Physics Further

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X-rays
High frequency and a very short wavelength
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Properties of X-rays
They affect a photographic film in the same way as light. They are absorbed by metal and bone. They are tranmitted by healthy tissue.
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Charge-coupled devices
CCD's can be used to form electronic images of x-rays. CT scanners use x-rays to produce images of the body.
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Damage by X-rays
X-rays can cause ionisation and can damage living tissue, therefore workers wear film badges and when possible use lead screens to sheild themselves.
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Ultrasound
Sounds waves higher than 20,000Hz. Non-ionising so is safer to use than X-rays
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Ultrasound equation
S=V x T. S is the distance travelled in metres. V is the speed of the ultrasound wave in metres per second. T is the time taken in sections.
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Refractive index
n=sin(i)/sin(r) The refractive index of a substance is a measure of how much the substance can refract a light ray.
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Total internal reflection
If the angle of incidence is increased beyound the critical angle the light ray undergoes total internal reflection. This is when the angle of reflection is equal to the angle of incidence. Only takes place from a more dense to a less dense material
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Critial angle
n=1/sin(c) n is the refractive index. c is the critical angle
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Endoscope
Is a devise used to look inside the body without cutting it open or in key hole surgery. Uses optical fibres.
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Optical fibres
Thin, flexible glass fibres. Visible light can be sent along the fibres by total internal relfection.
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Convex lense
Converging lense, arrows point outwards, thin ends. Real image
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Concave lens
Diverging lends, arround point inwards, thick ends. Virtual image
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Magnification
magnification = image height/object height
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Principal axis
The line through the centre of a ray diagram is called the principal axis.
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Camera
A camera uses a converging lens to form a real image of an object on a film or an array of CCD's
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The eye
Light enters through the cornea. The cornea and the eye lens focus the light onto the retina. The iris adjusts the size of the pupil to control the light amount entering. Ciliary muscles alters the tickness of the lens, joined by suspensory ligaments
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Normal human eye
The normal human eye has a near point of 25cm and a far point of infinity, so its range of vision is from 25cm to infinity
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Lens power
P=1/f P is the power of the lends in dioptres D. f is the focal lenth of the lens in metres
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Short sight
Short sight is caused by the eyeball being too long or the eye lens being too powerful. Short sight may be corrected using a diverging lens.
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Long sight
Long sight is caused by the eyeball being too short or the eye lens being too weak. Long sight may be corrected using a converging lends.
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Focal length is determined by:
1. the refractive index of the material from which the lends is made. 2. The curvature of the two surfaces of the lens. For a lens of a given focal length, the greater the refractive index of the lens material, the flatter and thinner the lens can be
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Moments
M = F x D M is the moment of the force in newton-metres. F is the force in newtons. D is the perpendicular distance from the line of action of the force to the pivot in metres
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Centre of mass
1. Suspend the thin sheet from a pin. 2. when it comes to rest hand a plumbline from the pin. 3. mark the position of the plumbline against the sheet, repeat process from other points. 4. where the lines marked cross is the centre of mass.
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Equilibrium
Any object that is freely suspended will come to rest with its centre of mass directly below the point of suspension. The object is then in equilibrium
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Resultant moment
If the line of action of the weight lies outside the base of an object, there will be a resultant moment and the object will tend to topple over
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Pressure
P=F/A P is the pressure in pascals. F is the force in newtons. A is the cross sectional area at right angles to the direction of the force in metres squared
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The force exerted by a hydraulics pressure system depends on:
1. the force exerted on the system. 2. the area of the cyclinder on which the force acts on. 3. the area of the cyclinder that exerts the force
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Pressure transmitted
The pressure transmitted is the difference of the two forces in pascals. Pa.
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Centripetal force
An object only accelerates when a resultant force acts on it, this force is called the centripetal force and always acts towards the centre of the circle.
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Centripetal acceleration
When an object moves in a circle it is continuously changing direction, so it is continuously changing velocity. In other waters it is accelerating. This acceleration is called the centripetal acceleration
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The centripetal force increases as:
1. the mass of the object increases. 2. the speed of the object increases. 3. the radius of the circle decreases
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Oscillating motion
A pendulum moves to and fro along the same line
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Time period
The time period for an oscillation is the time taken from one complete cycle, this is from the highest point on one side to the highest point on the other side and back to the start position
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Time period equation
T = 1/F T is the time period in sections. f is the frequency in hertz
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Electromagnets
When a current flows through a wire a magnetic field is produced around the wire. An electromagnet is made by wrapping insulated wire around a piece of iron called the core. When a current flows through the wire the iron becomes strongly magnetised.
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Electromagents examples
Electromagnets are used in devices such as scrapyard cranes, cicuit breakers, electric bells and relays
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The motor effect
When we place a wire carrying an electric current in a magnetic field, it may experience a force.
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Fleming's left hand rule
The first finger represents the magnetic field pointing north to south. The second finger represents the current pointing positive to negative. The thumb represents the direction of the force
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Split ring commutator. The electric motor
The split ring commutator reverses the direction of the current around the coil every half turn. Because the sides swap over each half-turn, the coil is always pushed in the same direction.
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Electromagnetic induction
If a magnet is moved into a coil of wire a pd is induced across the ends of the coil. This process is called electromagnetic induction, but only is there is movement.
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Step-up transformer
Makes the pd across the secondary coil greater than the pd across the primary coil. Its secondary coil has more turns than its primary coil.
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Step-down transformer
Makes the pd across the secondary coil less than the pd across the primary coil. Its secondary coil has fewer turns than its primary coil
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Transformers - primary coil
A transformer is two coils of insulated wire. These coils are wound on to the same iron core. When an alternating current passes through the primary coil, it produces an alternating magnetic field in teh core. This field continually expands and colla
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Transofmers - secondary coil
The alternating magnetic field lines pass through the secondary coil and induce an alternating potential difference across its ends. If the secondary coil is part of a compelte circuit an alternating current is produced.
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Switch mode transformer
Has a ferrite core. Compared to normal: operates at a might higher frequency. is lighter and smaller. uses very little power when there is no device connected across output terminals
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Examples of physics - ECG
An electrocardiogram is used to measure the pd generated by the heart.
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Examples of physics - MR scanners
Use radio eaves to produce detailed digital pictures of the body
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Other cards in this set

Card 2

Front

They affect a photographic film in the same way as light. They are absorbed by metal and bone. They are tranmitted by healthy tissue.

Back

Properties of X-rays

Card 3

Front

CCD's can be used to form electronic images of x-rays. CT scanners use x-rays to produce images of the body.

Back

Preview of the back of card 3

Card 4

Front

X-rays can cause ionisation and can damage living tissue, therefore workers wear film badges and when possible use lead screens to sheild themselves.

Back

Preview of the back of card 4

Card 5

Front

Sounds waves higher than 20,000Hz. Non-ionising so is safer to use than X-rays

Back

Preview of the back of card 5
View more cards

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