P3 Revision Notes

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  • Created by: Rupesh
  • Created on: 27-04-13 13:53
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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 = speed
o t = time taken
Uses:
Ultrasound waves are used in prenatal scanning.
Ultrasound waves are also used to break down kidney stones.
Difference between Ultrasound waves and X-rays:
They are non-ionising.
They produce an accurate image of soft tissue
X-Rays:
X-rays have a short wavelength. The wavelength is the same as the diameter of its atom.
Cause ionisation.
Affect photographic film in the same way light does.
X-rays are absorbed by metal and bone.
CT Scans:
A CT Scan can give provide an image from any direction.
It is connected to a CCD (Charged Couple Device) which is used to convert the x-rays into light so that a
digital image on the screen is created.
Benefits:
3D image produced.
It can also differentiate between harder and softer tissue.
Safety Issues:
Lead Shielding ­ Lead absorbs x-rays
Film Badges ­ used to see the amount of x-ray the person wearing the badge has been exposed to

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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:…read more

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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 film or CCD Image focused on retina…read more

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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.…read more

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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…read more

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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 object.
Refractive Index:
Refraction is the changing of direction of light when it travels from one medium to another.…read more

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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 material of the lens
Higher:
For a given focal length, the greater the refractive index, the flatter the lens. The lens can be made
thinner.…read more

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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 suspension.…read more

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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 moment hence,
the object will topple over.…read more

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

Comments

Ben Fenton

Shame there is nothing on EM induction and Transformers but cheers anyway Rupesh!

trying4law

Could be a bit more detailed; hydraulics and the motor effect lacked a lot of detail (and they're the things I get stuck on) and obviously there isnt' anything on EM induction and Transformers, although I could just write those notes myself. Other then that, very good! (liked how you used some diagrams from the MyGCSEScience channel on youtube)

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