Light and electromagnetic waves (separate science) Flashcards
What are the safety precautions that somebody needs to take if they are working with x-rays?
Wearing a flim badge: This detects the levels of radiation a person has been exposed to. If they have been exposed to too much then they cannot work with radiation for a period of time
Safety screens: Workers will stand behind a safety screen when they are using the radiation. The screen stops the radiation from getting to them
Explain how an X-ray image is formed
X-rays are generated in an x-ray tube and pass through the pateint to an x-ray film. Moden x-ray films are an electronic device called a Charge Coupled Device (CCD) which can detect x-rays.
The X-rays can pass through soft tissue (skin and muscle) to hit the film, but cannot pass through the bone. This creates a ‘shadow’ of the bone on the screen.
The bones look white on x-ray because the film starts white, and turns black if an x-ray hits it
Explain how an x-ray tube generates x-rays
In an x-ray tube, a wire is heated up which releases electrons. The electrons are then accelerated by an electric field and collide with a metal anode.
When the x-rays collide with the anode they slow down suddenly. The energy transferred away from the kinetic energy store when they slow down is relaeased as an electromagnetic wave (an x-ray)
What is a contrast media?
How is it used to help with medical x-rays?
A contrast media is a substance that x-rays cannot pass through.
It is injected into the body to highlight certain organs and structures (such as the kidneys and bladder) so that they can be seen on x-ray
Which two factors affect the dose of x-rays recieved by a patient?
- The intensity of the x-rays (how powerful they are)
- The length of time they are exposed to the radiation for
What is a Sievert?
How many milli Sieverts are in a Sievert?
The Sievert is the unit of biological radiation exposure. It tells you the dose of radiation you have been exposed to.
There are 1000 mSv in 1 Sv
What is the difference between an X-ray scan and a CT scan
An x-ray scan sends a beam of x-rays through the patient to hit a film. This creates a single 2D image.
A Computerised Tomography (CT) scan uses a beam of x-rays which spiral round the patient. This can be used to construct a 3D image in slices of the inside of the body.
What is the difference between the doses of radiation a person recieves in a CT scanner compared to a normal X-ray
The patient recieves a much higher does in a CT scanner than they do if they have a normal x-ray taken.
What is the law of reflection?
The law of reflection states that the angle of incidence is equal to the angle of reflection.
What is the difference between a real image or a virtual image?
A real image is an image that can be projected on a screen. This is becuase the device causes the rays of light to cross.
A virtual image is an image that cannot be projected onto a screen. This is because the device causes the rays of light to diverge (spread out)
What are the characteristics of the image formed by a mirror
- Lateral inversion - Things on the left appear to be on the right. Things on the right appear to be on the left
- Virtual image - the image cannot be projected on a screen
Draw a ray diagram showing the reflection of a light ray at an angle of incidence of 45o
What are the two types of reflection?
Which of these types will form a clear image when light reflects off it?
Specular reflection: All light rays which are parallel will be reflected in the same direction. This occurs if the surface is smooth
Diffuse reflection: Parallel light rays are not reflected in the same direction. This is becuase the surface is rought
If specular reflection occurs a clear image will be formed. If diffuse reflection occurs then a clear image is not formed.
Explain how to investigate the law of reflection
- Set up a mirror on a piece of paper.
- Draw a normal to the mirror on a piece of paper
- Dse a ray box to shine a ray of light at a mirror. measure the angle of incidence and the angle of reflection
- Change the angle of incidence by 5o and repeat the experiment
- Do this for at least 5 angles of incidence and observe the pattern created
Complete this ray diagram to show where the image will appear
Explain how this image shows that a mirror produces a virtual image
The solid lines represent the actual light rays. As the real light rays do not cross it does not form an image that can be shown on a screen.
This means that it is a virtual image.
When investigating refraction, explain how to meausre the angle of incidence or angle of refraction
angles of incidence and refraction are measured between the light ray and the normal
Draw a ray diagram to show the refraction of light at a boundary. The angle of incidence is 50o and the angle of refraction is 30o
Explain why ligh disperses when it passes through a prism
White light is made of all of the colours of light. Different colours of light refract by different amounts. Red light refracts the most and violet light refracts the least.
The refraction causes the light to spread out from each other
Explain how to investigate how the angle of incidence affects the angle of refraction
- Set up the equipment as shown in the diagram. Make sure the block is on a piece of paper with the normal drawn on it
- Shine a ray of light from the ray box into the block and mark on the paper the incident and refracted ray.
- measure the angle of incidence and the angle of refraction
- Increase the angle of incidence by 5o and measure the angle of refraction
- repeat the experiment increasing the angle of incidence by 5o each time. take at least 5 readings
- plot a graph of the angle of incidence against the angle of refraction.
Explain the water in a swimming pool does not look as deep as it actually is
The light moving from the floor of the pool to the surface is refracted when it breaks the water. This bends it away from the normal so the light becomes more horizontal. The result is that the floor seems to be higher up,
Explain why some colours of light refract more than others
How does this explain light dispersal by a prism?
Different colours of light will travel at different speeds when passing through a medium that is not a vacuum
The longer the wavelength of the ligh, the greater the change of speed when it passes from one medium to another. If there is a greater change of speed, then there will be the largest amount of refraction
As red light has the longest wavelength it is refracted the most by a prism. As violet light has the shortest wavelength it refracts the least. This means that the light spreads out as they all leave the prism at different angles
What is the visible light spectrum?
The visible light spectrum is a continuous range of wavenegths that can be detected by the human eye. It ranges from a wavelengh of 400nm (violet light) to 750 nm (red light)
Explain how objects can have a colour
Objects will reflect some colours of light and absorb others. Coloured objects will absorb all colours of light apart from the colour that it is, which it reflects back.
For example, with a red object, white light will hit it which contains all the colours in the visible spectrum. All of the colours in the white light is absorbed aside from the red light, wich is reflected back and detected by the eye. This means that the eye sees it a red
Explain how a filter changes the colour of light, for example an orange filter
A filter will absorb all of the colours of light apart from the colour of the filter, which it allows through.
For example, an orange filter will only let orange light pass through and absorbs all of the other colours. This means that only orange light shines through the filter and onto the surroundings
What colour would a green object appear to be in
a) green light
b) red light
c) white light
Explain your answer
a) In green light the object would appear to be green. This is becuase it reflects the green light to the observer.
b) In red light the object will appear to be black. This is becuase it absorbs red light, and will not reflect back any light
c) In white light the object will appear to be green. This is because it abosrbs all colours of light apart from green, which it reflects back.
Explain why no light would get through two filters, if one is blue and the other is red
A filter will only allow through the colour of the light that matches the colour of the filter.
When the light passes through the red filter all of the colours in light are absorbed aside from red. Then when that red light hits the blue filter the red light is absorbed, as it would only let blue light through.
As there is no blue light left to pass through after the first filter, no light will pass through them both together..
What are the secondary colours of light and which primary colours need to be mixed to make them?
Yellow - created by green and red
Cyan - created by green and blue
Magenta - created by red and blue
What is the difference between a converging and a diverging lens?
A converging lens causes parallel rays entering the lens to move towards each other when they exit
A divierging lens causes parallel rays to move away from each other when they exit
What type of lens is this?
Draw the effect it has on parallel rays
This is a converging lens
What type of lens is this?
Draw the effect it has on parallel rays
This is a diverging lens
Explain how to identify if an image is a real image or a virtual image.
Example: What type of image is this?
An image is a real image if the actual rays cross (solid lines). An image is a virtual image if the actual rays diverge from each other, and the virtual rays (dashed lines) cross.
What is the equation that relates image size and object size.
Example: An object has a height of 3cm and a lens produces an image of 13.5cm height. What is the magnification of the image?
The equation for magnification is
M = I/O
M = magnfication
I = image height (m)
O - object height (m)
Example:
the image height is 0.135m, the object height is 0.03m
magnifcation = 0.135/0.03
= 4.5x
What is the focal point of a lens
In relation to a converging lens, what happens to ray if:
a) it hits the lens while travelling parallel to the principle axis
b) it travels through the focal point and then hits the lens
The focal point is the point that converging lenses bend rays towards if they are travelling parallel to the principle axis and diverging lenses bend rays directly away from if the rays are travelling parallel to the principle axis.
a) the ray will be refracted towards the principle axis and will pass through the focal point
b) the ray will be bent so it is running parallel to the principle axis
Explain how to use a ray diagram to determine if a lens will generate a real or virtural image and the magnification of that image.
- Draw the object and the principle axis. Make sure that the object height is drawn to a scale.
- Draw in the focal points on the principle axis
- Starting at the top of the image, draw a ray running parallel to the principle axis until it hits the lens. Then draw the ray from the lens to pass through the focal point on the other side of the lens
- Draw another ray passing through the centre of the lens straight through
- If the object is further away than the focal point. Draw a ray from the top of the image through the focal point. Once it hits the lens draw the ray leaving parallel to the focal point
- if the lines cross draw in the object so it ends where the lines cross. This is a real image
- if the lines do not cross extrapolate the lines backwards onto the same side of the lens as the object until they do cross. draw in the object where the lines cross, this is a virtual image
- measure the height of the image and use this to calculate the magnification of the lens
Explain ho to draw a ray diagram that shows the image formed by a diverging lens
- Draw the object and the principle axis. Make sure that the object height is drawn to a scale.
- Draw in the focal points on the principle axis
- Starting at the top of the image, draw a ray running parallel to the principle axis until it hits the lens. Then draw the ray from the lens directly away from the principle focus on the same side
- Draw another ray passing through the centre of the lens straight through
- extrapolate the lines backwards onto the same side of the lens as the object until they do cross. draw in the object where the lines cross, this is a virtual image
- measure the height of the image and use this to calculate the magnification of the lens
Explain how a camera uses a converging lens to create an image
Which type of image does a camera create
A camera will refract the rays of light so that they all focus on a point. Where the rays cross the image is in focus.
If a photographic film or a charge coupled device (CCD) is placed where the rays cross, a focussed image will be created
A camera lens can be altered to change the focal length of the camera. This is done to ensure that the rays cross the correct distance away to form an image on the film
Cameras create a real inverted image
What is the difference between an upright and an inverted image
An upright image ic created in the same orientation as the original object
An inverted image is upside down compared to the original object
Explain how a magnifying glass works
Why can you see a focussed image even though it is virtual?
A magnifying glass is a diverging lens. When light passes through it it causes it to bend away from the focal point. Magnifying glasses create an upright image which allows us to interpret what we are seeing easily
We can see the image created becuase the lens in our eye acts as a second lens to focus the light rays which have passed through the magnifying glass and are now diverging. This allows a real image to be created on the retina of our eye
