Electricity Flashcards
Define electric current
rate of flow of charge
What does electric current of one amp represent?
rate of flow of charge of one coulomb per second
Name the instrument used to measure current
ammeter
Define potential difference
V = W/ Q
Name the instrument used to measure the p.d between two points in a circuit
voltmeter
What is the resistance of a component and how is it defined?
measure of how much a component opposes the flow of current
R = V/I
State Ohm’s law
current through a metallic conductor is directly proportional to the p.d across it, provided physical conditions do not change
What is the name for a conductor that obeys Ohm’s law?
ohmic conductor, constant resistance
What is the I-V characteristic of a component?
graph which shows how the current through the component varies with the p.d across it
Describe the I-V characteristic for an ohmic conductor
straight line graph through the origin
Describe the I-V characteristic for a filament lamp
curve with decreasing gradient
Describe the i-v characteristic of a diode
with forward bias, graph starts at 0,0 and increases gradually, with reverse bias hrap extends along the negative p.d with almost 0 current
What is a negative temperature coefficient thermistor?
Component for which resistance decreases with higher temperatures
What is a superconductor?
material with zero resistivity at and below a certain temperature
Why are superconductors useful?
Current has no heating effect so no energy lost
State the law of conservation of charge
charge cannot be created or destroyed, so the amount of charge in a closed system remains the same
State Kirchhoff’s first law
Total current leaving a junction = total current entering junction
Define the potential difference between two points in a circuit
energy transferred per coulomb of charge that flows from one point to the other
What is potential drop in a circuit?
p.d between two points in a circuit if the charge carriers lose energy
State Kirchhoff’s Second law
sum of the emfs around any loop in a circuit = sum of p.ds around the loop
Give the potential difference rule for two or more components in series
total p.d across all the components = sum of the potential differences across each component
What can a potential divider circuit do as part of a sensor circuit?
supply a p.d that varies with physical conditions
What is a potentiometer?
variable potential divider that uses a single variable resistor to allow Vout to be varied from 0V to the maximum source p.d
Define the electromotive force of a power supply and give its unit
electrical energy per unit charge produced by the power source, volts
Give the equation relating to emf of a power supply to its internal resistance, the current in the circuit, and the external resistance
emf = I(R+r)
Give the equation for calculating lost p.d across a power supply’s internal resistance
lost p.d = Ir
What is the benefit of connecting cells in parallel?
providing longer-lasting energy supply because the total energy store is greater
