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.
Answers
Answer:
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Question 11
A polythene piece rubbed with wool is found to have a negative charge of 3 × 10−7 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
n can be calculated using the relation, q = ne
n equals q over e
=fraction numerator minus 3 x 10 to the power of minus 7 end exponent over denominator minus 1.6 x 10 to the power of minus 19 end exponent end fraction
= 1.87 × 1012
Therefore, the number of electrons transferred from wool to polythene is 1.87 × 1012.
(b) Yes. There is a transfer of mass occur. This is because an electron has mass,
as we know
me = 9.1 × 10−3 kg
Total mass transferred from wool to polythene,
m = me × n
= 9.1 × 10−31 × 1.85 × 1012
= 1.706 × 10−18 kg
Hence, a negligible amount of mass is transferred from wool to polythene.