Physics unit 3 sheet 2
- Created by: Will wretham
- Created on: 25-11-16 19:53
View mindmap
- Lenses and the eye
- Ciliary muscles adjusts the lenses thickness
- Refractive index is the degree at which a material slows down the speed of light compared to its speed in a vacuum
- Lenses and the Critial angle
- A formula to work out the critical angle is n(refractive index) = 1/sinc
- Circular motion
- The objects velocity is directed along the tangent of the circle. this means that the directions is constantly changing.
- The Force = mass X acceleration
- The acceleration is always towards the centre of the circle because the velocity is towards the centre of the circle.
- The direction always changes but the speed stays the same
- The acceleration of the object is called the centripetal acceleration
- The resultant force is always moving towards the centre of the circle and we call this force the centripetal force.
- The centripetal force can be increased by increasing the mass / increasing the speed / decreasing the radius of the circle
- X-rays and Ultrasound
- X-rays are very high frequency transverse waves which are very dangerous because they are ionising
- Ultrasound waves are longitudinal waves and these have a frequency of above 20'000 hertz(high)
- Properties of X-rays = absorbed by metal and bone, transmitted by healthy tissue, affect a photographic film, short wave length, high frequency, ionising.
- A CCD is used instead of a photographic film and modern X-rays machine can process images to be saved and stored electronically.
- Both X-rays and ultrasound are non-invasive and painless.
- X-rays help medical surgeons plan their operation because you can clearly see inside the body.
- X-rays can be processed by a computer to produce a 3D image
- CT scans are called tomograms and are more detailed than X-rays because they show inside vessels and organs
- Ultrasound is used for pregnancy scans and to see if the baby is developing correctly
- Ultra sound can also be used to smash kidney stones
- Ultrasound waves are partially reflected at each interface between different tissues.
- The ultrasound image is not as clear as the X-rays because the waves are only partly reflected
- On the oscilloscope always remember to halve the answer if it asks for the distance because the time is for it to be reflected back as well
Comments
No comments have yet been made