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Monochromatic light of frequency 6×10¹⁴ Hz is produced by a laser. Each photon has an energy of ______ J.

Asked in GSEB Board March 2020 · Photon energy, momentum and mass

• (1) 6×10¹⁴
• (2) 4×10⁻¹⁹
• (3) 4×10⁻²⁰
• (4) 6×10⁻¹⁴

Step-by-step solution

Why the other options are wrong

• (1) This is the frequency itself copied as the energy. A photon's energy is h u, so the frequency must be multiplied by h = 6.63×10⁻³⁴ J s.
• (3) Comes from dropping the power of ten carried by 6.63×6 = 39.8: the product is 39.8×10⁻²⁰ = 3.98×10⁻¹⁹ J, not 3.98×10⁻²⁰ J.
• (4) No single slip gives 6×10⁻¹⁴ J; it is the frequency with the sign of its exponent flipped. Sanity check: a visible photon carries a few times 10⁻¹⁹ J, here about 2.5 eV.

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