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Which physical quantity is measured in watts ()?
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9. Work & Energy
Power
Scelta multipla
If a monochromatic light source has a power output of (where ), and each photon has energy , how many photons are emitted per second?
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Identify the given quantities: the power output of the light source is 1 watt (W), which means it emits 1 joule (J) of energy per second (s). Each photon has an energy denoted by \( E \).
Recall the relationship between power, energy, and time: power \( P \) is the rate of energy transfer, so \( P = \frac{\text{energy}}{\text{time}} \). Here, the total energy emitted per second is 1 joule.
Understand that the total energy emitted per second is the sum of the energies of all photons emitted in that second. If \( N \) is the number of photons emitted per second, then the total energy per second is \( N \times E \).
Set up the equation relating power and photon energy: \( P = N \times E \). Since \( P = 1 \) watt, this becomes \( 1 = N \times E \).
Solve for the number of photons emitted per second \( N \) by rearranging the equation: \[ N = \frac{1}{E} \]. This gives the number of photons emitted per second in terms of the photon energy \( E \).
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