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# TNPSC Free Notes Physics In English – Electricity

இந்தக் கட்டுரையில், TNPSC குரூப் 1, குரூப் 2, குரூப் 2A, குரூப் 4 மாநிலப் போட்டித் தேர்வுகளான TNUSRB, TRB, TET, TNEB போன்றவற்றுக்கான  முறைகள் இலவசக் குறிப்புகளைப் பெறுவீர்கள்.தேர்வுக்கு தயாராவோர் இங்குள்ள பாடக்குறிப்புகளை படித்து பயன்பெற வாழ்த்துகிறோம்.

### Electricity:

Ohms law:
 At a constant temperature, the steady current ‘I’ flowing through a conductor is directly
proportional to the potential difference ‘V’ between the two ends of the conductor.
 V = I R
 Not a Universal law
 Not for Semiconductor

Electric Potential difference (V):
 Unit – Volt
 Symbol – V
 Quantity – Scalar
 Measuring Device
 Voltmeter(closed circuit)

Potentiometer:
 EMF (Open Circuit)
 Voltage (Closed Circuit)
 Voltage Stabilizer (to constant the voltage – Zener diode)
Transformer:
 Step up
 Step down
 Principle – Mutual Induction

Step up
Transformer

Step down
Transformer
Voltage V P &lt; V S V P &gt; V S
Current I P &gt; I S I P &lt; I S
Number of turns N P &lt; N S N P &gt; N S
Transformer
ratio

K= V S / V P = N S / N P = I P / I S
K &gt; 1 K &lt; 1

Electric current:
 Fundamental quantity
 Flow of charge
 Quantity – Scalar

 Unit- ampere (c/s)
 Measuring device
o Galvanometer(small)
o Ammeter
Types of current:
 Alternating current:
o Sinusoidal wave
o F = 50Hz (India)/60Hz (USA)
o V = 220V (India)/110V (USA)
o T = 0.02sec
o Induction(henry)
 Direct current:
o constant current
o Frequency = Zero
o Time period=Infinity
Charge carriers:
 Conductors – electrons
 Semiconductors – Holes and electrons
 Electrolyte – Ions (cations and anions)
Electric Charge:
 Attraction or Repulsion
 Unit – coulomb
 Quantity – Scalar
 Measuring device – Electroscope
 1F = 96500 coulomb = 96500 x 6.253×10 18 electrons
Basic units of charge:
 Electric charge = ±1.6 x10 –19 C.
 1coulomb = 1/(1.6 x 10 -19 ) = 6.253×10 18 electrons
Electric field:
 The lines representing the electric field are called ‘electric lines of force.
 The electric lines of force are straight or curved paths along which a unit positive charge
tends to move in the electric field.

Resistance and conductance:
Resistivity and Conductivity:
 Resistance is directly proportional to length of the conductor and inversely proportional
to the cross section area of the conductor.
 R = ρ (L/A)
 L = length of the conductor
 A = area of cross section.
 ρ = resistivity
 Unit – ohm metre
 Conductance = reciprocal of its resistance (R).
 Unit = mho or ohm – 1
 The conductivity is reciprocal of electrical resistivity of a material.
 Unit – is ohm – 1 metre – 1
Resistance in series and Parallel:
 Current constant
 Voltage differs
 R TOTAL = R 1 + R 2 + R 3
 R TOTAL &gt; R MAX
 Galvanometer and Ammeter
 Fuse wire connect in series

Resistances in parallel:

 Voltage constant
 Current varies
 Voltmeter and potentiometer
 1/R TOTAL = 1/R 1 +1/R 2 +1/R 3 …1/R n
 R TOTAL &lt; R MIN

Effects of Electric Current:
 Heating effect
 Magnetic effect (Magnetism)
 Chemical effect
Heating effect of current:
 Discovered by joule.so it is called as jolu’s law of heating
 H = I 2 RT
 H = Amount of heat produced
 I = Current
 R = Resistance
 T = Time
Wires:
 Red wire – live wire
 Black wire – neutral
 Green wire – earthing
Nichrome – nickel + chromium
 High melting point
 High resistivity (1.5X10 – 6 Ω m)
Bulb filament – tungsten
 High melting point
 High Resistivity

Fuse wire – lead + tin
 Low melting point
 High Resistivity
Chemical effect of current:
 Cells-used to create potential difference in the circuit.
 Primary cells – non reachargable
 Secondary cells – rechargeable

Electric Power:
 P = 1 volt x 1 ampere = 1 watt
 1 kWh = 1000 watt hour = 1000 (60 60) watt second = 3.6 10 6 J
Horse Power:
 The horse power is a unit in the foot – pound – second (fps) or English system, sometimes
used to express the electric power. It is equal to 746 watt.

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