P3 Physics AQA 2012. What is likely to come up?. Expect a question on Centre of Mass as AQA usually put one on. The Eye was new in 2012, and eye structure was on 2013 paper. This year long/short sightedness or near vision?
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P3 Physics AQA 2012
A-scan. The peaks correspond to reflection from surfaces inside the body. Taller peak represent stronger reflections.
B-Scan. The transducer is moved across the body and the return signals are stored electronically.
The signal strength controls the brightness/colour of each part of the image displayed on a screen.
Blood vessels inside the eye
the angle of incidence = the angle of reflection.
Image is virtual, same size as object, same distance behind mirror as object is in front,
Upright and laterally inverted (back to front).
SPL: Alfred Pasieka
Air n ~ 1
Uses Total Internal Reflection
A bundle of fibres send the light into the dark cavity
A bundle of fibres receive the reflected light into a camera
Glass fibres are flexible and transmit/ receive images near the speed of light
+ve for converging lens, -ve for diverging lens.
Corbis V257 (NT)
Photo: S. Meltzer/Photolink/Photodisc 24 (NT)
Concave lenses are used to correct short sight. They always produce upright virtual images
Sclera – Tough inelastic outer coating.
Choroid – Vascular layer – Retina needs a rich blood supply.
Retina – Photosensitive layer.
Cornea – Main light-focussing structure. contributes ~2/3 refractive power of the eye.
Crystalline lens – Allows the eye to accommodate – adjust so that it is focussed on near objects.
Pupil – Like the aperture of a camera. Allows light to enter the eye. The Iris can dilate/constrict the pupil to adjust the size of the pupil.
Optic Nerve – The region where the optic nerve leaves the retina.
Fovea – Very highly concentration of cone cells at the centre of our
Simple Refractive errors
The sum of the anticlockwise moments about any point
the sum of the clockwise moments about that same point.
The period of a pendulum is the time for one complete swing.
The period of the pendulum T(sec) increases as the length increases. It is unaffected by the mass of the bob
The best way to determine the period is to time 10 complete swings and divide by10.
The frequency f of the swings = 1/ T and T = 1/ f
PRESSURE IN A FLUID IS THE SAME ALL THROUGH
P = F1 = F2
SO A SMALL FORCE ON A SMALL AREA GIVES A BIG FORCE ON A BIG AREA
Pressure at large piston due to load = 15000
The pressure at the small piston must also = 75N/cm2
For small piston, P =F/A, then F = PxA = 75x3 = 225N
– the mass of the object increases,
– the speed of the object increases,
– the radius of the circle decreases.
The car is travelling at a steady speed but the direction is always changing – so the velocity is changing. Acceleration is the change of velocity per sec - so the car is accelerating. The friction between the tyres and the road provide the centrepetal force to keep the car travelling in a circular path.
The three fingers are mutually perpendicular.
Point the relevant fingers in the direction of the magnetic field (North – South)
And the electric current (+ to -)
First finger - Force
thuMb - Movement
seCond finger - Current
WHICH WAY WILL THE WIRE MOVE?
MAG FIELD ALWAYS N TO S
CURRENT ALWAYS + TO -
A wire carrying an electrical current that is inside a magnetic field experiences a force.
SPL: R. Maisonneuve, Publiphoto Diffusion
p.d. across primary, VP number of turns on primary, NP
p.d. across secondary, VS number of turns on secondary, NS
Use the transformer equation:
A transformer is used to step a p.d. of 230 V down to 10 V. The secondary coil has 60 turns. How many turns are there in the primary coil?
VP = 230 V, VS = 10 V, NS = 60 turns
= 1380 turns