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X-rays
P3.1 Medical scanning
P3.2.1-2 Centre of mass and moments
Ultrasound

Short wavelength

Ionising

EM wave (transverse)

Affect a photographic film in the same

way as light
Absorbed by metal and bone

Transmitted by soft tissue

Wavelength roughly same size as an atom
 Partially reflected when they
meet a boundary between

Examples include CT scans (3D X-ray),
bone fractures, dentalproblems and
 Examples include pre-natal
Centre of mass
-the point at which the mass can be thought
 High frequency sound waves
(longitudinal)
to be concentrated
 Above upper limit of human
hearing (human hearing
T=
killing cancer cells
s = v x t
scanning and the removalof
kidney stones
pendulum.
v = speed (m/s)
M=F×d
t = time (s)
Moment (Nm) = force (N) x perpendicular distance from pivot (m)
to halve the
time to just
and 1 bundle for lighting)
Lasers – Used for cutting, cauterising
distance to
and burning e.g. in eye surgery
outside base there is a resultant
moment, object will topple
of motion (velocity) but not its speed.
P3.1 Refraction, lenses and the eye
Centripetal force always acts towards centre of the circle.
Centripetal force needed increases as:
passes from one medium to another. A lens forms an image by refracting light.
i = angle of incidence, r = angle of refraction 𝒓𝒆𝒇𝒓𝒂𝒄𝒕𝒊𝒗𝒆
𝒊𝒏𝒅𝒆𝒙 =
𝐬𝐢𝐧 𝒊
𝐬𝐢𝐧 𝒓
Diverging lens (concave)

Mass increases

Speed increases

Radius decreases
Triple physics (P3)
Refraction-the change of direction of light as it
Induction

P3.3.2 Transformers
If a conductor ‘cuts’ magnetic field lines, p.d.
induced across conductor (current flows).

If a magnet is moved into a coil of wire, p.d.
induced across coil.
Alternating current in
primary coil
Changing magnetic field
Applications:
-
Magnifying glass
-
Camera
The eye
-
Correction of long sight (eye ball too short)
The eye
The structure of the eye is limited to:
■retina
■lens
■cornea
in iron core
Applications:
-
Correction of short sight (eye ball
𝟏
𝒇
Positive for converging
𝑷 (𝑫, 𝒅𝒊𝒐𝒑𝒕𝒓𝒆𝒔) =
Negative for diverging
■pupil /iris
■ciliary muscle
■suspensory ligaments
Range of vision (focus): 25cm – infinity
Total internal reflection and critical angle
𝟏
𝒓𝒆𝒇𝒓𝒂𝒄𝒕𝒊𝒗𝒆 𝒊𝒏𝒅𝒆𝒙 =
𝐬𝐢𝐧 𝒄
Induces alternating p.d.
too long)
Lens power
Describing images
Real – constructed or formed
from real light rays
Virtual – constructed or formed
from virtual/imaginary rays
Upright/inverted – right way
up/upside down
Magnified/ diminished – bigger
or smaller
𝒊𝒎𝒂𝒈𝒆 𝒉𝒆𝒊𝒈𝒉𝒕
𝒎𝒂𝒈𝒏𝒊𝒇𝒊𝒄𝒂𝒕𝒊𝒐𝒏 =
𝒐𝒃𝒋𝒆𝒄𝒕 𝒉𝒆𝒊𝒈𝒉𝒕
a
Centripetal force
-the resultant force causing this acceleration.
Load > Force
the boundary
Converging lens (convex)
the centre of the circle. This changes the objects direction
Levers
Levers act as force multipliers
find the
v
Objects moving in circles continuously accelerate towards
For objects not turning (balanced):
Total clockwise moment = total anticlockwise moment
you might have
Contain optical fibres (1 bundle for image
P3.2.4 Circular motion
Stability
-if the line of action of weight is
s = distance to boundary (m)
*remember
𝐹1 𝐹2
𝐴2
=
→
𝐹2 =
𝐹1
→
𝐹2 > 𝐹1
𝐴1 𝐴2
𝐴1
Hydraulics with different areas (e.g. A1 and A2) act as force multipliers.
Time period depends on the length of the
Moments
-the turning effect of a force
Endoscopes–
Use total internal reflection for imaging.
F
A
Pressure (Pa) = force (N) ÷ area (m2)
1
𝑓
Time period (s) = 1 / frequency (Hz)
two different media
directions.
P=
Pendulums
20Hz-20 000Hz)
P3.2.3 Hydraulics
Liquidsare virtually incompressible, so the pressure is transmitted equally in all
across secondary coil
Step-up increase p.d. (more turns on secondary coil)
Step-down decrease p.d. (fewer turns on secondary coil)
𝑽𝑷 𝒏 𝑷
=
𝑽𝑺 𝒏 𝑺
V = potential difference (V)
n = number of turns in coil
I = current (A)
P = power (W)
If transformer is 100% efficient PP = PS so
IPVP = ISVS.
Switch mode transformers

High frequency (50kHz – 200kHz)

Lighter and smaller than normal transformers


So they are useful for mobile phone chargers etc.
Use very little power when no load applied
P3.3.1 Motor effect and electromagnets
-When a current flows through a wire a
magnetic field is produced around the wire.
Motor effect
If current carrying wire ‘cuts’
through field lines,
experiences a force.
Size of force increases with:


Larger current
Stronger magnetic field
No force if current parallel
to field lines.
Electromagnets
When current carrying
wire coiled around iron,
produces an
electromagnet.
Applications

Scrapyard cranes


RCCB
Bell
Fleming’s left hand rule
Force is reversed if current or
magnetic field changes direction.