Electric Current Flashcards
(20 cards)
What is an Electric Current?
Rate of flow of charges through a cross-sectional area in a particular direction.
I = q/t (Coulomb/Second)
What is Drift Velocity?
Final average velocity of all the electrons in the conductor, under the effect of an electric field.
Vd = -eEτ/m
What is Relaxation Time?
The time between two successive collisions of an electron. Denoted by τ.
What is Mobility?
Drift velocity of charge per unit applied electric field.
μ = eτ/m (Conductor)
μ = qτ/m (General Formula)
SI unit : m²/s¹v¹ or mC/s¹N¹
What is Ohm’s Law?
Current flowing through a conductor is directly proportional to the potential difference applied given that the temperature, pressure, and mechanical stress are constant.
V = IR
What is Resistance?
Property of a conductor to oppose the flow of the electric current.
R = V/I
R = (m/ne²τ) (l/A)
DF = M¹L² / T³A²
What is Resistivity?
Nature of the material from which the conductor is made.
What is Current Density?
Amount of current flowing per unit area.
J = I/A
I = JA
What is Conductance?
The property of a conductor with the charges flows with ease.
G = 1/R
What is Conductivity?
Nature of the material to aid the flow of charges.
σ = 1/ρ
What is the Temperature Coefficient?
The temperature coefficient is the increase in resistance/resistivity per unit of original resistance/resistivity per degree rise in temperature.
R(T) = R(o) [1+ α (∆T)]
Unit : 1/C°
What is Kirchoff’s first law?
The current meeting at a junction is always zero.
Sum of incoming current = Sum of outgoing current.
What is Kirchoff’s second law?
The sum of all the voltage differences in a circuit is zero.
V(1) + V(2) + V(3)……..= 0
What is a Wheat Stone Bridge?
It states that if four resistances are connected to form a bridge and the bridge is balanced then their ratios are equal.
P/Q = R/S
What is a Cell?
Device to maintain steady current in electric current and is called electromotive force (ε) when not connected to a circuit.
It also has an internal resistance (r) offered by its electrode and electrolyte.
What is Terminal Potential Difference?
The actual potential difference of the cell minus the potential used by its internal resistance.
V(AB) = V(A) - V(B) = ε - Ir
What are Non - Ohmic devices?
Objects which don’t obey ohm’s law and the following conditions:
1) Has a unique relation for VI.
2) The graphs of V&I are linear.
3) When the magnitude stays the same after changing direction.
What is the Heating effect of current?
When an electric current is passed through a conductor, it generates heat due to the resistance in the conductor.
H = VIT = I²RT = V²T/R
P = VI = I²R = V²/R
Why are alloys used for making standard resistance coils?
Alloys have a small value of the temperature coefficient of resistance with less temperature sensitivity. This keeps the resistance of the wire almost constant and they also have high resistivity for given L and A of conductor
What is the significance of the direction of electric current?
The flow of electric current is caused by the free electrons in the conductor but the direction is taken in the opposite direction of the flow of free electrons.
