Energy, Power and Resistance Flashcards
How are Kirchoff’s laws applied to series circuits?
- current same everywhere
- EMF shared across components
How are Kirchoff’s laws applied to parallel circuits?
- current splits across branches
- voltage same everywhere
How is resistance calculated in series circuits?
resistance of resistors added up
How is resistance calculated in parallel circuits?
Rt = (1/r1) + (1/r2) etc
How does resistance restrict the flow of charge?
repeated collisions between charge carriers and other materials
What is ohms law?
potential difference is directly proportional to current as long as temperature is constant
Define resistance:
the potential difference needed to make 1 ampere of current flow
What are the IV characteristics of a fixed resistor?
- directly proportional
- steeper gradient = less resistance
What are the IV characteristics of a filament lamp?
- non ohmic
- as current increases heating effect on metal ions causes resistance to increase
What are the IV characteristics of diodes?
- resistance rapidly decreases as potential difference is above threshold value as number density of charge carriers increases
- anything other than positive I or V the resistance is too high therefore no current flows
What are the IV characteristics of thermistors?
resistance decreases as temperature increases
What are the IV characteristics of LDRs?
resistance decreases as light intensity increases
What are sensors?
component that allows a physical quantity to change its resistance
What can change depending on an LEDs colour?
threshold PD
Define resistivity:
materials opposition to the flow of charge
What is the relationship between resistance and resistivity?
directly proportional
What is the relationship between resistance and length of wires?
directly proportional
What is the relationship between resistance and cross sectional area of a wire?
inversely proportional
What is transferred when there is current in a component?
energy
What is an electricity meter?
records transfer of energy from national grid to house
What does the cost of electricity depend on?
power and duration of device used
Define kilowatt hour:
energy transferred by a device of power 1kW operating for a time of 1 hour
What does 1kWh equal?
3.6MJ
What is the average cost per kWh?
6-15p
