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# 1. Fill in the blanks(i) 1mC = ____ C(ii) 1 micro C = ___ C (iii) 1 C = ____ electrons(iv) 5 C = ____ electrons(v) When current flows in a circuit______ energy changes to______energy.2. A polythene piece rubbed with wool is found to have negative charge of $3.2 \times {10^{ - 7}}{\rm{C}}$.Estimate the number of electrons transferred from wool to polythene. Verified
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Hint: When matter is put under an electromagnetic field, it acquires an electric charge, which allows it to undergo a force. Positive and negative charges are the two forms of electric charge (commonly carried by protons and electrons respectively). The charge of the proton is $+e$, and the charge of the electron is $e$.

A basic physical property that allows objects to experience an enticing or repulsive force against one another is electric current, or charge for short. The coulomb is the fundamental unit of charge (C). Positive charge (exhibited by protons) and negative charge (exhibited by electrons) are the two forms of charge (exhibited by electrons). Coulomb's law defines the electric forces between charged particles; the electromagnetic force becomes more complex as the charges pass.

The coulomb is the SI unit for electric charge. It is often abbreviated as 'C'. A coulomb is the amount of charge generated by a one-ampere current flowing for one second.
(i) 1mC = ____ C
As in mm , 1000 mm = 1m
Here too, 1000 mC = 1 C
Vice versa, $1mC = {10^{ - 3}}C$

(ii) 1 micro C = ___ C
As in mm , 1000000 micro C = 1m
Here too, 1000000 microC = 1 C
Vice versa, $1\,micro\,C = {10^{ - 6}}C$
The charge on $6.25{\rm{ }} \times {\rm{ }}{10^{18}}$electrons is equivalent to one coulomb.

(iii) $1 C = 6.25{\rm{ }} \times {\rm{ }}{10^{18}}$electrons
(iv) $5 C = 5 \times 6.25{\rm{ }} \times {\rm{ }}{10^{18}}$
$\Rightarrow 5 C= 31.25{\rm{ }} \times {\rm{ }}{10^{18}}$ electrons

(v) As electrons pass through a conductor, such as a metal wire, an electric current flows. The ions in the metal will interfere with the travelling electrons. When the resistance in a circuit is raised, such as by adding additional electrical elements, the current decreases.When current flows in a circuit mechanical energy changes to electrical energy.

$2.$ Since $Q = 3 \times {10^{ - 7}}C$
$\Rightarrow e = 1.6 \times {10^{ - 19}}\,C$
Since
$Q = {\rm{ ne }},n = \dfrac{Q}{e}$
Substituting the values
$n = \dfrac{Q}{e} \\ \Rightarrow n= \dfrac{{3 \times {{10}^{ - 7}}C}}{{1.6 \times {{10}^{ - 19}}C}} \\ \therefore n= 1.875 \times {10^{12}}$
Number of electrons transferred is $1.875 \times {10^{12}}$.

Note: The electron is a subatomic particle with the symbol e or and a minus one elementary charge electric charge. Electrons are the first generation of the lepton particle family, and since they have no recognised components or substructure, they are considered elementary particles.