# P3 Revision Notes

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• Created by: Rupesh
• Created on: 27-04-13 13:53
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## Pages in this set

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P3:

Ultrasound:

The frequency is the number of vibrations per second.
The lowest frequency for humans is 20 Hz and the highest is 20,000 Hz.
Any sound that has a frequency higher than 20,000 Hz is called Ultrasound.
s = v x t; whereby:
o s = distance
o v…

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Comparison between CT Scanners and X-ray machines:

CT Scanners: X-ray Machines:

Higher Dose Lower dose

3D Image 2D Image

Distinguish between different soft tissues Cannot distinguish different soft tissues

Expensive Cheaper

The Eye:

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Ray diagrams for people who are either short sighted or long sighted:

How lensed are used to correct either short sight or long sight:

Camera: Eye:

Converging lens fixed focus Converging lens variable focus

Focus achieved by varying lens position Focus achieved by contraction of ciliary muscle

Image focused on…

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Brightness controlled by apeture and diaphragm Brightness controlled by iris and the pupil

NB: Both the eye and the camera produce a REAL, INVERTED and DIMINISHED image.

Lenses:

There are 2 types of lenses:
o Concave
o Convex

Ways in which the different types of lenses can be drawn:

Concave…

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Object is before the principal focus and the lens

Convex Lenses:

2 scenarios drawing ray diagrams for formation of images using convex lenses:

Scenario 1:

The object is between the principal focus and the lens

Scenario 2:

The object is behind the principal focus and the lens

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Magnification = Image Height
Object Height

NB:

A virtual image is formed when virtual/imaginary light rays cross and when the image is on
the same side of the object.
A real image is formed when real light rays cross and when the image is on the opposite
side of the…

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Focal length and lens power:

Power of lens (Dioptres, D) = _ 1 = 1
focal length (metres) f

NB: For a concave lens, the value of the lens power will always be negative.

Factors that affect the lens focal length:
o Curvature/Thickness of lens
o Refractive Index of the…

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Cutting

Burning

Laser eye surgery ­ burn away a very thin layer of the lens

Centre of Mass:

The centre of mass of an object is the point at which the mass of an object may be thought to be
concentrated.
Centre of mass is directly below the point of…

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Moment (Nm) = Force (N) X Perpendicular Distance from the line of action of the force to the
pivot (m).
M=FXd
Higher Tier:
o Clockwise moments = Anti-clockwise moments

Higher Tier:

Balanced Objects:

If the line of action of the weight lies outside the base there will be a resulting…

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Armature attracted
Second circuit swithced on
A low current circuit switches on a high current circuit.

The Motor Effect:

The force can be increased by:
o Increasing the current
o Increasing the magnetic field
The force can be reversed by:
o Reversing the magnetic field
o Reversing the current