Module 4.2 - Electricity: Energy, Power and Resistance Flashcards
What is potential difference?
The energy transferred per unit charge across a COMPONENT
What are the units of potential difference?
Volts or J/C
Define electromotive force
Energy gained per unit charge by charges passing through SUPPLY
What is the difference between e.m.f. and p.d.?
e.m.f. is the energy transferred to each unit charge from a SUPPLY, p.d. is the energy transferred by each unit charge to a COMPONENT.
How do you work out the energy transferred to each unit charge from a supply using the e.m.f?
Work done = em.f. x charge
How do you work out the energy transferred by each unit charge to a component using p.d.?
Work done = p.d. x charge
W = VQ
How is the energy transferred to each charged particle, eV, calculated?
eV = 1/2mv^2
e - charge of electron
V - p.d.
m - mass of electron
v - velocity of electron
What is Ohm’s law?
Current through a conductor is DIRECTLY PROPORTIONAL to the potential difference across it
What is Ohm’s law in equation form?
V = IR
What is the unit of resistance?
Ohm - Ω
What are the 4 factors that affect resistance?
> Material
Length of wire
Cross-sectional area
Temperature
How does the material affect resistance ?
Different electrical properties
How does the length of wire affect resistance?
As length increases, resistance increases - therefore current decreases.
How does the cross-sectional area of the wire affect resistance?
As area increases, resistance decreases - current increases
How does temperature affect resistance?
As temperature increases, resistance increases
What are ohmic conductors?
Conductors that obey Ohm’s law
What type of property is resistivity and what is not affected by?
An intrinsic property that is not affected by physical dimension
How do you work out the resistance of a material using its resistivity?
R = (p x L) ÷ A
What is resistivity affected by?
Temperature
How are the resistivity of metals affected by temperature?
As temperature increases, resistivity increases
How are the resistivity of some semiconductors affected by temperature?
As temperature increases, the resistivity decreases
What is an NTC thermistor?
Negative temperature coefficient thermistor - as temperature increases, resistance decreases
What is a PTC thermistor?
Positive temperature coefficient - as temperature increases, resistance decreases
How do you work out power using current and voltage?
P = VI
How do you work out power using current and resistance?
P = I^2 x R
How do you work out power using voltage and resistance?
P = V^2 ÷ R
How do you work out the electrical work done using charge and voltage?
W = QV
How do you work out electrical work done using current, voltage and time?
W = V x I x t
What is a kW h?
> Unit of energy
> 1000 watts for 3600 secs = 3,600,000J
How you convert from J to kW h?
÷ 3,600,000
How do you convert from kW h to J?
x 3,600,000
