Electricity and Magnetism | SEE Physics Notes
Definition: The flow of electrons through conductor is called Electricity.
The electricity is the flow of charge per second.
Q = 2t
or, i = Q/t = charge/ time
Father of Electricity: Michael Faraday
Types of electricity:
a) Ac (Alternating current)
b) DC (Direct current), etc.
AC (Alternating Current):
Definition: The current that change the polarity and magnitude at a certain interval of a time is called Alternating Current (AC).
It stands for the Alternating Current. Its polarity changes per second. The Ac voltages can be changed by transformer. It is generated by Dynamo. It is less dangerous then DC.
DC (Direct Current):
Definition: The current that doesn’t change the polarity and magnitude at a certain interval of a time is called Direct current (DC).
It stands for Direct current. Its polarity doesn’t changes per second. The Dc voltages can be changed by transformer. It is produced by Cell and DC Dynamo. It is more dangerous than Ac.
Effect of Current:
i. Heating effect.
ii. Lighting effect.
iii. Chemical effect.
iv. Magnetic effect, etc.
Definition: The process of converting electric energy into heat energy is known as heating effect.
When the electricity is passed through conductor the conductor is heated and it is called heating effect.
Heating element: Mostly alloys are used as heating element like as Nichrome (Nitcr) in electric press electric heater, etc.
Ni = 60%
Cr = 40%
Definition: The process of converting electric energy into light energy is known as lighting effect.
Example: Electric/ Filament bulb, and Fluorescent lamp, etc. When the electricity is passed through conductor the conductor is heated and light is emitted. It is called lighting effect.
Definition: The process of converting electric energy into chemical energy is known as chemical effect. When the electricity is passed through fused salt/ solution of salt, salt is dissociated into ions and it is called chemical effect.
ii. Electrolysis of CuSO4 solution.
iii. Electroplating, etc.
Definition: The process of converting electric energy into magnetic energy is known as magnetic effect. When electricity is passed through conductor magnetic field is produced around it is called magnetic effect.
ii. Electric bell.
iii. Telephony and Telegraphy, etc.
Definition: The lamp in which tungsten is used as light emitting element is called filament bulb.
It is oval in structure. Its life span is only 1000 hours. It converts 10% electrical energy into light and 90% in heat energy. In it, tungsten is used as light emitting element because its melting point is 3400˚c. It emits light at 200˚c.
Definition: The lamp in which fluorescent materials is used as light emitting material is called fluorescent. It is cylindrical in shape. Its life span is only 3000 hours. It converts 30% electricity and 70% into heat energy. Fluorescent materials absorbs UV (Ultraviolet) and converts into visual light.
a) Filament lamp: Oval glass bulb filled with Nitrogen or Argon because these gas don’t react with heated tungsten.
b) Tungsten filament: (Why) because its melting point is 3400˚c (High).
c) Fluorescent lamp:
Definition: The process of decomposition of acidified water into hydrogen and oxygen due to the passage of electricity is called Hydrolysis. It is also called Electrolysis of water. Water has covalent bond. It doesn’t conduct electricity in pure form. So, a pinch of salt or acid is mixed to conduct electricity (ions).
Definition: A pot in which electrolysis is conducted is called voltammeter. Water voltammeter for electrolysis of water
Definition: The deposition of anode material over cathode material by the process of electrolysis is called Electroplating.
Reaction: CuSO4 → Cu+2 + SO4-2
Hans Christian Oersted:
In 1819, He has demonstrated magnetic effect of current.
i. When current is not flowing, magnetic needle (N-S) is parallel to conductor.
ii. When current is passed through conductor, magnetic needle is deflected (N1 S1).
iii. Reason: When conductor is passed, magnetic field is produced around conductor Due to magnetic field, magnetic needle is different.
Magnetic field around current carrying:
Definition: When current is passed through conductor, magnetic field is produced around it is known as Magnetic field around current carrying.
i. We take thick cardboard and make hole at center.
ii. We pass conductor through hole of cardboard.
iii. We sprinkle iron fillings (dusts) on the card board.
iv. We pass electricity through conductor. The iron fillings make many concentric rings.
Reason: When current is passed, magnetic fields id produced around it and due to magnetic field produced, iron-filling are arranged in concentric rings.
Definition: The transformer is the electrical device, which converts high voltage into low and vice versa.
High voltage ←Transformer→ Low voltage
Components of transformer:
i. Laminated iron core.
ii. Coil (Copper wire).
iii. Transformer oil, etc.
Types of transformer:
a) Step up transformer.
b) Step down transformer, etc.
Following are the differentiate between on Step up transformer and Step down transformer:
|Step up transformer||Step down transformer|
|It converts low voltage into high voltage.||It converts high voltage into low voltage.|
|Its primary coil has less turns than secondary coil.||Its primary coil has more turns than secondary coil.|
|Use: It is used at power generation for long distance power supply.||Use: It is used in T.V, computer, and radio, etc.|
Definition: The production of induced e.m.f (Electromagnetic force potential difference) by relative motion between magnet and coil is called Electromagnetic induction.
It is demonstrated and explained by Michael Faraday (Father of Electricity). Electrical generator (Dynamo) is based on this principle.
The induced emf depends on:
a) Number of turns in coil, it more turns more induced e.m.f is produced.
b) Strength of Magnet: If magnet is more powerful more induced e.m.f is produced.
c) Relative motion: Fast than more induced e.m.f is produced, etc.
Definition: The number of magnetic lines of force passing through a surface held perpendicular to the lines of force is called magnetic flux.
It is denoted by phi (Ø). Its SI unit is Watt.
Induced e.m.f ∝ Change of flux/ time
∝ Ø/t ∝ dØ/dE
Definition: An inverter is an electrical appliance which converts AC (Alternating current) into DC (Direct current) and vice versa.
Change of battery: Inverter converts AC into Dc and battery is charged. Battery stores DC.
Definition: A fuse is a thin wire having low melting point and high resistance.
It is allow of Tin (Sn) and lead (Pb). Its melting point is low. When current or more ampere than its rated value can pass, fuse is melted and circuit is broken. Fuse contains 63% Sn and 37% Pb (Lead).
Value of fuse (I) = P.d/ Resistance
Dynamo or generator:
Definition: Dynamo or generator is a device which generates electricity on the basis of electromagnetic induction.
Definition: When current carrying conductor is placed in magnetic field, it experiences force, and it is called motor effect.
Electric motor, fans, washing machine, vacuum cleaner, etc. are based on it. These electrical devices converts electrical energy into mechanical energy.
Domestic Electrification (Wire):
a) Phase wire/ live wire: It is a red/ brown colored wire connected electrical device (load) to input current.
b) Neutral wire: It is a black or blue colored wire through which current from load returns back.
c) Earthing wire: It is yellow or green wire used to carry leakage current to the earth from device.
Definition: The electrical device which changes Ac into Dc and used to charge battery is called Charger.
Answer the following questions:
a) What is ment by one kilowatt hour in electricity?
Ans: The electricity consumed by electric load of load of one kilowatt power in one hour is known as one kilowatt hour in electricity.
b) What is meant by electric current?
Ans: The flow of electron in a conducting wire is known as electric current.
c) What is meant by electric circuit?
Ans: The pathway of electricity containing combination of source, load and switch is known as electricity circuit.
d) What is meant by electricity consumption?
Ans: The amount of electricity which id converted to the other forms of energy by using load is known as electricity consumption.
e) How is electricity consumption calcutated?
Ans: To claculate the electricity consumption the product of the number of load, power, and time is calculated:
Electricity consumption= P×N×T
f) What is meant by electric power?
Ans: The amount of electric of energy consumd by a load in one second is known as electric power.
g) Which instrument is used to measure the electrical power consumption?
Ans: Meter box is used to measure the electrical power consumption. It measures the power consumption in kilowatt hour.
h) What is meant by galvanometer?
Ans: The electrical device which is used to measure small signals of current is known as galvanometer.
i) On which principle generator and dynamo depends?
Ans: The working principle of generator and dynamo depends on the principle of electromagnetic induction.
j) What are the types of generator?
Ans: Following are the types of generator:
i. AC generator
ii. DC generator, etc.
a) The efficiency of a transformer is never 100%, why?
Ans: There is resistance in the coil of a transformer, so the efficiency of a transformer is never 100%.
b) Soft iron armature is used in electric bell, why?
Ans: The more the metal is soft the strength of magnet formed is more. So, soft iron armature is used in electric bell.
c) Filament lamp is filled with inert gases. Why?
Ans: In high temperature i.e. around 2900°C tungsten filament can get oxidised due to reaction with oxygen. So, to prevent oxidation and maintain the pressure, innert gas is filled in filament lamp.
d) Why is Nichrome used in heater?
Ans: Nichrome has high resistance and does not get oxidised even in high temperature like 900°C and can easily converts electric energy into heat energy. So, nichromee is used in heater.
e) Why should the coil of transformer be laminated?
Ans: When curent flows through the coil of transformer, eddy current is produced in the core. If the coil of transformer becomes a single piece, the amount of eddy current increases and the transformer gets heated and damaged. Output is also low. So, the coil of transformer is laminated.
a) Phase wire and Neutral wire
Ans: Following are the differentiate between on phase and neutral wire:
|Phase wire||Neutral wire|
|It is a red/ brown colored wire connected electrical device (load) to input current.||It is a black or blue colored wire through which current from load returns back.|
|We feel electric on touching it.||We feel electric on touching it.|
i. Power consumption (pc): Power (P) × Hour(H)
=Watt × Hours
ii. Watt = Volt × Amper
Power = Volt (V) × current (Amper)
According to ohm’s law:
V = IR
PD = Current × Resistance
Volt Amper ohm (Ω)
a) An electric kettle rated 220 V and 2.2 KW works for 3 hours. Find the energy consumption and current drawn by it.
PD = 220 volt
Power= 2.2 kw
Time = 3 hours
We know that,
Power consumption= power × hour
= 2.2kw × 3 hour
= 6.6 Unit
Again, current drawn (I)= ?
∴ I = P/V = 2.2 × 100W/ 220 = 2200/220
∴The energy consumption is 6.6 unit and current drawn by it is 10 AMP.
b) If a 1000W heater is to be operated at a 220V mains, what must be the rating of the force to be used in the circuit?
P = 1000 W
Fuse (I)= ?
We know that,
∴I = P/V= 1000/220
=50/11 = 4.5 = 5AMP
∴So the 5AMP is the rating of the force to be used in the circuit.
c) If thw irons of 750W each are used 8hours a month. How much tariff should be paid? Cost of one unit of electricity is Rs 7.
N= 8 hours
We know that,
Power consumption= 750 × 8 × 2
= 2 × 750 × 8/ 1000
= 12 KHW
∴ The cost of 1 unit= Rs. 7.00
∴The cost of 12 unit = 12×7 = Rs. 84.00
d) What type of combination of cells is shown in the given circuit? Calculate the power of the bulb if 0.2Acurrent flows through the curcuit.
Volt = 6
We know that,
Watt= Volt × Amp
e) In a transformer, the number of turns in primary coil is 100. If the primary and secondary voltage are 220V and 110V respecctively, calculate the no of turns in the secondary coil.
Vp= 220 volt
Vs= 110 volt
we know that,