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When 10²⁰ electrons are removed from a neutral metal plate through some process, the charge on it becomes ______.

Asked in GSEB Board March 2018 · Properties of charge

• (1) -1.6 C
• (2) +1.6 C
• (3) +16 C
• (4) 10⁻¹⁹ C

Step-by-step solution

Why the other options are wrong

• (1) Two things go wrong at once here: the sign, since taking electrons away leaves the plate short of negative charge and so positive, and the size, since 10²⁰×1.6×10⁻¹⁹ = 16 C, ten times this.
• (2) This is the answer for 10¹⁹ electrons: 10¹⁹×1.6×10⁻¹⁹ = 1.6 C. Here ten times as many are removed, so the charge is ten times larger.
• (4) This is the charge of one electron, 1.6×10⁻¹⁹ C, with its coefficient dropped and quoted as though it were the charge of the whole plate. It still has to be multiplied by the number of electrons taken away.

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