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Flip to reveal answersDefine the electronvolt (eV).
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All 12 Flashcards — The electronvolt
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Question
Define the electronvolt (eV).
Answer
The **energy gained by one electron** when it moves through a potential difference of **one volt**. It is a unit of energy.
Question
How many joules is 1 eV?
Answer
**1 eV = 1.60 × 10⁻¹⁹ J** — given in the data booklet.
Question
Why is 1 eV = 1.60 × 10⁻¹⁹ J?
Answer
Energy = charge × voltage. The electron's charge e = 1.60 × 10⁻¹⁹ C, so crossing 1 V gives it 1.60 × 10⁻¹⁹ J.
Question
How do you convert eV → J?
Answer
**Multiply** the number of eV by 1.60 × 10⁻¹⁹.
Question
How do you convert J → eV?
Answer
**Divide** the energy in joules by 1.60 × 10⁻¹⁹.
Question
What is 1 keV in eV?
Answer
**1 keV = 10³ eV** (a kilo-electronvolt).
Question
What is 1 MeV in eV?
Answer
**1 MeV = 10⁶ eV** (a mega-electronvolt). Nuclear energies are usually quoted in MeV.
Question
Why do physicists use the eV instead of the joule?
Answer
Atomic and nuclear energies are tiny fractions of a joule; the eV gives convenient, easy-to-read numbers.
Question
Roughly how many eV is a visible-light photon?
Answer
A **few eV** (about 2 eV) — that is why atomic transitions emit visible light.
Question
Roughly how many MeV is a nuclear decay energy?
Answer
A **few MeV** — about a million times bigger than an atomic-transition energy.
Question
E = hf gives energy in which unit?
Answer
**Joules (J).** Convert to eV at the end (÷ 1.60 × 10⁻¹⁹) only if the question asks for eV.
Question
Convert 5.0 eV to joules.
Answer
5.0 × 1.60 × 10⁻¹⁹ = **8.0 × 10⁻¹⁹ J** (eV → J, so multiply).
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Structure of the atom
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