P3
- Created by: Reuben Cooper
- Created on: 05-05-13 09:56
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- P3
- Medical Applications of Physics
- X-Rays
- Short wavelength
- Can cause ionisation
- Affect a photographic film in the same way as light
- Can be detected using charge-coupled devices (CCDs) to form an image electronically
- CT Scans
- More detailed 2d and 3d images
- Image can be observed from any angle
- Increased levels of radiation for patient
- Higher resolution images
- More detailed 2d and 3d images
- Ultrasound
- Sound greater than 20,000 Hz
- Inaudible to humans
- Non-ionising
- Partially reflected at a boundary between two different media
- Uses
- Pre-natal scanning
- Imaging of damaged ligaments and muscles
- Destruction of kidney stones
- Sound greater than 20,000 Hz
- X-Rays
- Optics
- Lenses
- Converging (Convex)
- Image is real and inverted
- Image is smaller for distant objects
- Image is magnified for objects between F and 2F
- Light is refracted inwards and rays meet at F
- Can be used as magnifying glasses
- Diverging (Concave)
- Image is virtual
- Image is upright
- Rays of light diverge (separate) as they leave the lens
- Converging (Convex)
- Virtual
- Image is the same side as the object
- Real
- Image is on the opposite side to the object
- Refraction
- When light crosses a boundary between two different transparent media of varying densities, it changes direction
- No refraction occurs when light enters along the normal
- Angle of incidence, i
- Angle between ray entering a boundary and the normal
- Angle of refraction, r
- Angle between ray leaving a boundary and the normal
- Power
- One over focal length
- Converging lens
- Positive
- Real focal point
- Positive
- Diverging lens
- Negative
- Virtual focal point
- Negative
- Critical Angle
- Occurs when the angle of refraction equals 90 degrees.
- The light ray travels on the boundary between the media e.g. glass and air
- Diagram
- Total internal reflection
- Occurs when the angle of incidence is greater than the critical angle
- No refraction occurs so no light leaves the media
- Used in medical endoscopes to view the inside of the body
- Visible light directed along optical fibres to an eye piece or camera
- Magnifying glasses
- Convex lens
- Magnifies between F and the centre of the lens
- Lasers
- A device that amplifies light to produce a very narrow and intense beam
- Can be made from solids, liquids or gases
- Uses in eye surgery
- Repairing damaged retinas
- Remove damaged cells by cutting, cauterising or burning tissue
- Optical fibres guide the laser beam to the correct area of the body
- The Eye
- Optic nerve
- Sends information to brain to interpret image
- Cornea
- Refracts most of light
- Pupil
- (Iris opening) Adjusts light intensity
- Lens
- Further refration onto retina
- Ciliary muscles
- Control shape of lens and therefore focus
- Normal vision
- Near point 25cm
- Far point infinity
- Eye defects
- Long sight (Hyperopia)
- Eyeball too short
- Image forms behind retina
- Unable to focus on near objects
- Short sight (Myopia)
- Eyeball too long
- Image forms in front of retina
- Unable to focus on distant objects
- Glasses
- Adjust light before entering the eye to allow it to focus correctly
- Made from convex lenses, concave lenses, or a combination of both
- Long sight (Hyperopia)
- Optic nerve
- Lenses
- Keeping Things Moving
- Electromagnets
- Uses
- On cranes for lifting iron and steel
- In circuit breakers
- In loudspeakers
- In electric bells
- When a current flows through a wire a magnetic field is produced around the wire
- Uses
- The motor effect
- When a wire (conductor) carrying a current is placed in an external magnetic field, the magnetic field formed around the wire interacts with this permanent magnetic field. This causes the wire to experience a force that makes it move.
- The wire will experience no force if it is parallel to the direction of the magnetic field
- Increase size of force on wire
- Increase size of current
- e.g. have more cells
- Increase strength of magnetic field
- e.g. stronger magnets
- Increase size of current
- Reverse direction of force on wire
- Reverse direction of the flow of current
- e.g. turn the cell around
- Reverse direction of magnetic field
- e.g. swap magnets around
- Reverse direction of the flow of current
- Split ring commutator
- Reverses the flow of the current every half turn
- Allows the wire to keep spinning rather than just 'wobble' in the same position
- Reverses the flow of the current every half turn
- Flemming's left-hand rule
- First Finger = magnetic Field
- seCond finger = Current
- thuMb = Movement
- When a wire (conductor) carrying a current is placed in an external magnetic field, the magnetic field formed around the wire interacts with this permanent magnetic field. This causes the wire to experience a force that makes it move.
- Electromagnetic Induction
- Used by bicycle dynamos and generators to produce electricity
- If a conducting wire/coil of wires is moved through a magnetic field, a potential difference is induced across the ends of the wire
- An electrical current will be induced if the coil of wire forms a complete circuit
- The same effect occurs if the coil is stationary and the magnetic field moves
- Increase potential difference:
- Increase speed of movement of magnet/coils
- Increase strength of magnetic field
- Increase number of turns on the coil
- Transformers
- An alternating current is supplied to the primary coil
- This produces an alternating magnetic field in the iron core
- This magnetic field links with the secondary coil
- An alternating potential difference is induced across the ends of the secondary couil
- This magnetic field links with the secondary coil
- This produces an alternating magnetic field in the iron core
- Switch mode transformers
- Smaller and lighter
- Much higher frequency
- 50-200 kHz
- Operate on 50 Hz mains supply
- Use very little power when switched on and no load is applied
- e.g.
- Mobile phones
- Digital cameras
- Laptops
- Never truly efficient as energy is lost as heat to the surroundings
- Step up
- More turns on secondary coil
- Greater p.d on secondary coil
- Step down
- Less turns on secondary coil
- Lesser p.d across secondary coil
- Used in national grid to ensure efficent transmission of electricity
- Step up
- More turns on secondary coil
- Greater p.d on secondary coil
- Step up
- An alternating current is supplied to the primary coil
- Electromagnets
- Using Physics to Make Things Work
- Hydraulic Systems
- Pressure in a liquid is transmitted equally in all directions
- Liquids are virtually incompressible
- Gases compress, so are not suitable for hydraulics
- Different cross-sectional areas of pistons allow them to be used as force multipliers in hydraulics
- e.g. hydraulic jacks, car breaking, mechanical diggers
- Pressure
- The force acting over a particular surface area
- A small area results in a larger pressure than a big area when the force is the same
- 1 N/m^2 = 1 Pa
- Pendulums
- A mass at the end of a string that swings back and forth
- Frequency = number of times a pendulum swings backwards and forwards in 1 second
- Time period = time for one complete swing
- The time period only depends on the length of the pendulum
- Stability
- An object will topple if the line of action of the force, e.g. its weight lies outside its base
- The weight of the object causes a turning effect which makes the object topple
- Increasing stability
- Lower centre of mass
- Increase the width of the base
- An object will topple if the line of action of the force, e.g. its weight lies outside its base
- Centre of Mass
- The point of an object where the whole mass of the object is considered to be concentrated
- Found where lines of symmetry meet on regular shapes
- Can be found with a plumb line for irregular shapes
- A suspended object will come to rest with its centre of mass directly below the point of suspension
- Moments
- The turning effect of a force around a pivot point
- D= perpendicular distance between the line of action of the force and the pivot
- Increase size of moment
- Increase force
- Increase distance
- When an object isn't turning, the clockwise and anticlockwise moments are balanced.
- f1 x d1 = f2 x d2
- Levers use moments to act as force multipliers
- Centripetal Force
- An object moving at a constant speed in a circular path is continuously accelerating towards the centre of the circle
- Constantly changing direction when moving in a circular path means a changing velocity, and acceleration must be changing as acceleration is the rate of change of velocity
- Resultant foce causing this acceleration is the centripetal force
- This acts towards the centre of the circle
- Resultant foce causing this acceleration is the centripetal force
- Constantly changing direction when moving in a circular path means a changing velocity, and acceleration must be changing as acceleration is the rate of change of velocity
- Increase centripetal force
- Increase mass of object
- Increase speed of object
- Decrease radius of circle
- An object moving at a constant speed in a circular path is continuously accelerating towards the centre of the circle
- Hydraulic Systems
- Medical Applications of Physics
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