X-Rays, Ultrasound, Refractive Index Flashcards
When an X-ray photograph is taken, why is it necessary to place the patient between the X-ray tube and the film cassette?
To create an image, X-rays not absorbed by bones etc must reach the film cassette. Due to this, the X-ray tube is pointed at the film cassette. The patient is put between the X-ray tube and the receiver, so that different parts of the body will absorb X-rays and some will not, forming an image where at places X-rays have reached the film it is black, and where it has been absorbed by bone, and therefore X-rays have not reached the scanner, it is white. This creates an image of the patient.
Complete the statements:
1: X-rays ________ thin metal sheets
2: Thick lead plates will ________ X-rays
3: X-rays ________ living tissue
Missing Words:
Absorb
Damage
Penetrate
1: X-Rays penetrate thin metal sheets
2: Thick lead plates will absorb X-rays
3: X-Rays damage living tissue.
When an X-ray photograph is taken, why is it necessary to have the film in a lightproof cassette?
If the film was not in a lightproof cassette, it would react with the light and turn white before the x-rays reach it, meaning the entire image would act as if x-rays had reached the entire piece of film.
When an X-ray photograph is taken, why is it necessary to shield those parts of the patient not under investigation from X-rays?
X-Rays damage living tissue, so it is important to shield as much tissue as possible.
State one advantage and disadvantage that CT scanners have over X-rays.
Advantages:
•Distinguishes between different types of soft tissue
•Creates a three-dimensional image
Disadvantages:
•Machine more expensive
•CT Scanners give a higher dose of radiation than X-rays
Why are ultrasound waves partly reflected by body organs?
When the material in which the sound wave is travelling through changes, some of the sound is reflected back.
Why are X-rays used in hospitals? (2 Reasons)
- To make images and CT scans
* To destroy tumours at or near the body surface
What are ultrasound waves?
Sound waves of frequency above 20 000 Hz
Why are ultrasound waves used in medicine? (2 uses)
Ultrasonic scanning and the destruction of kidney stones
Why is an ultrasound scanner better than an X-Ray for scanning a body organ?
Ultrasound Waves are:
•Non-ionising and therefore harmless when used for scanning
•Reflected at boundaries between different types of soft tissue so can be used to scan organs and other soft tissues.
What is Refractive index?
Refractive index, n, is a measure of how much a substance can refract a light ray.
Complete the statements with either “more” or “less”:
1: When a light ray travels from air to glass, the angle of refraction is always ________ than the angle of incidence
2: When a light ray travels from water into air, the angle of incidence in the water is ________ than the angle of refraction in air.
3: When a light ray travelling from air into glass is refracted, reducing the angle of incidence makes the angle of refraction ________ .
1: Smaller
2: Smaller
3: Smaller
What is the equation for working out the refractive index?
sin i
n= ——-
sin r
