Electricity in Physics

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Electricity in Physics

Electron has a negative charge equal to -1.6 x 10-19 coulomb while the charge on a proton is exactly equal and opposite to that on electron and is equal to +1.6 x 10-19 coulomb.

Charge can neither be created nor destroyed. This is known as law of charge conservation; charge conservation is followed in nuclear reactors, electricity, electrification by friction, electrification by induction, etc.

For the electrification of a body only electrons are responsible.

If a body is negatively charged then it has an excess of electrons, while if a body is positively charged then it has a deficit of electrons.

Good conductors are the substances which allow an easy flow of charge through them.

They have a large number of free e- in them. Best conductor of electricity is Ag. All metals are good conductors.

If a small charged conductor is placed inside another big and hollow charged conductor and the two are joined by a wire then the charge flows from smaller conductor to bigger conductor because the potential of smaller conductor is more than that of bigger conductor.

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Fuse Wire

Fuse Wire is used in a circuit to control the maximum current flowing in a circuit. It is a thin wire having high resistance and is made up of a material with low melting point.

House Wiring circuits are in parallel therefore the voltage across each bulb is constant.

The filament of 60 W bulb is thinner than the filament of 100 W bulb.

If two bulbs, one of 60 W and the other of 100 W are connected in parallel, then 100 W bulb will glow more.

If two bulbs, one of 60 W and other of 100 W are connected in series, then the 60 W bulb will glow more, because in series combination current through both the bulbs is the same and the Power consumed P = I²R or P ∞ R.

Now, since the resistance of 60 W bulb is more than the resistance of 100 bulb, the 60 W bulb will glow more.

In Series Resistance Circuit, it should be remembered that :

  • The current is same in every part of the series circuit.
  • The total resistance in the circuit is the sum of the individual resistances including internal resistance of the cell (if any).
  • Voltage across any part of a circuit is proportional to the resistance of that part
  • Current in the circuit is independent of the relative positions of the various resistances in the series.

In Parallel Combination of Resistances, it should be remembered that :

  • Total current through the combination is the sum of individual currents through the various branches
  • The potential difference across all the resistances is the same.
  • The current through each branch is inversely proportional to die resistance of that branch.
  • The reciprocal of the total resistance of the combination is equal to the sum of the reciprocals of the individual resistances.
  • Resistivity of a conductor changes with impurity. The impurity increases the resistivity.
  • Resistivity of an alloy is greater than the resistivity of its constituents.
  • Resistivity increases with temperature.

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