AN ROINN OIDEACHAIS AGUS EOLAÍOCHTA

Transcription

1 AN ROINN OIDEACHAIS AGUS EOLAÍOCHTA Leaving Certificate Examinations 00 Physics Higher Level Marking scheme

2 In considering this marking scheme the following points should be noted: 1. In many instances only key words are given, words that must appear in the correct context in the candidate s answer in order to merit the assigned marks.. Words, expressions or statements separated by a solidus, /, are alternatives which are equally acceptable.. Answers that are separated by a double solidus, //, are answers which are mutually exclusive. A partial answer from one side of the // may not be taken in conjunction with a partial answer from the other side.. The descriptions, methods and definitions in the scheme are not exhaustive and alternative valid answers are acceptable. 5. The detail required in any answer is determined by the context and manner in which the question is asked and by the number of marks assigned to the answer in the examination paper. Therefore, in any instance, it may vary from year to year. 6. For lack of units, or incorrect units, one mark is deducted, as indicated. This is shown as (-1), or (-1) etc., in the right hand column. 7. Each time an arithmetical slip occurs in a calculation one mark is deducted. This is shown as (-1), or (-1) etc., in the right hand column.

3 Section A 10 Marks Marks awarded for the THREE best answers Question 1 Calculate the sum of..forces.. up = + = 6 (N) down = = 6 (N) resultant force /vector sum = 0 / forces up = forces down ( If weight of metre stick is omitted, give a maximum of 6/9 ) Calculate the sum of..moments.. moment = force distance (stated or implied) sum of anticlockwise moments = (+).8 (N m) / 80 (N cm) sum of clockwise moments =.797 ( or.8) (N) (+) / sum of moments is zero / sum of clockwise = anticlockwise / law verified (Deduct marks if moments are taken about a point other than the 10 cm mark) Describe how the centre of gravity balance metre stick on a suitable fulcrum read / mark position of equilibrium Why is it.. vertically spring balance gives correct reading / friction or additional forces / distance along metre stick = perpendicular distance / distance can be read directly / reference to Cos ϑ or Sin ϑ 7

4 Question Advantage of room temperature heat lost to surroundings heat gained approximately equal Describe how mass of ice is found final mass (of calorimeter + contents) initial mass of calorimeter + water subtract Calculate c ( mc ϑ) Al + ( mc ϑ) water = ( ml) ice + ( mc ϑ) melted 6 ice (ml missing 0; any other missing item - ) fall in temperature = 16. o C substitution into formula containing ml J kg -1 Two reasons why answer is not exact thermometer not sensitive enough lack of insulation lack of stirring heat loss/gain to surroundings too long for ice to melt inside of calorimeter tarnished splashing heat capacity of thermometer any two, +

5 Question Describe with diagram fixed length of string and method of measuring tension tuning fork / signal generator and magnet find frequency and tension when resonance occurs change frequency and repeat ( - for lack of a diagram) Why was length kept constant? frequency varies with length / keep all other factors constant 6 (For f l give ) Plot a graph square root of tension / frequency squared label axes plot 6 points correctly straight line good fit (No graph paper maximum first ) Estimate tension ( T =) 5.5 to to.5 N 5

6 Question Diagram of apparatus variable power source and ammeter in series voltmeter in parallel electrodes in solution anode and cathode correctly labelled Draw graph axes labelled 6 points plotted correctly straight line good fit (No graph paper maximum first ) Calculate resistance two points on graph method for slope 19.5 to 0.5 Ω Sketch straight line starting at v > 0 6

7 Question 5 MARKS AWARDED FOR THE EIGHT BEST ANSWERS (a) v = rω 5 (rad) s -1 (b) t = T 7 7 (Any reference to Kelvin and 7 / specific example e.g 7 K = 0 o C ) 7 (c) Solar constant by time / kj /.7 10 J (d) change in frequency / pitch /wavelength movement (e) A P // rate at which sound energy passes / no. of watts explain // per unit area 1 (f) 00 6 / 5 10 m 7 1 (g) CV J (h) cutting off supply / current / power 7 ( fault / difference in current between live and neutral / safety / protects against electrocution / current in earth (wire) ) (i) magnetic flux density (B), Current (I), Length (l), angle any two + (j) splitting (large) nucleus release of energy / radiation / nuclei / neutrons 7

8 Question 6 State Newton s nd Law force is proportional rate of change of momentum ( F = ma explain symbols ) Name Law and give statement Hooke s restoring force (= to k times) // Extension displacement // force / load / weight Name and describe motion simple harmonic / SHM a = ω s // acceleration is α to explain // displacement / distance (and direction) other examples stretched elastic / pendulum, oscillating magnet, springs of car, vibrating tuning fork, object bobbing in water waves, ball in saucer, etc. or any system that obeys Hook s law any two, by Calculate k F = mg / / 588 (N) N m -1 Calculate(i) period k = ω m ω = 8 (s -1 ) T = Π ω 0.16 to 0.17 s T = π m k 7 substitution 0.16 to 0.17 s Calculate (ii) no. of oscillations (f =) T 1 6 (5.88 to 6.5) 8

9 Question 7 Explain the terms (i) constructive interference waves combine wave of greater amplitude Explain (ii) coherent same frequency / wavelength in phase / constant phase difference Condition for destructive interference out of phase / path difference // trough meets by (n +) 1 wavelength // crest / peak Wave nature of light diffraction grating / Young s slits // polaroids spectrometer and light source / laser // light source shine light through grating or slits // shine light, rotate one interference pattern // change in intencity (i) Calculateλ for radiowaves v = fλ 10 m / 10 km (ii) What is the minimum distance half wavelength / 5 km 1500 km + 5 km 1505 km (iii) Calculate minimum h Pythagoras theorem (any implication) substitution 61 km // m 5 9

10 Question 8 Define (i) power W rate // VI / / RI t of doing work / using energy // explain symbols (ii) resistivity RA resistance of a piece of material // l unit length and unit area // explain R, A and l Demonstration of heating effect apparatus circuit way of detecting heat change result Calculate (i) resistance A = πr / π ρl RA R = / ρ = A l Substitution 9.5 to 9.6 Ω (ii) current W = VI 00 A (iii) energy lost (P =) I R W / 0.8 MW Reducing energy lost thicker cables lower resistivity / resistance higher V (tension) EHT 5 10

11 Question 9 Production of X-rays hot cathode / filament labelled target indication of high voltage vacuum / shield / cooling / window Any two, X-ray inverse of photoelectric X-ray Electrons / cathode rays in radiation / light out Photoelectric electrons out radiation / light in 6 + Demonstrate photoelectric effect. suitable light // shine light metal plate / cap // photocell (negatively charged) electroscope // milliammeter leaves fall // current Einstein s explanation. photon / energy packet / quantum E = hf gives (all) energy to electron work function / threshold frequency or wavelength rest as kinetic energy of electron / electrons released (final x may be obtained by writing Einstein s photoelectric equation) Applications of photocell burglar alarm smoke alarms safety switch light meters automatic lights counters automatic doors control of central heating burners sound track in films scanner reading bar codes stopping conveyer belt + 11

12 Question 10 (a) Four fundamental forces gravitational electromagnetic strong (nuclear) weak (nuclear) Name of force for binding nucleus strong Two properties of force short range, strong(est), act on nucleons, binds nucleus Any two, x Outline of Cockroft and Walton moving protons high voltage alpha particles released screen / microscope Nuclear equation 1 1 H / 1 1 p He / α 1 H Li He He / He + Energy released E = mc Mass defect (kg) J 1

13 Question 10 (b) What is a semiconductor? resistivity between conductor and insulator Explain change in resistance increasing temperature frees more charge carriers/ electrons greater conductivity / lower resistance Sketch graph labelled axes concave upward curve Structure of transistor layers npn or pnp, labelled 1 connection to each layer Explain how circuit operates input voltage changes base voltage /current controls current through R / I c / voltage across R small change in input current / voltage large change in output current / voltage Sketch graphs of input and output voltages varying input magnified varying output out of phase Another use for transistor switch / inverter / current amplifier / logic gate / NOT gate 5 1

14 Question 11 (a) copper is a conductor. good F (b) force / Q per unit charge / explain symbols (c) experience (a large) force 7 (d) ions act as charge carriers 7 (moving / flowing ) (e) electrons / current / charge / flow(s) to or from ground through conductor / copper / air (f) neutralises charged clouds conducting charge /lightning / current to earth (g) act as (lightning) conductors 7 (current through body / injury / electrocution ) (h) point effect / point discharge (or implied) ( current) leakage / sparking / fire 1

15 Question 1 Marks awarded for the TWO best answered parts 1 (a) State principle of conservation of momentum momentum before = momentum after / equation no external force Mass of gas mv 50 m = m 1500 kg / 1515 kg Direction forward / towards space station / to right Change in direction gas expelled in one direction rocket in other direction 1 (b) Laws of refraction incident ray, refracted ray and normal in same plane Sin i/ Sin r is a constant Optical structure of eye shape of eye (labelled) lens labelled retina How does eye focus objects change shape of lens / accommodation changes focal length / focus / power Calculate (i) power (ii) focal length power = (-) 5 (m) (-) 0. m // (-) 0 cm 15

16 1 (c) em induction (induced) e.m.f (in a conductor / coil / wire) when magnetic flux / field changes Lenz s law direction of (induced) current / voltage / emf opposes change causing it Why is current reduced? (back) e.m.f. in coil increased magnetic flux // increases increases back e.m.f. // self inductance reduces voltage / reduces current Application dimmer switch / smooth d.c. / tuning radios / braking trains / damping in balances / induction coil 1 (d) Name the scientist Rutherford / Geiger / Marsden What was observed most alphas passed straight through 6 some deflected / scattered through large angles Why in vacuum to prevent alphas colliding with other particles (and being scattered) / range of alphas in air is (very) short 6 (any reference to collisions ) Conclusion nucleus / small dense core 6 positive / surrounded by empty space / orbiting electron cloud 16