Search for notes by fellow students, in your own course and all over the country.
Browse our notes for titles which look like what you need, you can preview any of the notes via a sample of the contents. After you're happy these are the notes you're after simply pop them into your shopping cart.
Document Preview
Extracts from the notes are below, to see the PDF you'll receive please use the links above
Chapter 12 - Electricity
Introduction
Electricity originated from the Greek words “Electrica” and “Elektron”
...
Gilbert classified these materials as Vitreous and Resinous
...
Frictional Electricity
Fur, Flannel, Wax, Glass, Cotton, Paper, Silk, Human skin, Wood, Metals, Rubber, Resin,
Amber, Sulphur, Ebonite
...
Fundamental Laws of Electrostatics
There are two kinds of charges- positive and negative
...
Coulomb’s Law
F α (q1q2)/r2
The electrostatic force of attraction or repulsion between a pair of charges is directly
proportional to the product of the charges and inversely proportional to the square of the
distance between them
...
For similar charges the force is repulsive and for dissimilar charges it is attractive
...
This means electrons have moved from fur to ebonite
...
So charges are neither created nor destroyed but transferred
from one material to the other
...
Conductors allow free flow of charges
...
If q is the charge in coulomb and t is the time is seconds then current I=q/t
The SI unit of current is ampere (A)
...
Symbols used in electric circuit
Electric
Component
Function/Description
A connecting wire is represented by a straight
line
...
The resistor is represented by a zip zap line
...
The resistor wire is
generally made from alloys, such as nichrome,
manganin, constantan and eureka
...
Source of electrical
current
...
Here the
cells are arranged in series
...
An electric device, such as incandescent lamp, is
lamp, glow lamp, or fluorescent lamp that emits
light when voltage is applied across the
terminals
...
Symbol
A diagram which shows how different components in a circuit have been connected using
conventional symbols for the components is called a circuit diagram
...
If W is the work done q is the charge, then electric potential V = W/q
The SI unit of electric potential is Volts (V)
Electric Potential Difference
The electric potential difference between two points is the work done in carrying a unit positive
charge from one point to the other
...
This work done is stored in the form of potential energy of the charges
...
IV
V = I × R, where R is the resistance offered
...
The SI unit of resistance is OHM (Ω)
1 ohm is the resistance offered by a wire carrying 1 A current when 1 V is applied across its ends
...
The SI unit of resistivity is ohm-meter (Ω − m)
...
Reciprocal of resistivity is called conductivity
...
SI unit of conductivity is ohm-1 m -1 or mho-m-1
Effect of Temperature
The resistivity of a conductor increases linearly with increase in temperature
...
The resistivity of a semiconductor decreases with increase in temperature
...
Semiconductors and Superconductors
Materials having resistivity between that of an insulator and a conductor are called
semiconductors
...
Resistances in Series
If resistances R1, R2 and R3 are connected in series the equivalent resistance R s = R1 + R2 + R3
Resistances in Parallel
1
If resistances R1, R2 and R3 are connected in parallel the equivalent resistance Rp is given by R =
p
(1/R1) + (1/R2) + (1/R3)
Electrical Energy
Because of the existence of resistance to the flow of current work has to be done in order to
maintain the flow of current
...
SI unit of electrical energy is Joule
...
H = I2Rt, this is Joule’s law of heating
...
Power = work done/time
...
Calculation of Power for House Hold Electricity
Kilowatt hour (kWh) is the commercial unit for electrical energy
1 kWh = 3
...
of units of electricity consumed in a household = no