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O Level Combined Science Practice Paper 1

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TuitionGoWhere Practice Paper - Combined Science O-Level

TuitionGoWhere Practice Paper (AI)
Version: 1 of 5
Subject: Combined Science (Physics Component Focus)
Level: O-Level (Sec 4/5)
Paper: Physical Sciences Practice Set
Duration: 1 hour 15 minutes
Total Marks: 65
Name: __________________________
Class: __________________________
Date: __________________________

Instructions to Candidates

Write your Name, Class, and Date in the spaces provided.
Answer all questions.
Write your answers in the spaces provided on the question paper.
An electronic calculator may be used.
You may lose marks if you do not show your working or if you do not use appropriate units.
Take the acceleration of free fall, $g = 10 \, \text{m/s}^2$ .
The total mark for this paper is 65.

Section A: Structured Questions

Answer all questions in this section.

1. A student measures the diameter of a metal wire using a micrometer screw gauge. (a) Define the term precision in the context of measurements. [1]

(b) The micrometer has a zero error of $+0.03 \, \text{mm}$. The reading on the scale is $2.45 \, \text{mm}$. Calculate the actual diameter of the wire.

Actual diameter = ____________________ mm
[2]

2. Fig. 2.1 shows the speed-time graph for a car moving along a straight road.

*(Imagine a graph: Speed increases linearly from 0 to 20 m/s in 5s, stays constant at 20 m/s for 10s, then decreases linearly to 0 in 5s.)*

(a) Describe the motion of the car during the first 5 seconds.
[1]

(b) Calculate the acceleration of the car during the first 5 seconds.

Acceleration = ____________________ $\text{m/s}^2$
[2]

(c) Calculate the total distance travelled by the car during the 20 seconds.

Distance = ____________________ m
[3]

3. A box of mass $15 \, \text{kg}$ is pushed across a horizontal floor with a constant horizontal force of $50 \, \text{N}$ . The box moves at a constant velocity. (a) State the magnitude of the frictional force acting on the box. Explain your answer.

Magnitude = ____________________ N
Explanation: _________________________________________________________________________
_____________________________________________________________________________________
[2]

(b) The pushing force is increased to $80 \, \text{N}$. The frictional force remains the same as in (a). Calculate the acceleration of the box.

Acceleration = ____________________ $\text{m/s}^2$
[3]

4. Fig. 4.1 shows a uniform metre rule pivoted at the $50 \, \text{cm}$ mark. A weight of $4.0 \, \text{N}$ is hung at the $20 \, \text{cm}$ mark. A weight $W$ is hung at the $80 \, \text{cm}$ mark to balance the rule horizontally.

(a) State the principle of moments.
[1]

(b) Calculate the value of weight $W$.

$W$ = ____________________ N
[3]

(c) The pivot is moved to the $40 \, \text{cm}$ mark. The $4.0 \, \text{N}$ weight is removed. Where must a $2.0 \, \text{N}$ weight be placed to balance the rule? (Assume the rule’s weight acts at the $50 \, \text{cm}$ mark and the rule has a weight of $1.0 \, \text{N}$).

Position = ____________________ cm mark
[3]

5. A hydraulic press is used to lift a car. The small piston has an area of $0.01 \, \text{m}^2$ and the large piston has an area of $0.5 \, \text{m}^2$ . A force of $200 \, \text{N}$ is applied to the small piston. (a) Calculate the pressure transmitted through the liquid.

Pressure = ____________________ Pa
[2]

(b) Calculate the force exerted by the large piston on the car.

Force = ____________________ N
[2]

(c) Explain why liquids are used in hydraulic systems instead of gases.
[1]

6. A crane lifts a load of mass $500 \, \text{kg}$ vertically through a height of $20 \, \text{m}$ in $10 \, \text{s}$ . (a) Calculate the work done by the crane against gravity.

Work done = ____________________ J
[2]

(b) Calculate the useful power output of the crane.

Power = ____________________ W
[2]

(c) The motor driving the crane has an input power of $15 \, \text{kW}$. Calculate the efficiency of the crane system.

Efficiency = ____________________ %
[2]

7. Fig. 7.1 shows a clinical thermometer and a laboratory thermometer. (a) State one structural difference between a clinical thermometer and a laboratory thermometer. [1]

(b) Explain why mercury is suitable for use in thermometers.
[1]

(c) A thermometer has a fixed point at $0^\circ\text{C}$ (ice point) and $100^\circ\text{C}$ (steam point). The length of the mercury thread is $2.0 \, \text{cm}$ at $0^\circ\text{C}$ and $22.0 \, \text{cm}$ at $100^\circ\text{C}$. Calculate the temperature when the length is $12.0 \, \text{cm}$.

Temperature = ____________________ $^\circ\text{C}$
[3]

8. A block of ice at $0^\circ\text{C}$ is heated until it becomes water at $20^\circ\text{C}$ . (a) Describe the energy changes occurring during the melting process in terms of kinetic and potential energy of the particles. [2]

(b) Explain, in terms of particle motion, why the temperature of the ice does not rise while it is melting.
[2]

9. Fig. 9.1 shows a vacuum flask used to keep hot drinks hot. (a) Explain how the silvered surfaces reduce heat loss. [1]

(b) Explain how the vacuum between the double walls reduces heat loss.
[2]

(c) Why is the stopper made of plastic or cork?
[1]

10. A wave travels along a rope. The frequency of the wave is $5 \, \text{Hz}$ and the wavelength is $0.8 \, \text{m}$ . (a) Calculate the speed of the wave.

Speed = ____________________ m/s
[2]

(b) State the difference between a transverse wave and a longitudinal wave.
[2]

(c) Give one example of a longitudinal wave.
[1]

Section B: Free-Response Questions

Answer all questions in this section.

11. A ray of light travels from air into a glass block. The angle of incidence is $40^\circ$ and the angle of refraction is $25^\circ$ . (a) Calculate the refractive index of the glass.

Refractive index = ____________________
[2]

(b) Calculate the critical angle for the glass-air boundary.

Critical angle = ____________________ $^\circ$
[2]

(c) Draw a ray diagram to show what happens to a ray of light inside the glass block when it hits the glass-air boundary at an angle of incidence of $50^\circ$. Label the incident ray, the reflected ray, and the angle of reflection.
[3]

(a) State one property that is common to all electromagnetic waves.
[1]

(b) Identify the region of the spectrum that:
    (i) causes sunburn.
    ____________________
    [1]
    (ii) is used for satellite communications.
    ____________________
    [1]

(c) Explain why ultraviolet radiation is more dangerous to human skin than visible light.
[2]

13. A plastic rod is rubbed with a cloth and becomes positively charged. (a) Explain how the rod becomes positively charged in terms of electron transfer. [2]

(b) The charged rod is brought near a small piece of neutral paper. The paper is attracted to the rod. Explain this observation.
[3]

14. Fig. 14.1 shows a circuit containing a battery, a switch, a fixed resistor $R$ , and a thermistor $T$ connected in series. A voltmeter is connected across the thermistor. (a) State what happens to the resistance of the thermistor as the temperature increases. [1]

(b) Explain what happens to the reading on the voltmeter as the temperature of the thermistor increases.
[3]

(c) Suggest one practical use for this circuit.
[1]

15. A student investigates the relationship between the current $I$ through a filament lamp and the potential difference $V$ across it. (a) Sketch the $I-V$ graph for a filament lamp. [2]

(b) Explain the shape of the graph in terms of the resistance of the filament.
[3]

16. Fig. 16.1 shows a simple d.c. motor. (a) State the function of the split-ring commutator. [1]

(b) State two ways to increase the speed of rotation of the motor.
1. _________________________________________________________________________
2. _________________________________________________________________________
[2]

(c) Explain why the coil rotates.
[3]

17. A transformer has 500 turns on the primary coil and 100 turns on the secondary coil. The primary coil is connected to a $240 \, \text{V}$ a.c. supply. (a) Calculate the voltage across the secondary coil.

Voltage = ____________________ V
[2]

(b) State whether this is a step-up or step-down transformer.
[1]

(c) Explain why a transformer does not work with a d.c. supply.
[2]

18. An isotope of Uranium, $^{238}_{92}\text{U}$ , undergoes alpha decay. (a) Write the nuclear equation for this decay, showing the symbol for the daughter nucleus. [2]

(b) State the nature of an alpha particle.
[1]

(c) Compare the ionizing power and penetrating power of alpha particles with gamma rays.
[2]

19. A Geiger-Muller tube is used to measure the background radiation in a laboratory. The count rate is 20 counts per minute. A radioactive source is placed near the tube, and the count rate rises to 220 counts per minute. (a) Calculate the count rate due to the source alone.

Count rate = ____________________ counts per minute
[1]

(b) The half-life of the source is 10 minutes. Calculate the count rate due to the source alone after 30 minutes.

Count rate = ____________________ counts per minute
[3]

20. A student wants to determine the density of an irregularly shaped stone. (a) Describe how the student can measure the volume of the stone using a measuring cylinder and water. [3]

(b) The mass of the stone is $50 \, \text{g}$ and the volume is $20 \, \text{cm}^3$. Calculate the density of the stone.

Density = ____________________ $\text{g/cm}^3$
[2]

(c) State the SI unit for density.
[1]

End of Paper

Answers

TuitionGoWhere Practice Paper - Combined Science O-Level (Answer Key)

Version: 1 of 5
Subject: Combined Science (Physics Component Focus)

Section A: Structured Questions

1. (a) Precision refers to the degree of exactness or the smallest division that can be measured by an instrument (or consistency of repeated measurements). [1] (b) Actual diameter = Reading - Zero Error $= 2.45 \, \text{mm} - 0.03 \, \text{mm}$ $= 2.42 \, \text{mm}$ [2]

2. (a) The car accelerates uniformly (constant acceleration). [1] (b) Acceleration $a = \frac{\Delta v}{\Delta t} = \frac{20 - 0}{5} = 4 \, \text{m/s}^2$ [2] (c) Distance = Area under graph. Area 1 (triangle) $= 0.5 \times 5 \times 20 = 50 \, \text{m}$ Area 2 (rectangle) $= 10 \times 20 = 200 \, \text{m}$ Area 3 (triangle) $= 0.5 \times 5 \times 20 = 50 \, \text{m}$ Total Distance $= 50 + 200 + 50 = 300 \, \text{m}$ [3]

3. (a) Magnitude = $50 \, \text{N}$ . [1] Explanation: Since the velocity is constant, the acceleration is zero. According to Newton's First Law, the resultant force is zero, so the pushing force equals the frictional force. [1] (b) Resultant Force $F_{net} = 80 \, \text{N} - 50 \, \text{N} = 30 \, \text{N}$ . $F = ma \Rightarrow 30 = 15 \times a$ $a = 2 \, \text{m/s}^2$ [3]

4. (a) For an object in equilibrium, the sum of clockwise moments about any pivot is equal to the sum of anticlockwise moments about the same pivot. [1] (b) Anticlockwise Moment $= 4.0 \, \text{N} \times (50 - 20) \, \text{cm} = 4.0 \times 30 = 120 \, \text{N cm}$ . Clockwise Moment $= W \times (80 - 50) \, \text{cm} = W \times 30$ . $120 = 30 W \Rightarrow W = 4.0 \, \text{N}$ . [3] (c) Pivot at $40 \, \text{cm}$ . Centre of gravity (weight $1.0 \, \text{N}$ ) is at $50 \, \text{cm}$ . Distance of CG from pivot $= 10 \, \text{cm}$ (Clockwise moment). Moment of rule weight $= 1.0 \times 10 = 10 \, \text{N cm}$ (Clockwise). Let $2.0 \, \text{N}$ weight be at distance $d$ from pivot on the left (Anticlockwise). $2.0 \times d = 10 \Rightarrow d = 5 \, \text{cm}$ . Position $= 40 - 5 = 35 \, \text{cm}$ mark. [3]

5. (a) Pressure $P = \frac{F}{A} = \frac{200}{0.01} = 20,000 \, \text{Pa}$ . [2] (b) Force on large piston $F = P \times A = 20,000 \times 0.5 = 10,000 \, \text{N}$ . [2] (c) Liquids are incompressible, whereas gases are compressible. This ensures efficient transmission of pressure. [1]

6. (a) Work Done $= mgh = 500 \times 10 \times 20 = 100,000 \, \text{J}$ . [2] (b) Power $= \frac{\text{Work}}{\text{Time}} = \frac{100,000}{10} = 10,000 \, \text{W}$ . [2] (c) Efficiency $= \frac{\text{Useful Power Output}}{\text{Input Power}} \times 100\%$ . Input Power $= 15 \, \text{kW} = 15,000 \, \text{W}$ . Efficiency $= \frac{10,000}{15,000} \times 100\% = 66.7\%$ . [2]

7. (a) Clinical thermometer has a constriction; laboratory thermometer does not. (Or: Clinical has a narrower range). [1] (b) Mercury is a good conductor of heat / expands uniformly / is opaque (visible) / does not wet glass. [1] (c) Range $= 22.0 - 2.0 = 20.0 \, \text{cm}$ for $100^\circ\text{C}$ . Change in length $= 12.0 - 2.0 = 10.0 \, \text{cm}$ . Temperature $= \frac{10.0}{20.0} \times 100 = 50^\circ\text{C}$ . [3]

8. (a) During melting, potential energy increases (bonds break/weaken) while kinetic energy remains constant. [2] (b) The heat energy supplied is used to overcome the forces of attraction between particles (increase potential energy) rather than increasing the kinetic energy of the particles. Since temperature is a measure of average kinetic energy, the temperature remains constant. [2]

9. (a) Silvered surfaces are good reflectors of infrared radiation (heat), reducing heat loss by radiation. [1] (b) A vacuum contains no particles. Conduction and convection require a medium (particles) to transfer heat, so heat loss by these methods is prevented. [2] (c) Plastic/cork are poor conductors of heat (insulators), reducing heat loss by conduction through the stopper. [1]

10. (a) Speed $v = f \lambda = 5 \times 0.8 = 4.0 \, \text{m/s}$ . [2] (b) In transverse waves, particle vibration is perpendicular to wave direction. In longitudinal waves, particle vibration is parallel to wave direction. [2] (c) Sound waves. [1]

Section B: Free-Response Questions

11. (a) $n = \frac{\sin i}{\sin r} = \frac{\sin 40^\circ}{\sin 25^\circ} = \frac{0.6428}{0.4226} \approx 1.52$ . [2] (b) $\sin c = \frac{1}{n} = \frac{1}{1.52}$ . $c = \sin^{-1}(0.6579) \approx 41.1^\circ$ . [2] (c) Diagram should show:

Incident ray hitting boundary.
No refracted ray emerging into air.
Reflected ray inside glass at angle of reflection $50^\circ$ .
Labelled "Total Internal Reflection". [3]

12. (a) They all travel at the speed of light in a vacuum ( $3 \times 10^8 \, \text{m/s}$ ) / They are all transverse waves / They can all travel through a vacuum. [1] (b) (i) Ultraviolet. [1] (ii) Microwaves. [1] (c) Ultraviolet has a higher frequency (and higher energy) than visible light. This higher energy can damage DNA in skin cells, leading to sunburn or skin cancer. [2]

13. (a) Electrons are transferred from the plastic rod to the cloth. The loss of negatively charged electrons leaves the rod with a net positive charge. [2] (b) The positive rod repels positive charges in the paper and attracts negative charges (electrons). This causes charge separation (polarization) in the paper. The negative charges are closer to the rod than the positive charges. The attractive force is stronger than the repulsive force, resulting in a net attraction. [3]

14. (a) Resistance decreases. [1] (b) As temperature increases, resistance of thermistor decreases. The total resistance of the circuit decreases. The current in the circuit increases. Since $V = IR$ for the fixed resistor, the voltage across the fixed resistor increases. Therefore, the voltage across the thermistor (which is Supply Voltage - $V_{resistor}$ ) decreases. [3] (c) Fire alarm / Temperature control system. [1]

15. (a) Graph starts at origin, curves with decreasing gradient (concave down). [2] (b) As current increases, the temperature of the filament increases. The increased temperature causes the metal ions to vibrate more vigorously, increasing the collision rate with electrons. This increases the resistance. Since $R = V/I$ , a higher resistance means a smaller increase in current for a given increase in voltage. [3]

16. (a) To reverse the direction of current in the coil every half rotation, ensuring the torque acts in the same direction for continuous rotation. [1] (b) 1. Increase the current. 2. Increase the strength of the magnetic field (or use stronger magnets). (Alternative: Increase number of turns on the coil). [2] (c) When current flows through the coil in a magnetic field, a force acts on each side of the coil (Motor Effect). These forces are in opposite directions (Fleming's Left Hand Rule) and create a turning effect (torque) that rotates the coil. [3]

17. (a) $\frac{V_s}{V_p} = \frac{N_s}{N_p}$ . $V_s = 240 \times \frac{100}{500} = 240 \times 0.2 = 48 \, \text{V}$ . [2] (b) Step-down transformer. [1] (c) A d.c. supply produces a constant current and thus a constant magnetic field. A constant magnetic field does not cut the secondary coil (no change in magnetic flux), so no e.m.f. is induced in the secondary coil. [2]

18. (a) $^{238}_{92}\text{U} \rightarrow ^{234}_{90}\text{Th} + ^4_2\text{He}$ (or $\alpha$ ). [2] (b) A helium nucleus (2 protons and 2 neutrons). [1] (c) Alpha particles have high ionizing power but low penetrating power (stopped by paper). Gamma rays have low ionizing power but high penetrating power (requires thick lead/concrete). [2]

19. (a) Count rate from source $= 220 - 20 = 200$ counts per minute. [1] (b) Time elapsed $= 30$ minutes. Number of half-lives $= \frac{30}{10} = 3$ . Initial count rate from source $= 200$ . After 1 half-life: $100$ . After 2 half-lives: $50$ . After 3 half-lives: $25$ counts per minute. [3]

20. (a) 1. Pour some water into the measuring cylinder and record the initial volume $V_1$ . 2. Tie the stone with a thread and lower it gently into the water until fully submerged. 3. Record the new volume $V_2$ . 4. Volume of stone $= V_2 - V_1$ . [3] (b) Density $\rho = \frac{m}{V} = \frac{50}{20} = 2.5 \, \text{g/cm}^3$ . [2] (c) $\text{kg/m}^3$ . [1]