7/27/2019 2010 S4 BT2 Answers

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Marking Scheme2010 BT2 Sec 4 Physics

Section A

Qn 1 2 3 4 5 6 7 8 9 10

Ans B D D A B B B C A D

Qn 11 12 13 14 15

Ans A C B A D

Section B

Qn Remarks

16ai The soft iron bar is a magnetic material.

Since magnetsalways attract magnetic materials,when R moves, S will follow.

[1m] for magnetic material orbecomes an induced magnet

[1m]

16aii As S is further from the magnet, the magnetic fieldstrength of the magnetbecomes weaker.

The force of attraction is not strong enough tohold onto S/ pull S along which will fall.

[1m] for mentioning magneticfield is weaker

[1m]

accept magnetic force isweaker than gravitationalforce

16b His decision is not good / unwise.

The iron facade will shield/block the magnetic field

of the magnet in R from reaching the soft iron in S.S will always fall off as there is no magnetic forceattracting it.

[1m]

[1m] for reasonable explanation

17a Soft iron [1m] accept iron

17b Soft iron can be easily magnetised and easilydemagnetised .

[1m] must incl. both magnetised

and demagnetised must incl. easily

17c The relay switch will not close.

This is because copper is not a magnetic material, Itwill not produce amagnetic field strong enough toattract the relay switch and close the high voltagecircuit.

[1m]

[1m] must indicate that the

magnetic field is not strongenough to attract orno magnetic field to attract

7/27/2019 2010 S4 BT2 Answers

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2010 Block Test 2 PhysicsSecondary Four

2 Nanyang Girls High School

Setters: KC, AJL, MH & TW Physics / BT2

18ai[1m] for correct arrow direction

18aii The coil will rotate in the opposite direction.

OR

The coil will rotate in an anti-clockwise direction.

[1m]

allow ecf depending onanswer in 18ai

18b P : carbon brushQ : split-ring commutator

[1m] for both correct answers

18c increase the current in the circuit,use battery with higher e.m.f.,use stronger magnets,increase the number of turns of the coil,use a wire with lower resistance

[2m] for any two correctanswers

19a When the coil rotates, there is a change in themagnetic field lines linked to the coil.

As a result, an e.m.f. is induced in the coil.

When the coil is connected to an external circuit,current will flow.

[1m]

[1m]

19b

[1m] for correct shape (cosine)

[1m] for correct timing

[1m] for correct amplitudes

if shape is wrong, allow ecffor time and amplitudes

must indicate at least t = 0.5 sand 1.0 s (time for half andfull oscillations)

must indicate 0, 4.0 V and -4.0 V on y-axis

s.f. is not considered

voltage / V

time / s0 0.50 1.00.750.25

4.0

-4.0

7/27/2019 2010 S4 BT2 Answers

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2010 Block Test 2 PhysicsSecondary Four

3 Nanyang Girls High School

Setters: KC, AJL, MH & TW Physics / BT2

20ai n = 1 / sin C= 1 / sin 46o= 1.39 (to 3 s.f.)

[1m][1m] allow 2 s.f. (ie. n = 1.4)

20aii r = 180o 30o 44o 90o= 16o

sin i = n x sin r= 1.39 x sin 16o= 0.3831

i = 22.5o (to 3 s.f.)

[1m]

[1m]

[1m] for correct answer

if n= 1.4 is used, acceptanswer in 2 s.f.

20b

20bi [1m] for drawing (i)

[1m] for drawing correct lensposition with label L

no mark if label L not shown accept no arrowhead do not accept ecf

20bii [1m] for drawing (ii)[1m] for correct position of focal

length with label F

no mark if label F not shown

allow ecf if lens position iswrong

accept no arrowhead

20biii [1m] for drawing (iii)

allow ecf if lens position iswrong

accept no arrowhead

(i)

L

F

(ii)

(iii)