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 !!
Tutorial Question: When a domestic lighting circuit is switched on, the lights come on almost immediately. Explain this.
The drift velocity due to the movement of electrons that will cause the light to turn on, but it is the electric field being established that causes the electrons to start moving, so all the electrons start moving almost instantaneously.
What are some safety precautions that can be taken when handling electric wires?
- ensure circuit is open before handling
- wear gloves
