighting and burglar detectors.
What is a thermistor?
Is a temperature dependant resistor.
What does the resistance on a thermistor depend on?
Temperature.
Describe the resistance of a thermistor in different temperature?
In hot conditions, the resistance drops.
In cool conditions, the resistance goes up.
What are thermistors helpful for?
Temperature detectors, e.g. car engine temperature sensors and electronic thermostats.
Describe how series circuits are connected?
The different components are connected in a line, end to end, between +ve and -ve of the power supply.
What is potential difference sum in a series circuit?
Vtotal= V1 +V2.
What is the sum of current in a series circuit?
i1=i2=i3……
What is the resistance sum of series circuit?
R total = R1 + R2
Describe connections in parallel circuits?
Each components is separately connected to +ve and -ve of the supply.
What is potential difference sum in a parallel circuit?
V1 = V2 =……..
What is current sum in a parallel circuit?
I total = I1 + I2 + ……
What is the current for Mains supply and for Battery supply?
Mains supply is ac (alternating current).
Battery supply is dc (direct current).
What is the UK mains supply?
Is an ac supply at around 230 V.
What is direct current?
Is a current that’s always flowing in the same direction.
It’s created by direct voltage.
What are the 3 wires found in most electrical appliances?
Live wire.
Neutral wire.
Earth wire.
What are the colours of the 3 wires?
Live wire = brown.
Neutral wire = blue.
Earth wire = green and yellow.
What is live wire?
Provides the alternating potential difference (at about 230V) from the mains supply.
What is the neutral wire?
Completes the circuit and carries away current - electricity normally flows in through the live wire and out through the neutral wire. It is around 0 V.
What is the earth wire?
It is for protecting the wiring, and for safety - it stops the appliance casing from becoming live. It doesn’t usually carry a current - only when there’s a fault. It is at 0 V.
What can the live wire cause?
Electric shock.
How is energy transferred in electrical items?
Is transferred from cells and other sources.
What is potential difference in terms of energy transferred?
Is energy transferred per charge passed.
What does power depend on?
Current and potential difference.
How is electricity distributed?
Via the National Grid.
What is the National Grid?
Is a giant system of cables and transformers that covers the UK and connects power stations to consumers.
How does the National grid transfer energy?
Through power stations.
What is the Pd and low current like in the National grid?
High potential difference and low voltage.
What is the negative of high current?
You lose loads of energy as wires heat up and energy is transferred to the thermal energy store of the surroundings.
How is the Pd of the national grid changed?
By a transformer.
Describe the stages of energy stages through national grid?
Power station -> step-up transformer -> cables -> step-down transformer -> consumers.
What is a step-down transformer?
Converts high voltage to low. And low current to high.
What is a step-up transformer?
Converts high voltage to low. And low current to high.
