P3.1 Flashcards
Why is the handle for a door in the position that it is?
It’s the biggest distance from the hinges
What can turning effects also be called?
Moments
What does a lever do?
Changes the size of a force
What is the effort?
The force you exert on the lever
What is the load?
The force that the object being moved exerts on the lever
What is the pivot / fulcrum?
The point the lever turns about
What is the frequency and wavelength of X-rays?
~ High frequency
~ Very short wavelength (about the size of an atom)
What does the high frequency of X-rays mean?
They have a high energy and can cause ionisation
What is the high ionising power of X-rays used for?
Killing cancer cells in radiotherapy
X-rays are transmitted by healthy tissue, what is this property used for?
CT scans to detect soft tissue problems (eg disease, tumours, embolisms and haemorrhages)
X-rays are absorbed by bones and metals, what is this property used for?
Taking shadow pictures of bones to detect breaks and fractures
X-rays affect photographic film, what is this property used for?
Forming an image on an X-ray plate or with a CCD
What precautions are taken when using X-rays?
~ Use a focused beam so other parts of the body aren’t exposed
~ Technicians should take the X-ray from behind a screen or wear las clothing
~ Use as low a power as possible
What is the range of human hearing?
20Hz-20,000Hz
What happens as ultrasonic waves pass from one substance into another?
They’re partly reflected at the boundary (the time taken for these reflections is a measure of how far away the boundary is)
Reflected ultrasonic waves are usually processed to produce what?
A visual image on a screen
What is ultrasound used for?
~ Prenatal scans and other scans (eg detection of testicular cancer)
~ To break up kidney stones
How is ultrasound used in prenatal scans?
~ An ultrasound pulse is sent into the body and reflected back at different changes of density
~ These reflected waves are detected and used to form a picture of the foetus
What causes some of the ultrasound waves to be reflected?
Cracks within structures (the time taken for the reflected wave to return is used to calculate the location of the crack)
What can the vibrations caused by the ultrasonic waves be used for?
Cleaning delicate objects
What is the image quality and radiation exposure of CT scans?
~ Very good image quality
~ Longest exposure to ionising radiation
What is the image quality and radiation exposure of X-rays?
~ Good image quality
~ Short exposure to ionising radiation
What is the image quality and radiation exposure of ultrasound scans?
~ Good quality image depending on equipment
~ No exposure to ionising radiation
What is the process of bending light which is used in lenses?
Refraction
What are the 2 types of lens?
Diverging (concave) and converging (convex)
What is the difference between diverging and converging lenses?
They have a different curvature, so parallel rays of light pass through them differently
What is the focal length?
The distance from the lens to the principal focus
What is a diverging (concave) lens like at its centre?
It’s thinnest
What is a converging (convex) lens like at its centre?
It’s thickest
What do the rays of light do in a double concave lens?
Refract outwards at the 2 curved boundaries so that they appear to come from one point, the focus
What does only the middle ray in both diverging and converging lenses do?
Enters the lens at 90 degrees and passes straight through
What do the rays of light do in a double convex lens?
They’re refracted inwards at the two curved boundaries to meet at one point called the focus
What is the image produced by a converging (convex) lens like if the distance from the object to the lens is MORE than the distance from the lens to the focal point?
~ Real image
~ Inverted
~ Diminished
(the type of lens used in cameras)
What is the image produced by a converging lens like if the distance from the object to the lens is LESS than the distance from the lens to the focal point?
~ Virtual image
~ Upright
~ Enlarged
~ Seems to be formed on the same side of the lens (the type of lens used in magnifying glasses)
What is the frequency?
The number of waves passing a point per second
What is ultrasound?
Sound waves of frequencies greater than 20,000Hz
Why is ultrasound safer than using X-rays?
Ultrasound is non-ionising
What is the image produced by a diverging (concave) lens like?
~ Virtual
~ Upright
~ Diminished
What lens is used to correct short sightedness?
Diverging (concave) lens
What do the ciliary muscles in the eye do?
Pull the lens for focusing
What does the cornea in the eye do?
Lets light into the eye and begins focusing
What does the iris in the eye do?
Controls the amount of light entering the eye
What does the lens in the eye do?
Focuses light onto the retina
What does the optic nerve in the eye do?
Sends signals to the brain
What does the pupil in the eye do?
Let’s light through to the lens
What does the retina in the eye do?
It’s a light sensitive layer that sends signals to the optic nerve
What do the suspensory ligaments in the eye do?
Holds the lens in place
How do you know whether the image produced through lenses is virtual or real?
Virtual images are formed from imaginary, dotted lines and are on the same side of the lens as the object
How does ultrasound work through a transducer?
~ Ultrasound waves partially reflected when they meet different media
~ Time taken for reflections is measured
~ Each boundary distance is measured
~ Image formed on screen
What does it mean if you’re short sighted?
~ The eyeball is too long or the lens is too fat
~ Close objects are in focus but distant objects are focused in front of the retina
What does it mean if you’re long sighted?
~ The eyeball is too short or the lens is too thin
~ Distant objects are in focus but close objects are focused behind the retina
What lens is used to correct long sightedness?
Converging (convex) lens
How do eyes and cameras both allow light to enter?
~ Eyes use the pupil
~ Camera uses the aperture
How do eyes and cameras both focus light?
~ Eye uses cornea and lens
~ Camera uses convex lens
How do eyes and cameras both adjust focuses for different distances?
~ In the eye muscles and ligaments alter shape of lens
~ In cameras the lens moves closer to or further from the film/CCB chip
How do eyes and cameras both control the amount of light entering?
~ In the eye the iris changes the pupil size
~ In cameras the diaphragm/aperture stop changes the aperture size
How do eyes and cameras both form the images?
~ Eye uses the retina
~ Camera uses photographic film or CCD chip in digital cameras
What is similar about the images produced by eyes and cameras?
They’re real, inverted and diminished
What are lasers used for in medical physics?
~ Burning and cutting things
~ Cauterising (sealing off) things, such as damaged blood vessels
~ Reshaping cornea in laser eye surgery to enhance the bending of light that glasses would do
What can total internal reflection be used for?
~ Sending light along optical fibres, which can be used for telephone calls and the Internet
~ With an endoscope for internal examinations which stops the need for surgery to look in the patients body. The optical fibre illuminates by shining a light through the fibre
What is total internal reflection?
When all the rays are reflected and none are refracted
When does total internal reflection happen?
When the angle of incidence is bigger than the critical angle
How can the focal length be changed?
~ A more curved lens has a higher power and shorter focal length
~ A material with a high refractive index has a higher power and shorter focal length
How can lenses be made flatter but with the same focal length?
By having a higher refractive index
What is the unit for moments?
Nm
