1.

A polythene piece rubbed will wool is found to have a negative charge of `3.0xx10^(-7)C`. (a) Estimate the number of electrons transferred (from which to which )? (b) Is there a transfer of mass from wool to polythene?

Answer» (a) When polythene is rubbed against wool, a number of electrons get transferred from wool to polythene. Hence, wool becomes positively charged and polythene becomes negatively charged.
Amount of charge on the polythene piece, `q = −3 × 10^(−7) C`
Amount of charge on an electron, `e = −1.6 × 10^(−19) C`
Number of electrons transferred from wool to polythene = n can be calculated using the relation,
q = ne
`n=(q)/(e)`
` =(-3 xx 10^(-7))/(-1.6 xx 10 ^(-19))`
`= 1.87 xx 10^(12)`
Therefore, the number of electrons transferred from wool to polythene is `1.87 × 10^(12)`.
(b) Yes
There is a transfer of mass taking place. This is because an electron has mass,
`me = 9.1 × 10^(−3) kg`
Total mass transferred to polythene from wool,
`m = m_(e) xx n`
`= 9.1 xx 10 ^(-31) xx 1.85 xx 10^(12)`
`= 1.706 xx 10^(-31) xx 10^(-18) kg`
Hence, a negligible amount of mass is transferred from wool to polythene.


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