CURRENT ELECTRICITY Flashcards
The motion of free electrons inside conductor is
random motion
what is drift velocity?
the uniform velocity gained by free electrons of conductor when it is attached with the battery of certain voltages
the value of random velocity of electrons is
10^+5 m/s
the value of drift velocity is
10^-5 m/s
the angle between drift velocity and electric intensity is
180°
the formula for drift velocity is
Vd = △V/neρL
OR
Vd = I/neA
what is electric current?
the rate of flow of charge to any cross-section of wire
formula for current
I = △Q/△t
OR
I = ne/△t
unit for current
ampere = coulomb / second
how many electrons per second constitute a current of 1 ampere?
6.25 x 10^18 e
state ohms law
current flowing through a conductor is directly proportional to the potential difference applied across its ends, provided that the physical state of the conductor remains same
the proportionality constant for ohm’s law is
1/R
write formula for ohm’s law
I = 1/R x V
V= IR
formula for resistance
R = V/ I
unit for resistance
ohm = volt / ampere
resistance depends upon
resistivity (ρ)
temperature
nature
length
area
base units of ohm are
kg m2 / sec3 A2
the slope for VI graph gives
R
the area under VI graph gives
Pave
average power
the graph between V and I is
straight line originating from origin
for a graph of VI where 4 lines are originating from axis, where a is closer to x-axis and d is closer to y-axis, what is the decreasing order of resistances?
Rd > Rc > Rb > Ra
a graph is drawn between V at x-axis and I at y-axis. four straight lines are originating from origin, with line ‘a’ being close to x-axis and line d being close to y-axis, what is the decreasing order of resistances?
Ra > Rb > Rc > Rd
a VI graph is drawn, with straight lines A and B originating from origin. line A is at 30° with x-axis and line B is at 30° from y-axis. what is the ratio of resistance of A to B?
3 : 1
for series combination of resistances, what is Req?
Req = R1 + R2 + R3
for series combination of resistors, which is same: current or voltage?
current
for series combination of resistors, the Req is _________ that any individual resistances.
greater
what will be Req for series combination of resistors, if all resistances are same?
Req = nR
for parallel combination of resistor, the equivalent resistance will be
1/Req = 1/R1 + 1/R2 + 1/R3
for parallel combination of resistors, which is same, current or voltage?
voltage
the equivalent resistance for parallel combination of resistors is __________ than any individual resistance.
smaller
the equivalent resistance for parallel combination of resistors if all the resistances are equal is
Req = R/n
formulas for power
P = W/t
OR
P = VI
OR
P = I^2 R (for series)
OR
P = V^2/R (for parallel)
what is the manufacturing formula for bulb?
P = V^2/R
power is _________ proportional to area of filament
directly
what is power?
the rate of dissipation of electrical energy
the resistance of a bulb is _______ proportional to its power
inversely
1 unit of electricity is equal to how many kWh
1
power is ________ proportional to the brightness for series circuit
inversely
the bulb with highest power has ______ filament
thickest
power is _____ proportional to brightness for parallel circuit
directly
define electromotive force.
the work done on unit positive charge by the cell or battery is called electromotive force.
the terminal voltage is always ______ than emf
less
formula for emf if work and charge is given would be
emf = W/Q
the SI unit for emf is
volt
emf if terminal voltage, current and resistance is given would be
emf = V + Ir
formula for emf for closed circuit would be
emf = V + Ir
emf for open circuit is
V (terminal voltage)
formula for emf of charging circuit would be
emf = V - Ir
emf for short circuit would be
Ir
emf for closed circuit will be _______ than terminal voltage
greater
emf for open circuit will be ______ than terminal voltage
less
Power output formula is
e^2 R / (R - r)^2 + 4rR
maximum power output will be
e^2/4r
Kirchhoff’s first rule can also be written as
sum of currents flowing towards a point is equal to the sum of currents flowing away from that point
state Kirchhoff’s first rule
sum of all currents flowing in a closed loop is equal to 0
mathematical representation of Kirchhoff’s first rule
Σ I = 0
Kirchhoff’s first rule is another form of
law of conservation of energy
state Kirchhoff’s 2nd rule
sum of all potential changes in a closed loop is always equal to 0
Kirchhoff’s first rule is also known as
current rule, point rule or junction rule
mathematical form of Kirchhoff’s 2nd rule
Σ V = 0
Kirchhoff’s 2nd rule can also be written as
energy gained is equal to energy lost
Kirchhoff’s 2nd rule is also known as
voltage rule or loop rule
Kirchhoff’s 2nd rule is another form of
law of conservation of energy
resistance is ______ proportional to length
directly
resistance is ___________ proportional to area
inversely
proportionality constant for R ∝ l/A is
ρ
ρ is called
resistivity of conductor
ρ depends on
nature of conductor and temperature of conductor
what is affected by bending, compressing, stretching and cutting; resistance of resistivity?
resistance
shortcut to find resistance of a conductor if it is stretched will be
n^2 R
shortcut to find resistance of conductor if it stretched will be
R / n^2
write 3 formula for resistance
R = ρ L/A
OR
R = 4ρL/ π D^2
OR
R = ρL/π r^2
the reciprocal of resistance is called
conductance
formula for conductance is
1/R
unit of conductance is
mho, 1/ohm,
the reciprocal of resistivity will be
conductivity
formula for temperature coefficient would be
α = Rt - Rnot / Rnot △T
α is positive for
conductors
α is negative for
semi-conductors
