Transcript (V) I - Hartismere

OCR Gateway P4-6
A-A* Evaluate
Justify
Recommend
Judge
B-A
Interpret
Apply ideas
& design
models
Solve
problems
Synthesise
C-B
Describe
processes
Explain –
why & how
D-C
Describe
Compare
observations similarities
Compare
differences
Classify
E-D
Name
State
Label
Recall
Analyse
patterns &
draw
conclusions
Use abstract
ideas
How to revise
Mind-maps
Post-it notes
Diagrams
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Prepare and practice
No. of marks / No rushing / No gaps
‘Explain why’ – cause and effect
‘Calculate’ – formula, substitute ... unit
‘Justify’ – Give reasoned arguments
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Boost your brain cells
Equipment & get ready
Sleep and breakfast
Technique & don’t panic
P4: Radiation For Life
a Sparks
b Uses of electrostatics
c Safe electricals
d Ultrasound
e What is radioactivity?
f Uses of radioisotopes
g Treatment
h Fission and fusion
P4a Sparks
Electrostatics
Van de Graaff:
friction moving
electrons
Rubbing transfers
electrons
Electrons are negative
Shock when
electrons go
through you
Danger of
explosions
The Law of Charges:
Like charges repel, unlike charges attract
If atoms gain/lose electrons: +/– ions

Safety:
• appliances with metal case are earthed
• bonding fuel tankers to aircraft
P4b Uses of electrostatics
• Electrostatic precipitator
• Spray painting
Negative
paint
Positive
surface
• Defibrillator
P4c Safe electricals
Long-thin wires:
- more resistance
- less current
Resistance = voltage V
in ohms W current A
OHM
Power = voltage x current
W (J/s)
V
A
Live
brown (high voltage)
Neutral blue (completes circuit)
Earth green & yellow
VOLT
AMP
If case becomes live current goes to earth.
Double insulated cases don’t conduct so have no earth.
Fuses melt & blow if too much current and prevents fire
from flex/appliance overheating – must be replaced.
Circuit breakers trip if too much current – switch it back on.
P4d Ultrasound
Loudness ~ amplitude
Pitch ~ frequency
- transverse (like light)
Amplitude
Wavelength λ
- longitudinal (like sound)
Compression – high pressure
Rarefaction – low pressure
Ultrasound > 20 000 Hz
higher frequencies than you hear
Uses: Body scans – reflections off deeper layers take a longer time.
Speed of blood flow. Breaking down kidney stones.
P4e What is radioactivity?
parent daughter
Radiation from an
unstable nucleus
that ionise atoms:
a:
2p,2n (too + !)
(as helium nucleus)
b:
g:
fast electron
(n
p + e)
The average time for
Equations:
Alpha:
e-m wave
the number of nuclei
of an isotope in a
sample to halve.
Beta:
HT
Mass no. = p + n no.
Atomic no. = p no.
Half life
Number of half lives
Uses:
Background
radiation:
mainly from rocks
& cosmic rays
g tracers in pipes - detect less activity after leak/blockage
Smoke alarm - less ionisation/current if a hits smoke particle
Dating rocks - as uranium decays, lower uranium/lead ratio
HT C-14 dating – C-14 ratio in dead/living matter less with time
P4g Treatment
Radioisotopes made if
nuclei absorb neutrons
in nuclear reactors
Hazards
HT
Tracers: g (or b)
- sterilising equipment
half life
light
micro/radio
-UV
tracers for
diagnosisIR - short
- eat/drink/inject
- to kills cancer cells
- time to spread
- detect/display
non-ionising
Uses of gamma:
gamma X-rays
fast electrons
ionising
HT
X-rays
Radiotherapy:
- wide g beam
- focus on tumour
- rotate round
- so limit damage
P4h Fission and fusion
Nuclear fission:
- splitting U
Chain
reaction
n
235 U
92
Rods
absorbFusion:
neutrons
Nuclear
and stop the reaction
- joining nuclei
bombing out of control
HT
In stars
& H-bombs:
needs high
temperature
and pressure
International
joint venture
to engineer
fusion power
Danger of
radioactive waste
Is cold fusion possible?
P5: Space For Reflection
a Satellites, gravity and circular motion
b Vectors and equations of motion
c Projectile motion
d Action and reaction
e Satellite communication
f Nature of waves
g Refraction of waves
h Optics
P5a Satellites, gravity
and circular motion
F
gravity provides
centripetal force
F
Earth
Moon
artificial
satellite
HT
Sun
Elliptical orbit
fast near Sun
as force α 1/r2
Weather satellite
in low polar orbit
in geostationary orbit
24 hours above equator
(for ‘Sky’ communication)
Comet
GPS - in 12h orbits
P5b Vectors & equations of motion
resultant
resistive
forces
vector
quantity
has
direction
eg. force
velocity
scalar
quantity
no
direction
eg. mass
time
a
HT Pythagoras
2
2
2
c a =b +c
b
a  b2  c2
Velocity (m/s)
thrust
gradient (m/s2) = acceleration
v–u
a
=
v
t
½at2
v = u + at
m/s
area (m)
= distance
s
u
no s
+
HT
ut
t
s = ut + ½at2
no v
Time (s)
KS3
distance
speed x time
KS4
av. speed
s = ½(u+v)t
no a
HT
v2 = u2 + 2as
no t
P5c Projectile motion
constant velocity
1
4
9
x = ut
parabolic
trajectory
force due
to gravity
16
ignoring air
resistance
25
y = ½ at2
Maximum
range at 45o
P5d Action and reaction
Newton’s third law: Every action has an equal and opposite reaction.
A FB
= – BFA
The book & Earth interact
(via the force of gravity)
A book in the air ?
In collisions/explosions the two bodies interact
A pulls/pushes B and B pulls/pushes A
Momentum is conserved
total momentum before
= total momentum after
When cars collide
m1u1 + m2u2 = (m1+m2)v
HT
At high temperature, particles exert high pressure
as particles faster, collisions harder & more often
Rocket propulsion
- forward recoil
as exhaust gases
explode backwards
kg m/s
units:
HT
momentum = mass x velocity
A book on a table
P5e Satellite communication
ionosphere
noise removed
noise
analogue
digital
Radio
< 30MHz
(long λ)
reflect off
ionosphere
(long range)
diffract
round
objects
Micro
< 30GHz
penetrate
atmosphere
high orbit
high freq
Waves
> 30GHz
(short λ)
absorbed or
scattered by
rain or dust
short
range
Diffraction D > λ limits
spreading out
D≈λ
diffraction
- so exact
alignment
of dishes
needed
HT
P5f Nature of waves
Interference
Constructive
in phase
Destructive
½ λ out of step
Coherent:
- same freq.
- in phase
- same amp.
λ
HT
Reflected light is
partly polarised
Transverse waves
can be polarised
Particle theory cannot explain interference. Wave theory can.
Refraction
P5g Refraction of waves
refraction
critical angle
total internal
reflection
Refractive index
speed in vacuum
air
= speed in glass
glass
300 Mm/s
=
= 1.5
200 Mm/s
Dispersion
white
Uses of TIR:
-
optical fibres
-
road signs
-
binoculars
blue light
slower
than red
Blue light has a greater
refractive index than red HT
long λ
spectrum
P5h Optics
parallel
Convex (converging) lenses
F
thinner lens
has longer
focal length
principal axis
focal length
optical
centre
focal
point
Uses of a convex lens:
Cameras
- Projectors
-
-
real image
on screen
object
Magnifying glass
virtual image
optical illusion
image height
=
Magnification object height
image
P6: Electricity For Gadgets
a Resisting
b Sharing
c It’s logical
d Even more logical
e Motoring
f Generating
g Transforming
h Charging
P6a Resisting
Ohm’s Law
A
VR
Voltage V (V)
battery
Electrons
collide
with ions
Current I (mA)
Filament lamp
V (V)
rheostat
Longer resistance wire
- less current flows
- so dimmer bulb
Rope model
Resistance (W) = voltage (V)
current (A)
As current increases
- temperature increases
- so atomic vibrations
I (A) inhibit the flow of electrons
- resistance increases
- gradient of V/I increases
P6b Sharing
R1
V1
Vin
R2
Resistors in series R1 V1
=
= potential dividers R2 V2
If Vin = 3V, R1 = 8Ω & R2 = 4Ω
V2
V1 = 2V & V2 = 1V
Total in series
RT = R1 + R2
Changing the resistance
of a VR, LDR or thermistor
changes the pd across it
In less light, the LDR resists more
& has more voltage across it
In parallel
- currents add up
- more current flows
- total R decreases
A
HT
If R2 ⋙ R1
V2 ≈ Vin & V1 ≈ 0V
R
Vin = V↑ + V↓
V
V
6A = 2A + 4A
R1
A
A
R2
V
V
Total in parallel
1
1
1
=
+
HT
RT R1 R2
P6c It’s logical
Transistor:
9V
safety
resistor
Truth tables
electronic switch
Logic Gates
led
NOT
AND
0V
+6V
micro-technology
A
A small base current
triggers current thro
collector & emitter
B
Ie = Ib + Ic
5V hi 1
AND
gate
out
0V
0V lo 0
A B
OR
car courtesy light
out
0
0
0
0
1
0
1
0
0
1
1
1
NAND
NOR
HT
P6d Even more logical
HT
Combining logic gates
hot 1 cold 0
humid 1 dry 0
A B C D
out
0
0 0 0 1
0
0 1 1 1
1
1 0 1 1
1
1 1 1 1
1
VR
thermistor
0
0V
C
D
switch on 1 off 0
relay
to fan
If it is hot OR humid
AND the switch is on
air conditioning starts
relay
If temperature is hot so
the thermistor has low R
or if the VR has high R
the output voltage is high
The variable resistor will adjust
the temperature at which
the output voltage goes high.
HT
Mains power would damage
transistors or logic gates.
The relay isolates the circuits.
normally open
common
normally closed
relay – to switch on/off
a high power mains circuit
from a low power logic circuit
HT
P6e Motoring
–
HT
current I
current
First finger = Field
field
magnetic
field
Fleming’s
LHR
SeCond
Finger =
Current
motion
ThuMb = Motion
Motor
Effect
+
B
solenoid
kinetic
useful work
Faster if more
- current
- coils
- mag. field
electrical
I
heat
Commutator
to reverse current
every half revolution
HT
P6f Generating
50Hz a.c.
Electromagnetic
Induction
Motor
higher
frequency
Electric
Kinetic
Generator
magnet
More voltage if:
- faster speed
- stronger field
- more coils
coil
coil
‘cuts’
field
faster
slip rings
brushes
Electricity
can be
transmitted
& stored
P6g Transforming
Changing primary current, changes magnetic field in core,
induces voltage across secondary coil.
iron core
primary
coil
secondary
coil
Ratios
Vp
Vs

HT
Np
Ns
Work on ac not dc
Used in:
phone chargers
shaver sockets
etc.
P6g Transforming cont.
Power loss = current 2 x resistance
HT
If current half, power loss a quarter
Transformers are nearly 100% efficient
∴ power to primary = power from secondary
Vp x Ip = Vs x Is
if V more
∴
Vs Ip
=
Vp Is
Step-up
transformer
to grid
230V
Sub-Station
I less
132000V
Step-down
transformer
You step up
voltage to reduce
current & heat
loss in the cables
P6h Charging
half wave
rectified
HT
diodes conduct
only one way
Bridge circuit
full wave
rectification
current
diode
high R
low R
potential
difference
HT
hole electron
Capacitor
with a capacitor
charge
stored:
voltage
more
discharge:
voltage
less
time
HT
input
smoothed
output
like battery
The desire to succeed means
nothing without the will to prepare!