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Questions and Answers
What is the ratio of the speed of light in a vacuum to its speed in a given material called?
What is the ratio of the speed of light in a vacuum to its speed in a given material called?
- Speed of light coefficient
- Material density factor
- Light absorption ratio
- Index of refraction (correct)
How does light behave?
How does light behave?
- Only as a wave
- Both as a wave and as a particle (correct)
- Neither as a wave nor as a particle
- Only as a particle
What happens when light is absorbed by a molecule?
What happens when light is absorbed by a molecule?
- The molecule gains energy
- The molecule loses energy
- The molecule splits into two molecules
- The energy is released as heat (correct)
What type of reflection occurs when rough surfaces scatter light in many directions?
What type of reflection occurs when rough surfaces scatter light in many directions?
What is the unit of measurement for wavelength of light?
What is the unit of measurement for wavelength of light?
What is the main characteristic of ordinary light in terms of wavelength?
What is the main characteristic of ordinary light in terms of wavelength?
What is an endoscope used for?
What is an endoscope used for?
What is the reason behind the directional distribution of laser light?
What is the reason behind the directional distribution of laser light?
What instrument is used to examine the air passages into the lungs?
What instrument is used to examine the air passages into the lungs?
Which of the following is a characteristic of ordinary light?
Which of the following is a characteristic of ordinary light?
What is the category of light that is used to heat tissues?
What is the category of light that is used to heat tissues?
What happens to the intensity of ordinary light with distance?
What happens to the intensity of ordinary light with distance?
What is the main difference between ordinary light and laser light?
What is the main difference between ordinary light and laser light?
What is the coherence length of ordinary light?
What is the coherence length of ordinary light?
Why is it safe to look at an ordinary light source?
Why is it safe to look at an ordinary light source?
What is true about incandescent bulbs?
What is true about incandescent bulbs?
What is the process by which an incoming photon stimulates an electron to change energy levels?
What is the process by which an incoming photon stimulates an electron to change energy levels?
What is the origin of the word 'laser'?
What is the origin of the word 'laser'?
What is the characteristic of the emitted photon in stimulated emission?
What is the characteristic of the emitted photon in stimulated emission?
What is the result of concentrating the entire energy of a laser beam into a small area?
What is the result of concentrating the entire energy of a laser beam into a small area?
What is the unit of measurement for the total energy of a typical laser pulse used in medicine?
What is the unit of measurement for the total energy of a typical laser pulse used in medicine?
How is the output of a pulsed laser usually measured?
How is the output of a pulsed laser usually measured?
What is the effect of laser energy on human tissue?
What is the effect of laser energy on human tissue?
What determines the amount of damage to living tissue caused by laser energy?
What determines the amount of damage to living tissue caused by laser energy?
What is the main advantage of flexible endoscopes over rigid endoscopes?
What is the main advantage of flexible endoscopes over rigid endoscopes?
Why are UV photons more useful than IR photons?
Why are UV photons more useful than IR photons?
What is one of the beneficial effects of UV light on the skin?
What is one of the beneficial effects of UV light on the skin?
Why do people who work outdoors, such as fishermen and agricultural workers, have a higher incidence of skin cancer?
Why do people who work outdoors, such as fishermen and agricultural workers, have a higher incidence of skin cancer?
Why can you get a sunburn even when you are sitting in the shade?
Why can you get a sunburn even when you are sitting in the shade?
Why can't the eye see UV light?
Why can't the eye see UV light?
What happens when an electron makes a transition from a higher energy to a lower energy state?
What happens when an electron makes a transition from a higher energy to a lower energy state?
What is the difference between spontaneous emission and stimulated emission?
What is the difference between spontaneous emission and stimulated emission?
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Study Notes
Light in Medicine
- Light has interesting properties that are used in medicine, including:
- Changing speed when passing from one material to another
- Behaving as both a wave and a particle
- Being absorbed by a single molecule, resulting in various energy releases
- Being reflected from all surfaces, with two types of reflection: diffuse and specular
Measurement of Light and Its Units
- Light is divided into three categories: UV, Visible, and IR, based on their wavelengths
- Wavelengths can be measured in:
- Microns (1 μ = 10^-6 m)
- Angstroms (1 Ã… = 10^-10 m)
- Nanometers (1 nm = 10^-9 m)
Applications of Visible Light in Medicine
- Endoscopes are used to view internal body cavities
- Cytoscopes are used to examine the bladder
- Bronchoscopes are used to examine air passages into the lungs
- Flexible endoscopes can obtain information from regions that cannot be examined with rigid endoscopes
UV Light in Medicine
- UV photons have higher energies than visible and IR light
- UV light is used to sterilize medical instruments
- UV light produces reactions in the skin, including:
- Beneficial effects: conversion of molecular products into vitamin D
- Harmful effects: sunburn, tan skin, and skin cancer
- UV light has shorter wavelengths than visible light and is scattered more easily
Laser in Medicine
- Lasers operate on the principle of stimulated emission
- Stimulated emission has three important features:
- One photon goes in and two photons come out
- The emitted photon travels in the same direction as the incoming photon
- The emitted photon is coherent with the incoming photon
- Laser beams can be focused to a spot only a few microns in diameter
- The power density of a laser beam can be very large, causing rapid temperature rise and tissue damage
Ordinary Light and Laser Light
- Ordinary light is a mixture of electromagnetic waves of different wavelengths
- Laser light is monochrome and has a directional and consistent distribution
- Laser light is spectrally pure and has a focused beam with all photons moving at the same wavelength and direction
- Ordinary light is natural, while laser light is an induced emission
- Ordinary light is inconsistent, diffused, and has a short coherence length, while laser light is consistent, directional, and has a long coherence length
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