We all know that atom is electrically neutral. Atom consist of positive Core and electron revolve around that positive Core called nucleus. Number of protons in the nucleus is always equal to number of electrons revolving around that nucleus, hence the total charge on atom is zero.
When we separate the electron from the nucleus then the parent atom becomes positive and electrons become negative.
Positive charge- when we separate the electrons from the atom then atom becomes positive, simply deficiency of electron is called positive charge.
Negative charge: if the body has excess number of electrons in it then we say that, the body has negative charge.
SI unit of charge is coulomb.
Electric current: In solid material electron is responsible for flow of current.
Charge Carrier responsibile for flow of current.
- In solid conductor: Electrons are responsible for flow of current. But in some cases deficiency of electronic means hole, that hole is responsible for flow of current insemiconductor devices.
- In Liquid: Both positive and negative ions are responsible for flow of current. As we studied ionisation, when we add Nacl in water then current will flow in that.
- In gases: the current flow in gases is due to both ions.
At room temperature, the temperature is about 300 K, then energy associated with that temperature is enough for free the electron.The electrons absorb energy and get separated from its parent nuclei. This free electron is responsible for flow of current.
Definition of current: Rate of flow of charge per unit area per unit time is called current.
I = q / t
Where
I current
q = charge
t = time
The SI unit of current is ampere. Andre Marie Ampere is famous physicist so in memory of that physicist we use ampere is the unit of current.
One ampere- if one coulomb of charge flow through unit cross sectional area in unit time, that current is called as one ampere.
1 Ampere = 1 C coulomb / 1 second
1 coulomb = no of electrons × charge on electron.
No of electrons = 1 coulomb / charge on electron
As charge on electron is 1.6 × 10⁻¹⁹ C. Put this value in above then we get,
No of electrons = 1/ 1.6 × 10⁻¹⁹
No of electrons = 6.25 × 10¹⁸
There are approximately 6.25 × 10¹⁸ electrons in one coulomb.
More about Ampere.
- Ampere is basic or fundamental unit like meter, second, kilogram etc.
- We also use milliampere, microampere unis for measuring current.
- We can measure current using ammeter.
1 milliampere = 10⁻³ A
1 microampere = 10 ⁻⁶ A
Q) Define one ampere
Q) how many electrons are needed for 2 coulomb of charge.
Q) Give SI unit of current.
Q) Define current.