The number of electrons present in 1C of charge is
By quantisation of charge, q = ne
or
A cup contains 250 g of water. Find the total positive charges present in the cup of water.
Mass of water = 250 g,
Molecular mass of water = 18 g
Number of molecules in 18 g of water = 6.02 x 10^{23}
Number of molecules in one cup of water = (250/18) x 6.02 x 10^{23}
Each molecule of water contains two hydrogen atoms and one oxygen atom, i.e., 10 electrons and 10 protons.
∴ Total positive charge present in one cup of water
= (250/18) x 6.02 x 10^{23} x 10 x 1.6 x 10^{19 }C = 1.34 x 10^{7}C.
A polythene piece rubbed with wool is found to have a negative charge of 6 x 10^{7} C. The number of electrons transferred to polythene from wool is
Here, q = 6 x 10^{7} C
∴ Number of electrons transferred from wool to polythene, n =
If 10^{9} electrons move out of a body to another body every second, then the time required to get charge of 1 C on the other body is
The charge given out in one second = 1.6 x 10^{19} C x 10^{9} = 1.6 x 10^{10}C
Time required to accumulate a charge of 1 C
= 1/(1.6 x 10^{10}) = 6.25 x 10^{9} s = 198 years
The number of electrons that must be removed from an electrically neutral silver dollar to give it a charge of +2.4 C is
Total charge, q = 2.4 C
Then by quantization of charge, q = ne
∴ number of electrons, n = q/e = 2.4C/1.6 x 10^{19} C = 1.5 x 10^{19}
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