its a nice project on electricity chapter

2. • There are two types of charges :-
• Positive charge :- These are made of sub atomic particle
proton.
• Negative charge :- These are made of negative sub atomic
particle electron.

26. • When two (or more) resistors are connected between the same
points, they are said to be connected in parallel.
• According to the law of combination of resistance in parallel:
The reciprocal of the combined resistance of any number of
resistances connected in parallel is equal to the sum of the
reciprocals of the individual resistances.
1/R= 1/R1 +1/R2 +1/R3+………..
• When a number of resistances are connected in parallel then
their combined resistance is less than the smallest individual
resistance.

27. • When a number of resistance are connected in parallel, then the
potential difference across each resistance is same which is
equal to the voltage of battery applied.
• When a number of resistances connected in parallel are joined to
the two terminals of a battery, then different amounts of current
flow through each resistance (which depend on the value of
resistance). But the current flowing through each parallel
resistance, taken together, is equal to the current flowing in the
circuit as a whole. Thus, when a number of resistance are
connected in parallel, then the sum of current flowing through all
the resistances is equal to the total current flowing in the circuit.

29. • If one electric appliance stops working
due to some defect, then all other
appliances keep working normally.
• In parallel circuits, each electric
appliance has its own switch due to which
it can be turned on or off independently.
• Each appliance gets same voltage as that
of power source.
• Overall resistance of household circuit is
reduced due to which the current from
power supply is high.
• If one electric appliance stop working due
to some defect, then all other appliances
stop working.
• All the electric appliances have only one
switch due to which they cannot be turned
on or off separately.
• In series circuit, the appliances do not get
same voltage (220 V) as that of the power
supply line.
• In series circuit the overall resistance of
the circuit increases due to which the
current from the power source is low.

33. • The heat produced in wire is directly
proportional to
i. Square of current.
ii. Resistance of wire.
iii.Time for which current is passed.

34. There are many practical uses of heating effect of current. Some of the most common are as follows.
• An incandescent light bulb glows when the filament is heated by heating effect of current, so hot
that it glows white with thermal radiation (also called blackbody radiation).
• Electric stoves and other electric heaters usually work by heating effect of current.
• Soldering irons and cartridge heaters are very often heated by heating effect of current.
• Electric fuses rely on the fact that if enough current flows, enough heat will be generated to melt
the fuse wire.
• Electronic cigarettes usually work by heating effect of current, vaporizing propylene glycol and
vegetable glycerin.
• Thermistors and resistance thermometers are resistors whose resistance changes when the
temperature changes. These are sometimes used in conjunction with heating effect of current(also
called self-heating in this context): If a large current is running through the nonlinear resistor, the
resistor's temperature rises and therefore its resistance changes. Therefore, these components can
be used in a circuit-protection role similar to fuses, or for feedback in circuits, or for many other
purposes. In general, self-heating can turn a resistor into a nonlinear and hysteretic circuit
element.

35. • H = I2 Rt gives the rate at which electric energy is dissipated or consumed in an electric
circuit. This is also termed as electric power. The power P is given by
P = VI
Or P = I2R = V2/R
• The SI unit of electric power is watt (W). It is the power consumed by a device that carries 1 A
of current when operated at a potential difference of 1 V. Thus,
1 W = 1 volt × 1 ampere = 1 V A
• The unit ‘watt’ is very small. Therefore, in actual practice we use a much larger unit called
‘kilowatt’. It is equal to 1000 watts. Since electrical energy is the product of power and time,
the unit of electric energy is, therefore, watt hour (W h). One watt hour is the energy consumed
when 1 watt of power is used for 1 hour. The commercial unit of electric energy is kilowatt
hour (kW h), commonly known as ‘unit’.
1 kW h = 1000 watt × 3600 second
= 3.6 × 106 watt second
= 3.6 × 106 joule (J)