AQA Physics Unit 3

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Do x-rays have high or low frequencies?
High
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Do x-rays have long or short wavelengths?
Short
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X-rays affect which type of film in the same way as light?
Photographic film
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X-rays are absorbed by what?
Metal and bone
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Why can x-rays be harmful to the body?
Because they're ionising
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What do x-rays form images of?
Bone and metal
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Excluding bone, what else (that is naturally found) in the body may be (with human interference) seen using x-rays?
Some body organs such as he small intestine. They can be filled with a contrast medium that absorbs x-rays
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The human ear can detect frequencies between which two values?
20Hz and 20,000Hz
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What are sound waves with a frequency higher that 20,000Hz called?
Ultrasound
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Can x-rays be used to detect cancerous tumours?
No, but they can treat cancer
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What reflects ultrasound waves?
Boundaries between two different materials
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What is refraction?
The change of direction of light as it passes through one transparent substance to another
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Why does refraction occur?
Because the light waves change speed once they cross a boundary. This speed change causes a change in direction
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What is refractive index?
How much a substance refracts a light ray
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How can refractive index be calculated?
sin(i)/sin(r)
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When something is refracted, which angle is the angle of incidence?
The angle between the normal and the 'initial light ray'
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Where should the normal be drawn when a light ray is refracted?
Perpendicular to the edge of the substance (going straight through the block/substance)
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Where is the angle of refraction when alight ray has been refracted?
Between the normal and refracted ray (inside the substance and before it leaves)
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What is the ratio of refractive index?
It has no unit; it's a ratio
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Why is ultrasound safe?
Because it's non-ionising
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Why is ultrasound not used to diagnose?
Because the produced are fuzzy
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What happens when a way hits a boundary at 90 degrees (along the normal)?
It will not change direction but it will slow down
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Which direction does a wave bend when it slows down?
Towards the normal
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What type of lens bulges outwards?
Converging/ convex
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Which type of lens bulges inwards?
Diverging/ concave
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What does a diverging lens do to parallel light rays?
Spreads the rays out
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What does a covering lens do to parallel light rays?
Focuses them onto one point
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Where is the principal focus of a converging lens?
On the opposite side of the incident ray, where all of the rays (that are parallel to the axis) meet
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Where is the principal focus of a diverging lens?
On the side of the incident rays, the point where (when you trace backwards) the rays meet
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What is the focal length?
The distance from the centre of the lens to the the principal focus
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When will a ray pass through the principal focus?
When it's travelling parallel to the axis
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What is the axis?
A line passing through the middle of the lens
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When will a ray not change direction when passing through a lens?
When it's travelling along the axis
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What is a real image?
An image on the same side of the incident rays
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What is a virtual image?
An image on the opposite side to the incident ray
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To describe an image, what three things do you need to mention?
How big it is compared to the object, whether it's upright or converted and whether it's real or virtual
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How is visible light sent through an optical fibre?
Using total internal reflection
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How do you measure the critical angle?
1/sin(c)
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What is an endoscope?
Optical wires that are fed into someone's body via their mouth (or equivalent). The doctor can see an image
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What type of image does a converging lens produce?
Real if the object is further away than the principal focus but virtual if the object is nearer
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What type of image does a diverging lens produce?
Virtual.
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How can magnification be calculated?
image height/ object height
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If the arrows on a lens symbol are pointing inwards, what type of lens is it?
Diverging
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If the arrows on a lens symbol are pointing outwards, what type of lens is it?
Converging
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Which three constructive rays do you need to produce when drawing a ray diagram?
A ray from the top of the object that goes parallel to the principal axis (basically just the y axis), one that goes from the top of the object and through the centre of the lens (origin) and a final ray that goes through the principal focus
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What type of lens do cameras use, what type of image do they produce and what is the image produced on?
Converging/ concave, real image, photographic film/ CCDs
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What is the iris for?
Controls the amount of light that enters the eye
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Where is the iris located on an eye diagram and what does it look like?
In front of the lens (the sticky out bits), and it's the coloured bit
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What is the cornea for?
It protects the eye and helps focus light onto the retina
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Where is the cornea located on an eye diagram and what does it look like?
Right at the front of the eye, and it's transparent
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What is the pupil for?
It's the gap that the light goes through
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Where is the pupil located on an eye diagram and what does it look like?
It's the seemingly substance-less gap between the cornea and the iris
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What are the ciliary muscles for?
They change the thickness of the eye lens
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Where are the ciliary muscles located on an eye diagram and what does it look like?
On top and underneath the eye lens, they basically look like mini-muslces
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What are x-rays?
High frequency, short wavelength electromagnetic waves
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What are x-rays absorbed by?
Dense materials like bone or metal
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What can x-rays be used for?
Diagnosing medical conditions such as bone fratures and dental problems
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What are CCDs?
Charge-coupled devices that detect x-rays and form high-resolution images
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What do CT scans use? What for?
X-rays to form high-resolution images of soft and hard tissue
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What happens during a CT scan?
X-rays are fired through a patients bodyand picked up by detectors on the other side
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What is a downfall of x-rays?
They're ionising
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How can x-rays be used to treat cancer?
By focusing them on tumours (which will kill them)
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What are four ways in which radiographers can protect themselves from x-rays?
By wearing lead aprons, by standing behind a lead screen, by leaving the room and/or by simply limiting their work with x-rays
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Other cards in this set

Card 2

Front

Do x-rays have long or short wavelengths?

Back

Short

Card 3

Front

X-rays affect which type of film in the same way as light?

Back

Preview of the front of card 3

Card 4

Front

X-rays are absorbed by what?

Back

Preview of the front of card 4

Card 5

Front

Why can x-rays be harmful to the body?

Back

Preview of the front of card 5
View more cards

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