Question

A polythene piece rubbed with wool is found to have a negative charge of 6.4×10^-14 C . Find the
a) no of electrons transferred
b) mass gained by the polythene.

Answer 1

$\color{darkblue}\underline{\underline{\sf Given-}}$

• Polythene piece rubbed with wool found to have a charge of (Q) = ${\sf 6.4×10^{-14}C}$

$\color{darkblue}\underline{\underline{\sf To \: Find-}}$

• No. of electrons transferred
• Mass gained by the polythene.

$\color{darkblue}\underline{\underline{\sf Solution-}}$

✏ No. of electron transferred (n)

★$\underline{\sf Formula \: Used-}$

$\large\color{violet}\bullet\underline{\boxed{\sf Q=ne}}$

${\sf Charge\: on \: one \:electron (e) = 1.6×10^{-19}C}$

$\implies{\sf n =\dfrac{Q}{e}}$

$\implies{\sf n=\dfrac{6.4×10^{-14}}{1.6×10^{-19}}}$

$\color{red}\implies{\sf n=4×10^5 }$

★Number of electrons is $\underline\color{red}{\sf 4×10^5}$

✏ Mass gained by polythene

★$\underline{\sf Formula \: Used-}$

$\color{violet}\bullet\underline{\boxed{\sf Mass \: gained =n×mass \: of \: one \: electron }}$

$\implies{\sf 4×10^5×9.1×10^{-31} }$

$\color{red}\implies{\sf 36.4×10^{-26}kg }$

★Mass gained by polythene is $\underline\color{red}{\sf 36.4×10^{-26}kg}$

Answer 2

$\mathtt{\huge{ \fbox{Solution :)}}}$

Given ,

• Charge (q) = 6.4 × (10)^-14

We know that ,

The charge on a body is an integral multiple of electrons

$\large \mathtt{ \fbox{Charge \: (q) = ne}}$

Thus ,

6.4 × (10)^-14 = n × 1.6 × (10)^-19

n = 4 × (10)^5

Hence , the number of electrons transferred is 4 × (10)^5

Now , we have to find the mass gained by the polythene

Thus ,

$\mathtt{ \large \fbox{M = mass \: of \: electrons × no. \: of \: electrons}}$

m = 9.1 × (10)^-31 × 4 × (10)^5

m = 36.4 × (10)^-26 kg

Hence , the mass gained by the polythene is 36.4 × (10)^-26 kg

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