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Questions and Answers
What is the charge on an electron?
What is the charge on an electron?
- -e (correct)
- +e
- 0
- 2e
What is the term for the fact that electric charge is always an integral multiple of $e$?
What is the term for the fact that electric charge is always an integral multiple of $e$?
- Conservation of charge
- Quantisation of charge (correct)
- Charge conservation
- Electrolysis principle
What unit is used to measure electric charge in the International System of Units (SI)?
What unit is used to measure electric charge in the International System of Units (SI)?
- Coulomb (correct)
- Ohm
- Volt
- Ampere
Which of the following is approximately the value of the elementary charge $e$?
Which of the following is approximately the value of the elementary charge $e$?
How many electrons are approximately contained in a charge of -1C?
How many electrons are approximately contained in a charge of -1C?
What is the significance of the quantisation of charge at the macroscopic level?
What is the significance of the quantisation of charge at the macroscopic level?
What happens to the perception of charge at the macroscopic level?
What happens to the perception of charge at the macroscopic level?
Which scientist first suggested the concept of quantisation of charge?
Which scientist first suggested the concept of quantisation of charge?
What is the equivalent of 1 µC in coulombs?
What is the equivalent of 1 µC in coulombs?
How is the total charge of a body with $n₁$ electrons and $n₂$ protons calculated?
How is the total charge of a body with $n₁$ electrons and $n₂$ protons calculated?
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Study Notes
Electric Charge Fundamentals
- Basic Units of Charge: Charge is quantised in integral multiples of the elementary charge, symbolized as e.
- Charge Values:
- Electron: -e (negative charge)
- Proton: +e (positive charge)
Quantisation of Charge
- The phenomenon where electric charge cannot take arbitrary values, but only integer multiples of e, is known as quantisation of charge.
- Historical Context:
- Proposed by Michael Faraday's experimental laws of electrolysis.
- Verified by Robert Millikan in 1912 through the oil drop experiment.
Unit of Charge
- SI Unit: Coulomb (C)
- Definition: One coulomb is the amount of charge flowing through a conductor carrying one ampere of current in one second.
- Elementary Charge Value:
- ( e = 1.602192 \times 10^{-19} C )
- There are approximately ( 6 \times 10^{18} ) electrons in a charge of -1C.
Practical Units
- Smaller Units:
- 1 µC (microcoulomb) = ( 10^{-6} C )
- 1 mC (millicoulomb) = ( 10^{-3} C )
Charge Composition
- Total charge of an object can be calculated as:
- ( Q = (n_2 - n_1)e )
- Where ( n_1 ) is the number of electrons and ( n_2 ) is the number of protons.
- The nature of charge being an integral multiple of e leads to observable quantised values.
Macroscopic vs. Microscopic Perspective
- At a macroscopic level, charge appears continuous due to large values compared to e.
- Example: A charge of 1 µC contains about ( 10^{13} ) elementary charges (e).
- The quantisation is negligible at this scale, similar to how a dotted line appears continuous from a distance.
Implications
- Macroscopic Level: Quantisation of charge can be ignored for practical applications since charges are vastly larger than e.
- Microscopic Level: Charging phenomena become significant, especially when charges are measured in multiples of a few elementary charges.
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