Electricity | 8 Flashcards
Types of electricity
Static and Current
Static electricity
Observed in insulators (Rubber , foam , cloth)
Current electricity
Observed in conductors (Metals , circuits)
What happens when you rub 2 insulators together
Due to friction , electrons jump from one object to another
The material that gains electrons gets a –ve
charge.
The material that loses electrons is left with atoms
with more protons, meaning a positive charge
This charge collected is referred to as STATIC
charge, as it stays in the materials.
This process is called – charging by friction
Properties of static charges
In charging by friction, both the objects get
static charges – one negative and one positive.
The amount of negative charge is equal to the amount of positive charge (as the no: electrons gained by one object is equal to the no: of electrons lost by positive object)
Opposite (unlike) charges attract, like charges repel.
Earthing
Static charges have a tendency to neutralize
themselves, when there is a path to a
conducting object.
Charging by induction
If there is a positively charged glass rod
(which is charged by friction).
Now we bring it close to an uncharged (neutral object),
in this case a sphere (kept on an insulated base)
When we bring the rod close, the electrons in the sphere
will be attracted towards the positively charged rod, as
opposite charges attract.
So, the electrons move to the left, leaving atoms with
excess protons on the right.
This causes the sphere to have negative charge in the
left, and positive charge in the right.
This is called Charge separation, and the process is
called Charging by Induction.
Charge
Coulombs
Refers to the negative charge carried by the
electrons
1C = Charge of 6 x 10 18 electrons
Voltage
It is the amount of energy given to each
coulomb of charge.
Also called Potential difference OR P.D,
since the electrons are pushed due to the
energy difference between 2 terminals.
Voltage = Energy / Charge
1V = 1J of energy to each coulomb of
charge
6V = 6J of energy to each coulomb of
charge
Electro - motive force
It is the maximum voltage from a cell, when it is not part of a complete circuit.
Current
The amount of charge that flows in one
second is called CURRENT
Symbol = ‘I’
Current (I) = amount of charge
—————————-
Time
Amphere - Ammeter measures
Resistor
It is a component that opposes the flow of electrons in a circuit.
It is made by winding wires from alloys like
Nichrome, Constantan etc.
Because resistors oppose the flow of electrons, they reduce the current in the circuit.
The amount of opposition a resistor offers is called RESISTANCE. It is measured in Ohms.
What energy transfer takes place in a resistor?
Electrical to heat energy
Factors affecting resistance of a piece of wire:
Length of wire ( As length l increases,
resistance R increases)
Cross-sectional area or thickness (As cross
sectional area A increases, resistance R
decreases)
Temperature of wire (As temperature
increases, R increases)
Material
Comparing resistivity with 2 resistors of same material
R1 x A1 R2 X A2
———– = ————-
L1 L1
