electricity Flashcards
properties of charge
- charge is of two types +ve, -ve
- like charges repel, unlike charges attract
electric/electrostatic field
force per unit charge experienced by a small charge
magnitude of charge decides how big its electric field is
quantization of charge
net charge on a body is always an integral multiple of elementary charge
Q=±ne
elementary charge = least amount of charge that can be present on a stable body (cahrge on elcetron = 1.6*10^-19C)
law of conservation of charge
charge can neither be created nor destroyed it can only be transferred from one body to another
charge transfer mechanisms
friction
free/delocalised electrons gain/absorb heat energy from friction and gain energy which they use to eject themselves to a different body.
why sometimes despite rubbing a body, the object does not get charged?
- no free electrons present
- friction does not provide enough energy for the electrons to eject themselves
conductor
substances which allow electric charges to flow through them
charges reside on the surface of a conductor
metals are best conducted because they have large number of free electrons
fuse
thin piece of wire that melts when a certain amount of current flows through it, breaking the circuit
better option is circuit breakers that dont get permanantly damaged after 1 use but they are more expensive
conduction
process of charging an object by bringing it in contact with the other
induction
process of charging an object without bringing it in physical contact with the other (just by bringing it near another cahrged object)
potential difference
work done per unit +ve charge in moving a small charge from one point to another within the electric field
- charge flows due to potential difference like air flows due to pressure difference
charge flows until potential difference = 0
current
- rate of flow of charge
- amount of charge flowing per unit time
I=Q/t
1A current?
if the force per unit length b/w two parallel current carrying wires carrying the same amt. of current seperated by 1m distance in air in vacum is 2*10^-7 Nm^-1, then the curent flowing through each wire is said to be 1A.
ohm’s law
for all external conditions such as temperature remaining constant, the current flowing through the two ends of a wire is directly proportional to the potential difference applied across the two ends
I∝V
V=IR
y=xm+c
ohmic conductor
conductors which obey ohm’s law
non-ohmic conductor
conductors which do not obey ohm’s law
resistance
property of material because of which it opposes/restricts the free flow of charge
factors affecting resistance
- length
- cross-sectional area
- material of the wire
- temperature
R∝l/A
R=rho*l/A
rho=resistivity - based on 1. nature of material 2. temp
more temp might cause more resistance due to more collisions
more temp might cause less ressitance because more electrons absorb energy and get ejected
resistivity?
resistance offered by a wire of unit length of unit cross-sectional area
when are two or more resistors said to be in series
if the same amount of current flows through all of the resistors
series combination of resistors
- current flowing through all the resistors in a series combination is the same
- net potential drop across all the resistors = sum of potential drops across individual resistors
- the net resistance of a series combination = sum of individual resistors
- net resistance > any of the resistors in the combination
I1=I2=I3
V1+V2+V3=Vs
R1+R2+R3=Rs
when are two or more resistors said to be in parallel
if current has multiple paths to travel in
parallel combination of resistors
- potential drop across all resistors is the same
- net current flowing through the comination = sum of current flowing through individual resistors
- reciprocal of net resistance = sum of the reciprocals of individual resistors of the combination
- net resistance < any of the resistors in the combination
V=V1=V2=V3
I=I1+I2+I3
1/Rp = 1/R1+1/R2+1/R3
power
rate at which work is done or energy is consumed
P=W/t
P=Q/t
P=VI
P=I^2R
P=V^2/R
