Electricity Flashcards
What is static electricity?
When charge “builds up” on an object and then stays static.
How does static electricity cause objects to attract? (3)
- electrons are rubbed off one material and on the other.
- the material that gains electrons becomes negatively charged and the material that loses electrons becomes positively charged
- they attract
Describe the IV characteristic graph for a fixed resister
Current is directly proportional to the potential difference across the resistor. This means resistance remains constant as current changes.
Describe the IV characteristic graph for a filament lamp
The resistance of a filament lamp increases as the temperature of the filament increases. S shaped graph(does not go down)
Describe the IV characteristic graph for a diode
The current through a diode flows in one direction only. The diode has a very high resistance in the reverse direction.
What do LDR and thermistors do and how does it affect resistance?
LDR: light energy is absorbed creating more free electrons
Thermistor: heat energy is absorbed creating more free electrons
The free electrons mean more current so resistance decreases as light intensity/ temperature increases.
What happens if there is too much static electricity?
Too much static electricity can cause a spark. If the potential difference is large enough, the electrons can jump across the gap to an object that is neutral.
What are the laws about potential difference, resistance and current in a series circuit?
-Potential difference of the power supply is shared between components.
- The resistance of the components add to get the total resistance.
-The current is the same through each component
What are the laws about potential difference , resistance and current in a parallel circuit?
Potential difference is the same through all components.
Current is shared between components.
The total resistance is less than the smallest resistor.
What happens when resistors are added in parallel?
The total resistance decreases and is lower than the lowest resistor. This is because voltage is the same for every component, but there are more paths for current to pass through, meaning more current. This decreases resistance.
What is AC current?
The current changes direction continuously. E,g mains supply
What is DC current?
current only flows in one direction
What is the national grid?
A system of power cables and transformers connected across the country to power stations so electricity can reach consumers.
How can energy loss be reduced when electricity is transmitted over long distance
Using a step up transformer. This increases voltage but decreases current so that energy is not lost to heat (because high current equals high resistance)
What colour are the wires in a plug and what do they do?
Brown- live wire, carry alternating voltage from the mains supply to the circuit.
Blue- neutral wire, completes circuit
Green/yellow- earth wire, only carry’s current if there is a fault
How do the earth wire and Duse prevent the mains cable from heating?
Current will go from live wire to earth wire (rather than through circuit). Because it doesn’t go through components, current is high as resistance is low. The high current melts the fuse, breaking the circuit.
