Chapter 38: Problem 4
A laser used to weld detached retinas emits light with a wavelength of 652 nm in pulses that are 20.0 ms in duration. The average power during each pulse is 0.600 W. (a) How much energy is in each pulse in joules? In electron volts? (b) What is the energy of one photon in joules? In electron volts? (c) How many photons are in each pulse?
Short Answer
Step by step solution
Understand Power and Energy Relationship
Calculate Energy in Joules
Convert Joules to Electron Volts
Determine Energy of One Photon in Joules
Convert Energy of One Photon to Electron Volts
Calculate Number of Photons in Each Pulse
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Laser Physics
Lasers have diverse applications, and one critical use is in medical fields like ophthalmology. For instance, in the case of welding detached retinas, the laser emits light with a specific wavelength, which is utilized to perform delicate surgical procedures.
- Laser light has a single wavelength, which means it is monochromatic.
- It remains focused over long distances due to the collimated beam.
- Laser beams are coherent, meaning the light waves are synchronized.
Energy Conversion
The relationship between power, energy, and time is expressed in the equation:
\( E = P \times t \).
Where:
- \( E \) is energy (in joules).
- \( P \) is power (in watts).
- \( t \) is time (in seconds).
Photon Quantity Calculation
Photons are tiny packets of light energy, each carrying an energy that can be determined with the equation:
\( E_{\text{photon}} = \frac{hc}{\lambda} \),where:
- \( h \) is Planck's constant \((6.626 \times 10^{-34} \text{ J} \cdot \text{s})\).
- \( c \) is the speed of light \((3.00 \times 10^8 \text{ m/s})\).
- \( \lambda \) is the wavelength in meters.
\[ \text{Number of Photons} = \frac{E}{E_{\text{photon}}} \].
This calculation yields the number of photons emitted in each pulse, shedding light on the quantum nature of light and providing insight into how lasers achieve their power and precision.