Cbse class 10th electricity
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Transcript of Cbse class 10th electricity
ELECRICITY
Def. of Electricity Electric Current Electric Potential & Potential Difference Electromotive Force (emf) Electric Circuit and components Current and Voltage Measurements OHM’s Law Factors Affecting Resistance Combination of Resistors(Series & Parallel) Heating Effect of Electricity and its apps.
NOTE-Direction of CONVENTIONAL Current is opposite to direction of flow of electrons.
Contents
Electricity is a form of a energy that can be easily changed to
many other forms
What is Electricity ?
Electric Current is the flow of electric charge Measured as the rate of flow of electric
charge Denoted by I
I=Q/t SI unit -> Amperes(A)
NOTE-Direction of CONVENTIONAL Current is opposite to direction of flow of electrons.
What is Electric Current ?
Electric Potential - Work done in moving a unit charge from infinity to a point
.∞ A . Potential Difference – The difference between
potential at two points
. ∞
B. A.
Electric Potential & Potential Difference
Potential difference
POTENTIAL DIFFERENCE = Work Done (W)/Charge(Q)
V=W/Q
SI Unit => VOLTS
Electromotive Force (e.m.f)
Electromotive force is the same as voltage.
E.m.f refers to the amount of energy supplied by the electric source (eg. battery) to each unit of electric charge
E.m.f is also measured by a voltmeter
Electromotive Force (e.m.f)
Potential Difference
How does an Electrical Appliance Work?
To make an electrical appliance work, electricity must flow through it.
The path along which the electric current moves is called the electric circuit.
An Electric Circuit is an electrical device that provides a path for electricity to
flow.
Electric Circuit
Circuit diagrams for open and closed circuits
Open circuit. Bulb does not light up when the switch is open.
Close circuit. Bulb will light up when the switch is closed.
Symbols
Ammeter It must be connected in series in the
circuit.
Positive side of ammeter must be connected nearest to the positive terminal of the battery (electric cell), and vice versa.
VoltmeterVoltmeters must be connected in
parallel to the circuit.The positive side of voltmeter is
connected to the positive terminal of
the cell, and vice versa.
At constant temperature, Current flowing through a conductor is directly proportional to
potential difference across its ends
V∝I
V/I = Constant = R
V=IR R -> Ressiatance(Ω or ohm)
OHM’s Law
Fixed Resistors and Variable Resistors
Fixed resistors have only one resistance value
Variable resistors can be adjusted to change the resistance, example- Rheostat
Fixed Resistors Rheostat
Length of Conductor ->> R∝l Cross-sectional Area of conductor ->> R ∝ 1/A
Nature of material of conductor Temperature of conductor
R∝l/A
ρ – Constant of proportionality called ResistivityUnit of Resistivity – ΩmMetals and Alloys have very low resistivity whereas insulators
have very high resistivity
Factors Affecting ‘R’
R= ρl/A
Resistance of a system of Resistors
There are 2 ways of joining resistors together
1.Series2.Parallel
Series Circuit
Rs = R1 +R2 + R3
Parallel Circuit
1/Rp = 1/R1 + 1/R2 + 1/R3
Heating Effect of Electric CurrentWhen an electric current flows through a wire, the wire heats up. Electrical energy has been converted into heat energy.
The greater the resistance of the wire, the greater the amount of heat produced. This heating effect is used in common electrical appliances.
Iron Kettle
The work done in moving the charge Q through a potential difference V is VQ
Therefore, the source must supply energy equal to VQ in time t.
So, power input to the circuit by the source is
P = V(Q/t)
P=VIEnergy supplied to the circuit by the source in time t is
P × t
orH= VIt H=I²Rt
filament wire produces heat and light
In a light bulb, the heated filament which is also a resistance wire, becomes so hot that light is also emitted.
A kettle uses both copper and nichrome wires.Copper has low resistance while nichrome has high resistance.
Which material, copper or nichrome, should be used for the heating element, and for the external wire?
Use copper wire for the external wire as it has low resistance & produces less heat
Use nichrome wire for the heating element as it has high resistance& produces a lot of heat
THANK YOU