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Flashcards in Physics a Deck (68)
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What are X-rays ?

High frequency, short wavelength electromagnetic waves


How can X-rays produce images of the inside of the human body ?

X-rays are transmitted through healthy tissue but absorbed by denser materials like bones. A photographic film changes colour when the X-rays touch it, so the areas where the waves can't pass through like bone or metal don't change colour. This creates a black and white image


What can X-Ray photographs be used for ?

To diagnose medical conditions such as bone fractures or dental problems


What is a new way in which X-ray photographs are formed ?

In the same way as digital cameras. Silicon chips detect rays and produce electronic signals which form high resolution images. They are known as CCDs


What does the CT in CT Scan stand for ?

Computerised axial tomography


How do CT scans work ?

The body part being scanned is put inside a cylinder in which one side emits x-rays and the other side detects it. As the cylinder rotates multiple images are taken, forming a 2D slice I the body part. Multiple slices can be put together to form a 3D image.


How can x-rays be used to treat cancer ?

X-rays cause ionisation - high doses can kill living cells. If focused at just the right dosage and area, cancerous cells can be killed without damaging normal cells.


What is ultrasound ?

Sound with a higher frequency than we can hear.


Above what frequency is ultrasound ?

Over 20,000 Hz


What frequency can humans hear ?

20-20,000 Hz


What is partial reflection ?

When a wave passes into a medium, some is reflected off the boundary and some refracts through that medium.


How does ultrasound imaging work ?

A detector measures the time it takes an ultrasound wave to reflect of a boundary between two mediums. The longer the time the further away the object.


How do you work out the distance between two boundaries ?

Speed x Time


How do ultrasound waves break down kidney stones ?

Kidney stones block the urinary tract, making it very painful to urinate. Ultra sound waves can be directed at the kidney stones to turn them into sand-like particles. These can then pass out of the body in urine.


Ultrasounds can monitor the development of a foetus, how is this done ?

The ultrasound waves reflect when they reach a different medium. They are detected and the exact time and distribution of echoes are recorded by a computer. This forms an image of the foetus.


Which is the safest way of creating image of the human body ?

Ultrasounds. They are non ionising which means they won't kill healthy cells, unlike X-Ray or CT scans


Which is more dangerous - X-Rays or CT scans ?

CT scans use a lot more x-ray radiation so the patient is exposed to even more radiation.


Which images are the most detailed ?

CT scans produce extremely detailed images in high resolution where as ultrasound images are fuzzy which makes it harder to diagnose illnesses. X-ray images are somewhere in the middle


Why do waves refract ?

As they pass into a different medium the waves change speed


What is the normal ?

A line perpendicular (90 degrees) to the boundary


What happens when a line hits the boundary at 90 degrees (the normal) ?

It will not change direction


True or false - when light hits a medium some will pass through some will be reflected

True - it changes depending on the size of the angle of incidence


What is refractive index ?

The ratio of speed of light in a vacuum to the speed of light in different mediums


What is the formula to work out refractive index ?

Sin i divided by Sin r

i = angle of incidence
r = angle of refraction


How do lenses form images ?

They refract light and change its direction.


What are the two main types of lenses ?

Converging and diverging


What does a converging lens do ?

It is convex which means it bulges outwards. It causes parallel rays of light to move together (converge) at the 'principal focus'


What does a diverging lens do ?

It is concave which means it caves inwards. It causes parallel rays of light to spread out (diverge)


What is the 'principal focus' point ?

The point where the rays all meet


How do you find the principal focus of a diverging lens ?

Because they all spread out there is no point where they all meet on the other side of the lens. Instead, the point is measured where the lines meet before hitting the lens