Ncert Exercises & Solutions

1.11) A polythene piece rubbed with wool is found to have a negative charge $3 \times 10^{- 7} C$ .

(a) Estimate the no. of electrons transferred (from which to which?)

(b) Is there a transfer of mass from wool to polythene?

(a) When polythene is rubbed against wool, the electrons are transferred from wool to polythene. The wool becomes positively charged as it loses electrons and polythene becomes negatively charged as it gains the same electorns.
Amount of charge on the polythene piece,

q = - 3 \times 10^{- 7} C

Amount of charge on an electron,

e = - 1 .6 \times 10^{- 19} C

Number of electrons transferred from wool to polythene,

n = \frac{q}{e} = \frac{- 3 \times 10^{- 7}}{- 1 .6 \times 10^{- 19}} = 1 .87 \times 10^{12}

(b)
The mass is transferred when the polythene piece is rubbed against the wool as the electron has a mass equal to

9.1 \times 10^{- 3}

kg.

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