stpm phys_p1 skema 2011

CONFIDENTIAL*

JAWATANKUASA PANEL TRIAL EXAM PHYSICS STPM

NEGERI SEMBILAN DARUL KHUSUS

MARKING SCHEME FOR

JPHYSli<CS STIP'M 1[JRJ[A]f I EXAM 2(()) Jl Jl

NEGJERJ[ SEI\.ffiJTIL.,AN

JPAPJER Jl(96(()/Jl)

(CONJFIDJENTJIAL)

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I. Which one ofthe following unit is derived unit?

A Candela B Mole C Second

-------------------------------------, I I 1 Answer: D '

. . Ulork Potential difference = -,-"--

charge

Energy

charge

E = V=-

Q I 1

'-------------------------------------~

v 2. A liquid flowing horizontally through a pipe abides by the relation

v where is the rate of volume flow of the liquid

t K is a dimensionless constant

pis difference in the liquid pressures at the two ends of the pipe

L is the length of the pipe

R is the radius of the pipe

What is the dimension of cp ?

ANSWER:B

t

D Volt

KpR4

rpL -,

, [kpR'] (ML'T-2 )(L' )(T)

['Jl]~ VL ~ (L')(L) ~ ML-1T 1

3. The diagram below shows the path of a ball that was projected at an angle of 45° to the horizontal.

By ignoring the resistance of the air, the magnitude of change in momentum from the initial point 0

to the final point P is

u

0 p

A .fimu mu

D mu

2mu c 2

B

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Solution: A

The horizontal change of momentum = 0

The vertical change of momentum

= mu sin45°- (-mu sin45°)

I I =mu-- (-mu-)

J2 J2

I =2mu-

J2

2

4. The maximum engine's power of the lorry of mass 2000 kg is 259 kW, the minimum time

required by the lorry to accelerate from rest to the speed of 45 ms- 1?

5.

A 40.0 s B 25.5 s c. 8.1 s

ANSWER:D

Use principle of conservation of energy

K.E gained = Energy supplied by the engine

V, mv2 = E = Pt

mv 2

t= ---2P

(2000)(45~) = 7_8s 2(259x!O')

A

v

D 7.8 s

An object of mass m moves with constant speed in a horizontal circle which has radius, r as shown in

the above diagram. Determine the value of work done and the change in momentum of the object

when it moves from point A to B?


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Work done Change in momentum

A Zero mv

B 22mv'

zero 21

c zero mv2

D zero zero

ANSWER:A

Work done = 0 ; F always perpendicular to direction of V

Change in momentum = mfl V ~-------

= m )v' + v2 ·- 2(v)(v)Cos60°

= mv

6. An external torque whose magnitude and direction are fixed acts on a rigid body hence causing

the body to rotate about a fixed axis, which one ofthe statements below is correct?

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A The magnitude of the external force which produces the torque increases.

B The angular velocity of the body does not change when the body is exerted by the

torque.

C The angular acceleration does not change when the body is acted on by the

torque.

D The rotational kinetic energy does not change when the body is acted on by the

torque.

ANSWER:C

Use r=la

Since I is constant then T is directly proportional to a

*This question paper is CONFIDENTIAL until the examination is over. CONFIDENTIAL'

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7

30.0 Kg

20.0 kg

The above figure shows a system in equilibrium with the 30 kg block just about to slide along a

horizontal surface. What is the coefficient of static friction between the 30 Kg block and the

horizontal surface?

A 020 B 050

T Sin 4..9::~ F, = ~R=~m, g ~ (1)

T Cos 46° = m2 g ~(2)

(1 );;f2) : Tan 46° =

Therefore m, tan 46°

~ = -

= 20tan 46' = 0.69 30

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c 0.69

*This question paper is CONFIDENTIAL until the examination is over.

D 0.87

R

30.0 Kg T T

20.0 kg

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8

The diagram shows the position of two identical satellites at radius ofR1 and R2 around the Earth. IfU,

K and E represent the potential energy, the kinetic energy and the total energy of the satellites

respectively. Which one of the following statements states correctly the comparison of the three

energies for satellite P and S

A UP< U,, Kv> K,

B UP< Us, K,<K,

c UP> Us, Kv<K,

D Up> Us, K, < K,

ANSWER: c

K = GMm ~ K a. llr 2r

~ E a -llr

and

and

and

and

E, <E,

E, <E,

Ep> Es

E, <E,

U=- GMm~ r

U a -1/r E=-GMm 2r

9 A particle is moving such that the force F on it changes with the distance r from a fixed point as

shown. F

r

Which graph best shows the relationship between the potential energy E, of the particle and the

distance r?


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A 8 c D

r r 0~ r

Answer: A

The particle is moving in SHM. F = - :~. where U is the potential energy. For potential energy

against distance graph, the gradient is overall positive followed by overall negative after t ~ 0

10 When damping is increased on an object undergoing resonant frequency oscillation, which change

does not occur?

A The amplitude of the driving oscillation decreases.

B The amplitude of the forced oscillation decreases.

C The resonant frequency decreases.

D The sharpness of the resonant peak decreases.

Answer: A

Answer A does not occur because the frequency of the driving oscillation is determined by the

oscillator and not by the driven system.

11 The diagram shows a long rope fixed at one end. The other end is moved up and down, setting up

a stationary wave.

vibration -·········-•.•

ugo~d •.••• / / ••• ··-t ... ..:.l··· ..---···'"····· .•.. fixed

• end

What is the phase difference between the oscillations at X andY?

I I A 0 B -;rrad C -Jrrad

4 2

Answer: A

D 3 -;r rad 4

Particles of rope within 2 nodes are of same phase. Hence phase difference is zero.

12 A sound wave is emitted from a point source. The intensity of the sound wave is inversely

proportional to the square of the distance from the source. At a distance r from the source, the

am2plitude of the wave is 8X. What is the amplitude at a distance 2r from the source?

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A 8X B 4X C 2X D X

Answer: B

fa-1

faA' 2 , r

2 1 1 A a-

2 orAa~then

r r k

A = ·~therefore r

Ar=k

A2r2 = A1r 1

A, =A,r, = (sxXrL4x r, 2r

13 A student blows across the top of a hollow bamboo pipe. The bottom of the pipe is closed

by a finger so that a fundamental tone of frequency f is produced. Then the student blows again with

the bottom of the pipe open. The tone that the student hears has a frequency

A equal tof B lower than/ C higher than/ D fluctuating in the range off

Answer: C.

In a closed pipe, the fundamental frequency f0 = c/4L where c is the speed of sound and L is the

length of the pipe. However, for the open pipe, the fundamental frequency, f0"c/ 2L.

So, f o = 2fo

14 The potential energy of a two-atom system is represented by

of U represents

U a b h .. = -2

- ~. T e m1mmum value r r

A the potential energy of the system when the atomic separation is a minimum.

B the potential energy of the system when the atomic separation is a maximum.

C the potential energy of the system when the resultant force between the atoms is zero.

D the gravitational potential energy of the system when the atoms are at their lowest position.

Ans:A F = - dU =the gradient of the U-r graph dr

15 Which of the following is the stress-strain graph for a glass rod which is stretched until broken?

S!r~ss • Stress Stress•, Stress l ' __ //

/ /' •'

I l

/ / I i

/ I /l I i 0 () I 0 0 /

Strain Strain Slrai~ S!fain

A B c D

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Answer: A Glass is brittle. It obeys Hooke's Jaw and in its stress-strain graph there is no plastic

region. It breaks when the elastic limit is exceeded.

16. At what temperature is the r.m.s. speed of oxygen molecules the same as that of helium

molecules at 300 K?

[Relative molecular mass of oxygen~ 32, relative molecular mass of helium= 4]

A 38K B 849K C 1440 K D 2400 K

D: c1

= · 3RTi = c2 = "8RT2 . M1 ' ~

17 The pressure p of an id•eal gas is related to the mean square

speed <c2 > ofthe gas molecules by the equation 71 = ~: T2 = ~2(300) K = 2400 K

I p =-nm < c2 >

3 What are represented by n and m?

n m

A Number of moles Mass of one mole gas

B Number of moles Mass of one molecule

c Number of molecules Mass of one molecule

D Number of molecules per unit volume Mass of one molecule

Answer: D

nm represents the density of the gas which is mass/volume

Mass of gas= number of molecules x mass per molecule.

mass/volume~ number of molecules per unit volume x mass per molecule.

18 An ideal gas undergoes isothennal change. If its initial internal energy is U1 and its final internal

energy is U2o the change in the internal energy is

A 0 D

Ans:A

19. The ratio of principal molar heat capacities for air is 1.4. When air of volume 500 cm3 at a

temperature of27"C is compressed adiabatically to a volume of 100 cm3, its new temperature is

A 187 "C B 298 "C C 326 "C D 385 "C

Ans: B

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T v:(r-1) =TV (r-1) 1 I 2 2

300x500(14- 1) = T2x!00(14- 1)

T = 300x( 500 )o.4 2 100

T, = 57!.1K

T, =298.l"C

20 One side of a room consists of a brick wall and a glass window. Both the brick wall and the glass

window have the same surface area. The thickness of the brick wall is 30 times that of the glass

1 . window, and the thermal conductivity of the brick is -that of the glass. The ratiO of rate of heat flow

6 through the brick wall to that of the glass window is

A 5: I B 180: 1 c 1 ; 5 D I :180

Ans:D

(Q) 1 (B1 -B,J Forbrickwall:- =-k.A ----(1) t b 6 30xg

For glass: (7)g =kg{~ :ge, J----(2)

(1) ( 7l 1 1 1 -·--=-x-=--(2) . ( 7) g 6 30 180

21 In an experiment to measure the thermal couductivity of a good conductor, a long test sample is

used so that

A the heat loss can be neglected

B the steady state is easily achieved

C the heat flow is parallel throughout the sample

D the temperature difference between the two ends of the sample is sufficiently large

Answer: D

Temperature gradient is small. A longer length is required to produce a sufficiently large

temperature difference.

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A

The above figure shows three negative charges with charge -q or -2q are placed at the vertices A, B

and C of an equilateral triangle in free space. The length of each of the three sides is 2.0 m and S is

the idle point of the side BC. What is the electric field strength at pointS?

A q

along AS 6m:,

c _q_ along SA

6m:,

ANSWER:C

' / 2.0 m \ / 2.0 m

\_~~' // A

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B .l!L 3Ju:,

D .l!L 3;r&,

along AS

along SA

SA= )2'-1 2 =.J3

Resultant E = Es + (-Ec) + EA

but= Ea=Ec

(direction S towards A}

*This question paper is CONFIDENTIAL until the examination is over. CONFIDENTIAL*

q

6nc0

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23. The diagram below shows the electric field lines between two parallel metal plates, A and B.

X lOOF

------~---.----~------

----'----;;--.----1-----,-- 0 v

If XY = _!_ XZ, determine the work done in moving an electron from X toY? 2

A C -8.0x!0-18 J

Answer: C E _ V _ !OOV _ SOV ---------

d Scm 2.5cm ++++++++

Wxv= qVxv = q (Vv-Vx)

=(-1.6 X 10'19 )(50-100)

= +8.0x!0'18J

A

~ B t t t t t t t t

24. A certain capacitor consists of a pair of parallel metal plates separated by a distance d in the air.

The capacitor is charged then disconnected from the charging source and immersed in a liquid with

permittivity E. Which of the following statements regarding the capacitor is correct?

A Both the charge stored in the capacitor and its capacitance decreased.

B Both the charge stored in the capacitor and its capacitance increased.

C The capacitance of the capacitor increased but the potential difference across it decreased.

D The capacitance of the capacitor increased but the potential difference across it increased.

Ans :C

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For parallel plate capacitor

C - s,A 0 -

d and

Sincee>&0 , thusC>C0

Q=CV

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Since Q ~constant, increase inC will result in decrease in V.

25. The circuit diagram shows a lO kQ resistor and a 40 kQ resistor connected across a charged

capacitor C,

After switch S is closed, the potential difference V across the capacitor varies with time t The

graph of In V against tis given as shown below.

In V

2

0'------~20.,---~ l(s)

The capacitance of the capacitor is

A L25 X 10-5 F

Answer: C

B 2,00 X 10- 4 F

V ~ Voe-tiCR

lnV ~ lnV -t/CR

Gradient of graph= 26 =- c1 • 1 1 1 s -

1 ("R =10kQ + 40kQ = 40kQ-,

c L25 X 10-3 F

Capacitance, C= (10)(40

: 10

,) F = 1.25 x 10-3 F

D 2.50 X 10-3 F

26. When a potential difference V is applied across the ends of a copper wire which has diameter d

and length I, the drift velocity of the electron is v. What is the drift velocity if the same potential

difference is applied across a copper wire ofhalfthe diameter but twice the length?

A v

B v c v D 2v

4 2

Answer: B

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ri' R1 =8R, [J t-''l ..... ·~ . - Since R = ~-

27. The resistance of a piece of pure silicon decreases rapidly with increasing temperature because

A the drift velocity of the charge carriers increases.

B the number of charge cat riers increases

C the ratio of negative charge carriers to positive charge carriers increases

D the ratio of positive charge carriers to negative charge carriers increases

Answer: B a= p RA

e

so, (j 0:: when Tt, R .J., crt and a= R

=> a oc n ; when n t, hence, crt.

m

28. A battery of e.m.f. 2.0 V and negligible internal resistance is connected to four resistors as shown

in the diagram below.

1 J J 20 [l IOD

2.ov 1 p v ·---< Q

10~ 100

What is the potential differer;ce between the points P and Q?

A OV B 0.33 V c 0.67 v D 1.00 V

Answer: B

The 20 Q , 1 OQ resistors and the 10 Q, I 0 Q resistors form the same potential dividers.

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---

20! ~v '""~ 3

WVT p -G>---to 10 3:.v 10!1 3

Hence the potential difference across P and Q ~ {;- 1) V ~ ~ V = 0.33 v

29 A milliammeter with negligible resistance gives a full scale deflection for 1 rnA. To convert it to a

voltmeter having a full scale deflection of 5 V,

A Connect a 5Q resistor in series with the milliammeter

B Connect a 50 D resistor in parallel with the milliammeter

c Connect a 5 X 1 03 n resistor in series with the milliammeter

D Connect a 5 n resistor in series with the milliammeter and a 5 X 1 03 n resistor in parallel

with the milliammeter I mA

Answer: C R

---·· VAB ~ 5V

V = l(R + r) = / R + l(O) Negligible resistance

5V~lrnA xR

.-. R = 5 X 102!1

B

30 An electron and a proton both entering perpendicularly in the same magnetic field separately. If

the speed of the electron is 10 times the speed of the proton. The ratio of the magnetic force on the

electron to the force on the proton is

A 1:1 B 1:5 c 1 : 10 D 10: I

Answer: D F~qvB therefore F, = lOq,

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31 If the current through a long solenoid is doubled while the coil's length is also doubled, keeping

the total number of turns constant, the magnetic field at a point inside near the axis is

A four times larger

B two times larger

c unchanged

D half the original size

Answer: C

therefore B 1 = B

32 When the speed of an electrical motor is increased due to a decreasing load, the current flowing

through it decreases. Which of the following is the best explanation ofthis phenomenon?

A The induced back e.m.f. increases

B The resistance of the coil changes

C Frictional forces inereased as the speed increases

D At high speeds it is more difficult to feed current into the motor

Answer: A

Back emf in de motor, Eb = NBArosin mt ; As the load decreasing, ro will increase. Then eb will

increase, due to Eb oc w. Current flows in de motor is I= 5

- cb , hence Eb increase, I will increase. R

33 A circular flat coil of 200 turns of wire encloses an area of I 00 cm2• The coil is immersed in a

uniform perpendicular magnetic field Of0.50 T that penetrate the entire area. If the field drops to zero

in 200 ms, what is the current induced in the coil if it has a resistance of 25 0?

A 0.20A B O.SOA

Answer: A

¢M = BA = 0.5 x 0.0 I = 0.0050 Tm2

I - ;c - o ~o • - ::-- ,..._ F1 _,

C l.OA D S.OA

34 An alternating current I which flow,, through a I 0 0 resistor is given by 1 = 3 sin I OOr. If I is in

amperes and tin seconds~ the mean power generated in the resistor is

A lOW B 30W C 45W D IOOW

Answer: C Mean power= •.;, !02 R = Yo(3)' (10) = 45 W

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35 The graph below shows the variation of reactance and frequency of an alternating current flowing

through three electrical components X, Y and Z.

Reactance

X

y

~--z "-----------+ Frequency

What are the components X, Y and Z?

X y z A Capacitor Resistor Inductor

B Inductor Resistor Capacitor

c Inductor Capacitor Resistor

D Resistor Capacitor Inductor

Answer: B

X is an Inductor, XL c" wL

Y is a resistor. Resistance is independent of frequency.

Z . . I ts a capacitor. X = ---

' 27r[C

36 The diagram shows a circuit of an inverting amplifier.

An input voltage of +2 V produces an output voltage of ·-8 V. Which statement about the circuit is

not true?

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A

B

c D

Rl The value of -is 4.

R,

The voltage gain is- 4.

When the input voltage is -1 V, the output voltage is+ 4 V.

When the input voltage is 2 V, the potential at point P is 2 V. Answer: D V r = 0 V


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37 If the input voltages V1 and V2 in the circuit below are 50l!V and 90 l!Y respectively, what is

the output voltage? [Gain~ 105]

+ 15 v

~~~--------------~ov

Ans :B

v, 105

v, -~

~ l0 5 (40x!0-6)

~4.0 v

B 4.0 V C +15V D -15V

38 The propagation of an electromagnetic wave is accompanied by electric field oscillations and

magnetic field oscillations. Which of the following statements is not true concerning the

electromagnetic wave?

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A The electromagnetic wave can be polarized.

B The electric field oscillations and the magnetic field oscillations are in phase.

C The directions of the electric field oscillation, the magnetic field oscillations, and the

electromagnetic field are perpendicular to one arwther.

D The oscillating frequency of the electric field and the oscillating frequency of the

magnetic field change when electromagnetic wave propagates from one medium to another

medium. Answer: D (factual)


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39 The diagram below sbows a long glass rod with uniform diameter 2r. The left end of the rod

has a semicircular convex surface of radius r. The refractive index of the glass is n. An object 0 is

placed on the left side and at the axis of the rod.

I I I I I I I I I

!~ ~~-----!"'- u ----71 v ' '

I I I I >I

If the image distance v produced in the rod is twice the object distance from the end of the rod, the

object distance u is

(n+2)r A 2n

Answer: B

~+~=~ u 't' ;•

1 '1'1 11-1 -+-=-t~ 2u r

B (n+2)r

2 (n-1: c 2(n-1)r

(n+2)

n+2 n-1

2u r

'· U= (11 + Z)r 2(n- 1)

D 2(1-n)r

(n +2)

40 A monochromatic light is directed towards a single adjustable slit to produce a diffraction

pattern on a screen as shown.

Intensity Central maximum

Subsidiary maxima

0

When the width of the slit is reduced,

A the intensity of the central peak will increase and the intensity of the subsidiary maxima will

decrease.

B the intensity of all maxima will increase and the width of the pattern will decrease.

C the intensity of all maxima do not change and the width of the pattern will increase.

D the intensity of all maxima will decrease and the width of the pattern will increase.

Answer : D The intensity will decrease when the width of the slit is reduced because there

is less light entering the slit. The width of the pattern will increase because the diffraction effect is

better when the width of the slit is narrower.

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41 The diagram below shows a light beam incident on the surface of glass which has been coated

with an optical material.

f

If the wavelength of light in the optical material is A and the reflective index for the optical material

and the glass are n 1 and n2 respectively, which ofthe following is the condition for the reflected light

beams x andy to experience destructive interference?

A ;\

t =- and n1 > n2 • B

c )! t =- and n1 < n2 2

D t = i\ and n, < n,

Answer: B

A light beam experiences a phase change of n when reflected at the air-glass interface where

the reflective index n1 of glass is greater than the reflective index n2 of air. Hence, the path

difference between light beams x andy ;

= Zt +-2

=2m+~=3m

This will produce destructive interference.

42 Which of the following is true based on the photoelectric effect?

A The emission of electrons will not occur for very low light intensity.

B The number of electrons produced per second does not depend on the intensity of light.

C The maximum velocity of the electrons increases when the wavelength of light decreases.

D The average kinetic energy of the electrons decreases when the frequency of light increases

Answer: C

K = .:::S_ 1.v max }.

A decreases, Kmax or Vmax increases


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43 If electron A has twice the kinetic energy of electron B, the ratio of the de Broglie wavelength of

electron A to that of electron B is

A I: 2 B

Answer: B £.4 = 2ER v/ =2vl VA= \~VB

c 2: 1 D

44 A hydrogen atom absorbs a photon and "' a result an electron is excited from the ground state to

the second excited state. If the n,h energy level of the hydrogen atom is given by E, =-13

·6 eV the 2 ,

n photon energy absorbed is

A 3.4 eV B 10.2 eV C 13.6 eV D 12.1 eV

ANSWER:D

Energy of photon absorbed= Energy excited from energy level n=l to energy level n=3

13.6 13.6 v =E3 -E1 =(-~eV)-( -~e ) = 12.1 eV

32 12

45 The property ofthe metal should be chosen as a target anode in an X-ray tube is

A a good conductor of electricity

B a good conductor of thermal energy

C a good insulator of thermal energy

D a good reflector of thermal energy

Answer: B

46 The mirror fixed at the end of the tube in a helium-neon laser system is used to

A improve the rate of production of electrons

B increase stimulated emission of photons

C absorbed part of the photons

D reduces the loss of laser light from the system

Answer: B

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47 The mass of the nucleus ;;cu, the mass of nucleus :Hand the mass of ; n are 62.9296 u,

1.00783 u, and 1.00867 u respectively. What is the binding energy per nucleon for the nucleus?

A 5.40 X 10-13 J B D 8.85x 10-11 J

ANSWER: C

E = l\mC 2 = (29x 1.00783 + 34x 1.00867- 62.9296) (1.66x 10-27 )(3 x 108 )= 8.85 x J0- 11 J

Binding energy per nucleon= 8.85 x 1 o-11

63 =1.40x 10-12 J

48 A radioactive isotope of an element X experiences a series of decays until it becomes a stable

isotope for element X. In the process, the ratio of number of a particles emitted against the number of

~ particles emitted is

A 2:2 B 2: I c I : 2 D I : 1

Answer: C

Working: , u A-•x 2 a z.lle---t z + -Ie

49 Helium nucleus is produced when a lithium nucleus is bombarded by a proton, as shown in the

below equation:

If the speed of light is c, mass of lithium is me. mass of proton is mp and mass of helium is mH , which

of the following expressions represents the energy released in this nuclear reaction?

A (me+ mp+2 mH) c2

B (me+mp-2mH)c2

C (me+ 2 mH - mp) c2

D (me+ 2 mH + mp) c2

Answer: B

50 Which one of the following is the main characteristic of a quark?

A It has zero rest mass

B It travels at the speed of light

C It has fractional charge

D It is a combination of baryons

Answer: C


stpm phys_p1 skema 2011

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