Current of Electricity Flashcards
Definition of “number density”
The number density n is defined as the number of particles per unit volume
Definition of drift velocity
The drift velocity v is the average velocity at which charge carriers move through a conductor when there is electric current in the conductor
Definition of “current”
Current is defined as the rate of flow of charges
What is another formula for current apart from I = Q/t and how do you derive that from I = Q/t?
I = nAvq
I = Q/t
Q = Nq
N = nV
V = AΔx = Avt
combining together -> I = nAvq trust
Definition of a coulomb
One coulomb is the amount of charge that flows through a given cross section of a circuit in one second when there is a constant current of one ampere
Definition of potential difference
The potential difference V between 2 points of a circuit is defined as the amount of electrical energy converted to other forms of energy per unit charge moved between these 2 points
V = W/Q
Definition of a volt
The volt is defined as the pd between 2 points of a conducting wire when 1 coulomb of charge loses 1 joule of energy between those points
What is Ohm’s Law?
Ohm’s Law states that the current flowing in a conductor is directly proportional to the pd across it under constant physical conditions (eg temp, incident light intensity etc) i.e. I ∝ V
Definition of resistance (clue: literally just define R = V/I)
Resistance is defined as the ratio of the potential difference across the conductor to the current flowing through it
What is another formula for resistance?
R = ρL/A
What are the characteristics of a METALLIC CONDUCTOR as constant temperature?
- it is an ohmic conductor
- it has constant resistance
explanation:
1. at constant temperature, the number of free electrons and the rate of atomic vibration remains unchanged
What are the characteristics of a SEMICONDUCTOR DIODE (non-ideal) as constant temperature?
forward based:
1. as pd increases, resistance decreases. if pd crosses threshold voltage, resistance will become very low (nearly zero)
reverse-based:
1. very high resistance however still have a small leakage current
2. if pd is so high that it goes past its breakdown voltage, the diode will breakdown and conduct electricity
What are the characteristics of a filament lamp? (affected by changes in temperature)
The resistance R increases with increase in temperature T.
What are the characteristics of a Negative Temperature Coefficient Thermistor? (affected by changes in temperature)
The resistance R decreases with an increase in temperature
Explanation:
As current increases, power dissipated increases. As amount of heat increases, so equi temp increases.
As temperature increases, the mean KE of the particles increases. This will result in:
1. bonded electrons breaking free from their bonds (increasing number of mobile charge carriers) -> lowering resistance
2. Lattice ions vibrate more vigorously, hindering flow of mobile charge carriers -> increasing resistance
BUT 1. is more significant than 2. So the overall effect is a decrease in resistance.
Definition of emf (electromotive force)
The emf of a source is defined as the amount of energy transferred from non-electrical forms of energy to electrical energy per unit charge as the charge passes through a complete circuit.
emf = W/Q
!! W is the TOTAL work done across the entire circuit !!
