Physics P3.1
- Created by: Will Pound
- Created on: 03-03-14 17:34
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- Physics P3.1
- X-Rays
- Used in hospitals
- To make images and CT scans
- To destroy tumours at or near the body surface
- Can damage living tissues as they pass through
- Are absorbed more by bones than soft tissue
- Used in hospitals
- Ultrasound
- Are sound waves of frequency above 20,000Hz
- Used for diagnosis & treatment
- Ultrasound waves are partly reflected at a boundary between two different types of body tissue
- An ultrasound scan is non-ionising so it is easier than an X-ray
- Refractive index (n)
- Refraction is the change of direction of light as it passes from one transparent substance to another
- Refraction happens because waves change speed when they cross a boundary
- Is a measure of how much a substance can refract a light ray
- n=sin i / sin r
- Refraction is the change of direction of light as it passes from one transparent substance to another
- The endoscope
- The critical ange is the angle of incidence of a light ray in a transparent substance which produces refraction along the boundary
- n= 1 / sin c
- Total internal reflection occurs when the angle of incidence of a light ray in a transparent substance is greater than the critical angle
- An endoscope is used to see inside the body directly
- Lenses
- A converging lens focuses parallel rays to a point call the principle focus
- A diverging lens makes parallel rays spread out as if they came from a point called the principle focus
- A real image is formed by a converging lens if the object is further away than the principle focus
- Magnification = Image height / object height
- Using lenses
- A ray diagram can be drawn to find the position and nature of an image formed by a lens
- A camera contains a converging lens that is used to form a real image of an object
- A magnifying glass is a converging lens that is used to form a virtual image of an object
- The eye
- Light is focused on to the retina by the cornea and the eye lens, which is a variable focus lens
- The normal human eye has a range of vision from 25cm to infinity
- P= 1 / f
- Short sighted
- See near objects
- Use diverging (Concave) lens to correct it
- See near objects
- Long sighted
- See distant objects
- Use converging (Convex) lens to correct it
- See distant objects
- X-Rays
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