3a Flashcards
Name three ways X-rays are used in medicine?
Medical diagnosis, CT scans, treat cancer
What are X-rays?
High frequency, short wavelength EM waves
How can X-rays treat cancer?
The X-rays are focused on the tumour using a wide beam, this beam is rotated around the patient, this minimises the exposure of normal cells to radiation, and so reduces the chances of damaging the rest of the body.
What is Ultrasound?
Ultrasound is sound with a higher frequency than we can hear
Do Ultrasound waves get reflected at a boundary between media?
Partially
What can you use to find boundaries?
Oscilloscope
What formula can you use to work out the distance between the boundaries?
S = V X T s= distance in metres, m v= speed in metres per second, m/s t= time in seconds, s
What are some uses of ultrasound?
Medicine— breaking down kidney stones, pre-natal scanning of a fetus
What is refraction caused by?
The waves changing speed
What is a refractive index?
The ratio of speed of light in a vacuum to see of light in that medium
How do you work out the refractive index?
sin incident ray/ sin refracted ray
What is a converging lens?
A converging lens is convex- it bulges outwards. It causes parallel rays of light to converge (move together) at the principal focus
What is a diverging lens?
A diverging lens is concave- it caves inwards. It causes parallel rays of light to diverge (spread out)
What is the axis of a lens?
A line passing through the middle of the lens
Where is the principal focus of a converging lens?
Where rays hitting the lens parallel to the axis all meet
Where is the principal focus of a diverging lens?
Point where rays hitting the lens parallel to the axis appear to come from
DIVERGENT?
THEO JAMES
What is focal length?
The distance from the centre of the lens to the principal focus
What is a real image?
Where the light from an object comes together to form an image on a ‘screen’- like the image formed on an eyes retina
What is a virtual image?
When the rays are diverging, so the light from the object appears to be coming from a completely different place
What three things do you need to mention to describe an image properly?
1) How big it is compared to the object
2) Whether its upright or inverted relative to the object
3) Whether its real or virtual
What type of image does a diverging lens always produce?
A virtual image
What type of lens does a magnifying glass use?
Converging lens (magnified virtual image)
What is the magnification formula?
Magnification= image height / object height
The more powerful the lens, the more what it converges rays of light and therefore the what the focal length?
Strongly, shorter
What formula do you need to work out the power of a lens?
Power(D) = 1/ Focal length
What two factors is the focal length of a lens determined by?
The refractive index of the lens material, the curvature of the two surfaces of the lens
What happens to the power of the lens if the curve becomes more strong?
The lens is more powerful
What is the cornea?
A transparent window with a convex shape and a high refractive index. The cornea does most of the eye’s focusing
What is the iris?
The coloured part of the eye. Controls the size of the pupil and therefore the intensity of light that enters the eye
What is the role of the lens (in an eye)?
Focuses light from objects at varying distances
What is the image formed on in the eye?
The retina
How does a camera form images in a similar way to the eye?
The image on the film is a real image because light rays actually meet there. The image is smaller that the object, because the objects a lot further way than the focal length of the lens. Film in camera is equiv to the retina in our eye
Name two causes of short sight
Long eyeball, too powerful cornea or lens
Name two causes of long sight
Short eyeball, too weak cornea or lens
What kind of lens can short sight be corrected with?
Diverging- diverges the light before it enters the eye which means the lens can focus it on the retina
What kind of lens can long sight be corrected with?
Converging- the light is refracted and starts to converge before it enters the eye which means the lens can focus it on the retina
How can lasers be used in surgery?
To vaporise some of the cornea to change its shape- this changes its focusing ability, can increase or decrease the power of the cornea so that the eye can focus images properly on the retina
How can light be sent along optical fibres?
Total internal refraction
If a wave travels through a dense substance like glass or water towards a less dense substance like air, can total internal refraction take place?
Indeedydoody
Name two materials X-rays are absorbed by
Bones and metal
What is a charge-coupled device?
A device that detects X-rays ad produces electronic signals which are used to form high resolution images
Explain why ultrasound rather than X-rays are used to take images of a foetus
X-rays are ionising and therefore can cause cancer, not safe to use on babies
What is the critical angle?
The smallest angle of incidence for which light is totally reflected
A dense material with a high refractive index has a what critical angle?
A low critical angle
What formula relates refractive index and critical angle (c)?
Refractive Index= 1/ sin c
What is an endoscope?
A thin tube containing optical fibres that lets surgeons examine inside the body
