1. OCR Gateway P4-6

2. A-A*EvaluateJustifyRecommendJudge B-AInterpret Apply ideas & design models Solve problems Synthesise C-B Describe processes Explain – why & how Analyse patterns & draw conclusions Use abstract ideas D-C Describe observations Compare similarities Compare differences Classify E-DNameRecallStateLabel

3. How to revise Prepare and practice No. of marks / No rushing / No gaps ‘Explain why’ – cause and effect ‘Calculate’ – formula, substitute... unit ‘Justify’ – Give reasoned arguments Mind-maps Post-it notes Diagrams Revision cards Quiz sharing Highlighting Discussing Ask questions Others test you Boost your brain cells Equipment & get ready Sleep and breakfast Technique & don’t panic

4. 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

5. Van de Graaff: friction moving electrons Van de Graaff: friction moving electrons Rubbing transfers electrons Electrons are negative The Law of Charges: Like charges repel, unlike charges attract Electrostatics P4a Sparks If atoms gain/lose electrons: +/– ions Shock when electrons go through you Danger of explosions Safety: appliances with metal case are earthed bonding fuel tankers to aircraft

6. P4b Uses of electrostatics Electrostatic precipitatorSpray painting Defibrillator Negative paint Positive surface

7. P4c Safe electricals earth If case becomes live current goes to earth. Fuses Fuses melt & blow if too much current and prevents fire from flex/appliance overheating – must be replaced. Circuit breakers Circuit breakers trip if too much current – switch it back on. Live brown (high voltage) Neutral blue(completes circuit) Earth green & yellow Power = voltage x current W (J/s) V A Resistance = in ohms  voltage V current A Long-thin wires: - more resistance - less current Double insulated cases Double insulated cases don’t conduct so have no earth.

8. Amplitude Wavelength λ - transverse (like light) - longitudinal (like sound) Loudness ~ amplitude Pitch ~ frequency P4d Ultrasound 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. Unlike X-rays, no damage to living cells

9. parent daughter Activity of source Number of half lives The average time for the number of nuclei of an isotope in a sample to halve. Half life Radiation from an unstable nucleus that ionise atoms:  : 2p,2n (too + !) (as helium nucleus)  : fast electron (n p + e)   : e-m wave P4e What is radioactivity? Mass no. = p + n no. Atomic no. = p no. Equations: HT Alpha: Beta:

10. Background  radiation:  mainly from rocks  & cosmic rays Uses:   tracers in pipes - detect less activity after leak/blockage Smoke alarm - less ionisation/current if   hits smoke particle Dating rocks - as uranium decays, lower uranium/lead ratio C-14 dating – C-14 ratio in dead/living matter less with time HT

11. P4g Treatment gamma X-rays UV light IR micro/radio ionising non-ionising X-rays HT fast electrons Radioisotopes made if nuclei absorb neutrons in nuclear reactors Uses of gamma: - sterilising equipment - tracers for diagnosis - to kills cancer cells HT Tracers:   (or  )  - short half life - eat/drink/inject - time to spread - detect/display Hazards Radiotherapy: - wide  beam - focus on tumour - rotate round - so limit damage

12. P4h Fission and fusion Nuclear fission: - splitting U n U 235 92 Chain reaction Chain reaction Danger of radioactive waste Rods absorb neutrons and stop the reaction bombing out of control Nuclear Fusion: - joining nuclei HT In stars & H-bombs: needs high temperature and pressure International joint venture to engineer fusion power Is cold fusion possible?

13. 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

14. P5a Satellites, gravity and circular motion F F gravity provides centripetal force MoonEarth artificial satellite in geostationary orbit 24 hours above equator (for ‘Sky’ communication) Sun Comet Elliptical orbit fast near Sun as force α 1/r 2 HT Weather satellite in low polar orbit GPS - in 12h orbits

15. s gradient (m/s 2 ) = acceleration Velocity (m/s) Time (s) area (m) = distance + m/s s = ½ (u + v) t av. speed v = u + at no a a = v – u t no s P5b Vectors & equations of motion resistive forces thrust resultant vector quantity has direction eg. force velocity scalar quantity no direction eg. mass time a b c a 2 = b 2 + c 2 HT Pythagoras KS3 distance speed x time KS4 v u t HT ut ½ at 2 s = ut + ½ at 2 no v HT v 2 = u 2 + 2as no t

16. constant velocity y = ½ a t 2 constant acceleration 1 4 9 16 25 x = u t P5c Projectile motion parabolic trajectory ignoring air resistance force due to gravity Maximum range at 45 o

17. Newton’s third law: Every action has an equal and opposite reaction. A book on a tableA book in the air ? A F B = – B F A The book & Earth interact (via the force of gravity) In collisions/explosions the two bodies interact A pulls/pushes B and B pulls/pushes A P5d Action and reaction momentum = mass x velocity HT units: kg m/s Rocket propulsion - forward recoil as exhaust gases explode backwards Momentum is conserved total momentum before = total momentum after When cars collide m 1 u 1 + m 2 u 2 = (m 1 + m 2 )v HT At high temperature, particles exert high pressure as particles faster, collisions harder & more often

18. P5e Satellite communication ionosphere 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 spreading out HT D > λ limits diffraction - so exact alignment of dishes needed noise analogue D ≈ λD ≈ λ digital noise removed

19. P5f Nature of waves Transverse waves can be polarised Refraction Interference Constructive Destructive in phase ½ λ out of step λ Coherent: - same freq. - in phase - same amp. Particle theory cannot explain interference. Wave theory can. HT Reflected light is partly polarised

20. P5g Refraction of waves white spectrum Dispersion long λ blue light slower than red Blue light has a greater refractive index than red HT air glass refraction critical angle total internal reflection Uses of TIR: - optical fibres - road signs - binoculars Refractive index = == 1.5 speed in vacuum speed in glass 300 Mm/s 200 Mm/s

21. P5h Optics image Magnification image height object height = Convex (converging) lenses principal axis optical centre focal point F thinner lens has longer focal length focal length parallel object Uses of a convex lens: - Cameras - Projectors - Magnifying glass real image on screen virtual image optical illusion

22. P6: Electricity For Gadgets a Resisting b Sharing c It’s logical d Even more logical e Motoring f Generating g Transforming h Charging

23. P6a Resisting A VR rheostat battery Rope model Longer resistance wire - less current flows - so dimmer bulb Voltage V (V) Current I (mA) resistance = gradient Resistance (  = voltage (V) current (A) Ohm’s Law Electrons collide with ions Filament lamp V (V) I (A) As current increases - temperature increases - so atomic vibrations inhibit the flow of electrons - resistance increases - gradient of V/I increases

24. Changing the resistance of a VR, LDR or thermistor changes the pd across it R In less light, the LDR resists more & has more voltage across it V V V V V in = V + V R1R2 R1R2 V1 V1 V2V2 V in P6b Sharing Resistors in series = potential dividers R 1 V 1 R 2 V 2 = If V in = 3V, R 1 = 8Ω & R 2 = 4Ω V 1 = 2V & V 2 = 1V If R 2 ⋙ R 1 V 2 ≈ V in & V 1 ≈ 0V Total in series R T = R 1 + R 2 A A A R 1 R 2 In parallel - currents add up - more current flows - total R decreases Total in parallel 1 1 1 R T R 1 R 2 = + HT ↑↓ 6A = 2A + 4A

25. P6c It’s logical Transistor: electronic switch A small base current triggers current thro collector & emitter I e = I b + I c micro-technology 9V 0V safety resistor +6V A B out 0V AND gate ABout 000 010 100 111 led Logic Gates NOT AND OR NAND NOR car courtesy light HT 5V hi 10V lo 0 Truth tables

26. P6d Even more logical CDCD Combining logic gates hot 1 cold 0 humid 1 dry 0 switch on 1 off 0 relay to fan If it is hot OR humid AND the switch is on air conditioning starts ABCDout 00 00010 01111 10111 11111 VR thermistor 0V If temperature is hot so the thermistor has low R or if the VR has high R the output voltage is high relay – to switch on/off a high power mains circuit from a low power logic circuit HT normally open common normally closed relay 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. HT

27. P6e Motoring solenoid B I ThuMb = Motion First finger = Field SeCond Finger = Current Fleming’s LHR current field motion HT current I magnetic field – +– + Motor Effect useful work wasted electrical kinetic heat Faster if more - current - coils - mag. field HT Commutator to reverse current every half revolution

28. 50Hz a.c. P6f Generating Electromagnetic Induction magnet coil slip rings brushes coil ‘cuts’ field faster More voltage if: - faster speed - stronger field - more coils Generator Motor ElectricKinetic Electricity can be transmitted & stored higher frequency

29. Ratios iron core primary secondary coil coil Changing primary current, changes magnetic field in core, induces voltage across secondary coil. P6g Transforming Work on ac not dc Used in: phone chargers shaver sockets etc. HT

30. The National Grid Sub-Station 132 000 V 230V Step-down transformer You step up voltage to reduce current & heat loss in the cables Step-up transformer to grid P6g Transforming cont. Power loss = current 2 x resistance If current half, power loss a quarter Transformers are nearly 100% efficient ∴ power to primary = power from secondary V p x I p = V s x I s V s I p V p I s ∴ = if V moreI less HT

31. P6h Charging Bridge circuit full wave rectification diode diodes conduct only one way half wave rectified current potential difference high R low R hole electron input Capacitor time charge stored: voltage more discharge: voltage less smoothed output like battery with a capacitor HT

32. The desire to succeed means nothing without the will to prepare!