phy2 2003

6732 Unit Test PHY2

1. Resistance of lamps

V2/R OR I = 60/12 = (5 A) 1

R=(12 V x 12 V) /60 W 1

R =2.4ohm 1 total 3

Resistance variation

Lamp A: resistance of A decreases with current increase 1

Lamp B: resistance of B increases with current increase 1

Dim filament

Lamps are dim because p.d. across each bulb is less than 12 V 1

Why filament of lamp A is brighter

Bulbs have the same current 1

p.d. across A > p.d. across B/resistance A> Resistance B 1

OR

power in A > power in B 2

total 8

2 Table

Physical Quantity - Typical value

Resistance of a voltmeter -10 M ohm

Internal resistance of a car battery - 0.05 ohm

Internal resistance of an EHT supply -10 M ohm

Resistivity of an insulator - 2.0 x 10¹⁵ ohm m

Drift velocity of electrons in a metallic conductor - 0.3 mm s^-1

Temperature of a working filament bulb - 3000 K

[Mark is lost if 2 or more values are put into one box] total 6

3. Current in heating element

P= VI 1

I = 500 W / 230 V 1

I = 2.2 A 1

Or

P=V²/R 1

R= 230 x 230/105.8 1

I = 2.2A 1

Drift velocity

Drift velocity greater in the thinner wire 1

Explanation

Quality of written communication. 1

See I = nAQv 1

is the same (at all points) 1

(probably) n (and Q) is the same in both wires 1 total 8

4 Resistance of films

R= pl/A 1

R = pl/wt or A = wt 1

Resistance calculation

R = (6.0 x 10^-5) (8 x 10^-3 m) / (3 x 10^-3m) (0.001 x 10^-3 m) 1+1

(Correct substitution but values in mm 1)

R= 160 ohm 1 ecf if in mm

Resistance of square film

L=w 1

R= pl/lt=p/t 1

R= pw/wt=p/t 1

Total 7

5. Definition of specific heat capacity

energy (needed) 1

(per) unit mass/kg and per unit temperature change K or C 1

OR

Correct formula [does not need to be rearranged] 1

with correctly defined symbols 1

Circuit diagrams (see end)

Accept voltmeter across heater and ammeter as well as voltmeter across heater only

Means of varying p.d./current 1

Voltmeter in parallel with a resistor symbol 1

Ammeter in series with any representionof a heater. 1

Other apparatus

(Top pan) balance / scales 1

Stopwatch / timer / clock 1

Explanation

Energy/heat loss to surroundings/air/bench 1

OR

Mc delta T +delta,Q = VIt or equivalent in words (e.g. student ignores energy loss in calculations) 1

Modifications

Any two from

Use of insulation around block

Ensure all of heater is within block

Grease heater/thermometer

Total 10

Specific Heat Capacity Calculation

C = delta Q/ m delta T = (860 x 10³)/ (1.4 kg) (750 – 22) = 844 (J kg ^–1 K^-1)

Conversion of kJ to J 1

Subtraction of temp 1

Answer 1

Energy transfers diagram

Label 2 (energy to) (warm) water (and trough) 1

Label 3 (energy used to) evaporate water / cause evaporation/latent heat/change of state 1

Total 5

Gas equation

PV = nRT [Accept symbols or words] 1

Molar gas constant unit

R= PV/nT

P – kgm^-1 s 1

V – m³ T– K n – mol all three for 1

Kinetic energy of molecule

Nm =M

density = Nm²>/3V correctly combined the 2 equations 1

Nm²> = 3nRT density = any mass –: volume 1

Show that

Kinetic energy =m²>/2=(3/2)n(RT/N) 1

Sketch graph

PV on y axis Temperature/’C on x axis

[accept axes reversed and correct graph] 1

Straight line graph with negative intercept 1

Gradient R 1

Intercept at – 273 ’C 1

[All these marks can be scored on graph)

total 10

8. Definition of e.m.f. of a cell

work/energy (conversion) per unit charge 1

for the whole circuit / refer to total energy 1

OR

Work/energy per unit charge 1

converted from chemical to electrical (energy) 1

OR

E = W/Q for whole circuit 1

All symbols defined 1

OR

E = P/I for whole circuit 1

All symbols defined 1

[Terminal p.d, when no current drawn scores 1 mark only] 2 max

Circuit diagram

See top

R 1

A in series 1

R (can be variable) 1 A and V correct 1 V as shown

Or across R+ A

Or across battery

[2nd mark is consequent on R(fixed, variable )or lamp]

Sketch graph

See top

Graph correctly drawn with axes appropriately labelled and consistent with the circuit drawn 1

Intercept on R axes equivalent to( – )r and Gradient equivalent to ( – )r [Gradient mark consequent on graph mark] 1

[Gradient may be indicated on graph]

Grade boundaries

A 41 B 37 C 33 D 26 E 25

phy1 2003

6731 Unit Test PHY1

1. Magnitude of resultant force

4 cm line S / 1.7 cm line N 1

8 cm line NE / 8N resolved into two perp. components (5.7E & 1.7N or 5.7N) 1

Correct construction for vector sum 1

5.7 – 6.1 N 1

Name of physical quantities

Vectors 1

Two other examples

Any two named vectors other than force (if >2, must all be vectors) 1

2. Calculation of average velocity

Use of v = s/t 1

v = 1.86 m s -1 / 1.9 m s -1 1

Acceleration of trolley

Selecting u = u + 2as 1

Correct substitutions 1

2.87 m s /2.9 m s /3.0 m s-1 1

Tension in string

Use of F = ma 1

2.73 N / 2.76 N / 2.85 N 1

Assuming no action other horizontal force/table smooth/light string/inextensible string 1

Explanation

Suspended mass/system is accelerating 1

Idea of resultant force on the 0.4 kg mass 1

4. Addition to diagram

Downwards arrow Y through middle third of left leg 1

Downward arrow Z with correct line of action 1

[Ignore lengths of arrows and point of action] [Must have at least one correct label to get 2 marks; no labels gets max 1 out of 2] [One correct label can get 2 marks]

Explanation

Quality of written communication

Clockwise moments = Anticlockwise when balanced

Y is smaller than X but acts further from P

Moment of XP /Moment of Y = F x YP

Z has little or no moment about P/Z acts through P

Gravitational potential energy

Use of mgh 1

Vertical drop per second = (8.4 m) sin (3) 1

-.9 x 10 J/Js -1/W 1

What happens to this lost gpe

Becomes internal energy/used to do work against friction and or heat energy. 1[mention of K.E. loses the mark]

Estimate of rate at which cyclist does work

Rate of working = 2 x 3.9 x 10 W 1

=7.8 to 10 W 1

[3.9 x 10 W earns 1 out of 2]

6. Momentum and its unit

Momentum = mass x velocity 1

Kgms-1 or N s 1

Momentum of thorium nucleus before the decay

Zero 1

Speed of alpha particle/radium nucleus and directions of travel

Alpha particle because its mass is smaller/lighter 1

So higher speed for the same (magnitude of) momentum OR Newton 3rd Law argument 1

Opposite directions/along a line 1

Nuclear equation

Correct symbol and numbers for tin OR beta 1

Correct symbols and numbers for the other two 1

Decay constant

Use of lambda = 0.69/ half life 1~

1.57 x 10^-15 y-1 OR 4.99 x 10 s-1 1

Activity of source and comparison with normal background count

rate

Use of A = lambda N 1

0.11/0.12 (Bq) 1

Lower (than background) [Allow ecf – assume background = 0.3 to 0.5] 1

8. Radiation tests

Alpha:

Test 2 or 2 and 1 1

Count drops when alphas have been stopped by the air / alphas have a definite range / (only) alpha have a short range (in air) 1

Beta:

Test 3/3 and 1, because 1 mm aluminium stops (some) beta/does not stop any gamma rays 1

Gamma:

Test 4 or 4 and 1, because 5 mm aluminium will stop all the betas, (so there must be gamma too)/gamma can penetrate 5 mm of aluminium

Table

Target for Alpha scattering

Gold atoms/gold foil gold leaf/gold film/very thin sheets of gold/metal foil etc. [NOT thin gold sheet] 1

Target for Deep inelastic scattering Protons/neutrons/nucleons /liquid hydrogen/nuclei 1

Conclusions

(i) Atom mainly empty space/nucleus is very small 1

Nucleus dense/massive 1

(ii) Nucleons have a substructure 1

Made of quarks 1

Phy2 2002

June 2002 PHY1

1.

C 1

A 1

B 1

E 1

2. Composition of alpha article

2 protons + 2 neutrons only 1

Explanation of ionize

Change nunber/Add/Remove electrons 1

Estimation of time alpha article would take to travel

Use of E = ½ mv2 1

Use of t = diameter/u 1

6.3 x 10^-18 s [ no ecf] 1

Explanation comparing speed of alpha and beta articles

Faster 1

Less massive/lighter/less weight (not smaller) 1

3. Explanation of essential difference between 2 definitions

Distance in direction of force against distance perpendicular to force 1

Correctly identifying which is which 1

Principle of moments

AP =80

,PB=32

[allow+ 1 ] [no ue ] 1

Demonstrate that moments are = equal. [allow any distance values] 1

Distance load at B raised

Use of work = force x distance / use of rngh [ beware m = 20 ] 1

Use of work out = work in / use of mgh lost = mgh gained 1

2.4x10 m 1

OR

Similar triangles/distance moved proportional to distance from pivot 1

x/6 x 10^-3 = 32/80 or equivalent 1

2.4x 10 m 1

4. Deceleration of cars

Acceleration = gradient / suitable eqn. of motion. 1

Correct substitutions [ 0.9 for t is wrong] 1

6.1 – 6.3 m s2[-ve value – 1] [ no ecf ] 1

Area under velocity -time graph

Distance/displacement 1

Shaded area

6.9 – 7.5 1

m 1

[Allow 1 mark for 5.5 – 6.1 cm .]

Minimum value of the initial separation

Both sloping lines continued down to time axis [by eye] 1

Explanation

Area between graphs is larger/B travels faster for longer/B still moving when A stops 1

Extra distance B goes is larger/ > 7.2 1

Initial separation must be larger 1

5. Experiment

2 light gates 1

Gate gives time trolley takes to pass [ not just ’the time’] 1

Speed = length of ’interrupter’/time taken 1

Or

2 ticker timers 1

dots at known intervals 1

speed = lenghth of tape / time taken 1

(ruler and clock method 1 mark max)

Total momentum of trolleys

Zero 1

It was zero initially or momentum is conserved [consequent] 1

Speed v of A

Use of momentum = mass x velocity 1

Use of mass x speed (A) = mass x speed (B) 1

1.8 m s -1 [ignore – ve signs] 1

6. Explanation of why kicking a door is more effective

Quality of written communication 1

Foot decelerates/ loses momentum 1

This takes place rapidly giving a large force by Newton 2 or equation versions [consequent] 1

Door is providing this force [consequent on mark 1] 1

Door acts on foot; by ’Newton 3’ foot acts on door 1 Max 3

7. Free-body force diagram

Normal reaction/contact force [or Nor R or push of table] upwards 1

E-M magnetic force [or magnetic attraction or pull of magnet] to right 1

Weight [or W or mg or gravitational force or gravitational attraction or pull of Earth] downwards 1

[Ignore labeled forces of action or drag] [if unlabeled – 1 each force]

Forces

Pull on earth 1

Upwards [consequent] 1

Or

Push contact / force on table 1

Downwards 1 [consequent]

Or

Force on magnet X 1

To left [consequent] 1

Precautions

Measure background radiation //shield apparatus 1

Subtract it off/ because it may vary//to eliminate background 1

Repeat the count and average 1

Because count (or emission) is random/varying 1

Source the same distance from GM on both occasions 1

Because count rate varies with distance 1 Max 3

[NB Marks must come from any TWO precautions.]

Ratio

0.88 or l. 1 [min. 2 sf] [not%] 1

Count for year 3

11 994 1

Graph

Suitable axes and scales [don’t award if factors 3, 7 used][not Bq] 1

Correct plotting of points 1

Use of curve and halving count rate 1

5.3 to 5.4 yr 1

9. Name of nuclei

Isotopes (not radioisotopes) 1

Nuclear equation

Electron numbers complete anywhere 1

Correctly balanced 1

Densest material

Sn 115 1