O Level – Physics

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Turning Effect of Forces

1. The moment of a force about a pivot is the product of the force F and the perpendicular distance d from the pivot to the line of action of the force.
Moment of a force = F x d

2. The SI unit for moment of a force is newton metre (N m).

3. Moment of a force is a vector. The direction of the moment of a force is either clockwise or anticlockwise about the pivot.

4. There are two conditions for an object in equilibrium:
(a) Net external force F = 0
(b) Net moment due to external forces = 0 (also known as the Principle of Moments)

5. The Principle of Moments states that when an object is in equilibrium, the sum of the clockwise moments equals the sum of the anticlockwise moments.

6. The centre of gravity of an object is the point at which its entire weight appears to act. The
centre of gravity of regular-shaped objects can be determined by geometrical symmetry. The centre of gravity of irregular-shaped objects can be determined by the plumb line experiment.

7. The stability of an object increases when the base area increases or when the centre of gravity is lowered.

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Energy,Work and Power

1. Energy is the ability to do work.

2. Energy can exist in many forms. It can be converted from one form to another.

3. Gravitational potential energy Ep is the energy possessed by an object due to its position in a gravitational field.

Ep = mgh

4. Kinetic energy Ek is the energy possessed by an object due to its motion.

Ek = 1/2 m v^2

5. The Principle of Conservation of Energy states that the total amount of energy in an isolated system is constant.

Total initial energy = total final energy

6. Work done on an object W is the product of force F acting on the object and distance s travelled by the object in the direction of the force.

W = Fs

7. The SI unit of energy and work done is the joule (J).

8. Power P is the rate of work done W. Power can also be defined as the rate of energy conversion E.

P = E/t

9. The SI unit of power is the watt (W). It can also be expressed in joule per second (J s-‘).

10. Efficiency is the ratio between useful energy output Eoutput. and energy input Einput.

Efficiency = Eoutput/Einput

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Pressure

1. Pressure p is the force F acting on a surface divided by the area A of the surface.

P = F/A

2. The SI unit of pressure is pascal (Pa) or newton per square metre (N m-2).

3. Pressure p at a certain depth h of a liquid with density p under the influence of gravitational field strength g is given by the following relationship:

p = hpg

4. According to Pascal’s Principle, an extra pressure applied at any part of a body of liquid will be experienced throughout the liquid. In a hydraulic press, an extra pressure applied at one end will be experienced by the other end.

5. According to the Principle of Conservation of Energy, the work done at one end of a hydraulic press is equal to the work done at the other end.

Fx x dx= Fy x dy
(where F is the force applied on/by the piston d is the distance moved by the piston)

6. Atmospheric pressure is exerted due to the weight of the atmosphere. Its average value at sea level is 1.013 x 10^5 Pa.

7. The barometer is a simple device used to measure atmospheric pressure. The height of liquid level in the vacuum-filled tube increases if the atmospheric pressure increases

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Temperature

1. Temperature (T) is a measure of how hot or cold an object is. It is an indication of the amount of heat energy of an object.

2. The SI unit of temperature is the kelvin (K). However, the degree Celsius (°C) is more commonly used.

3. A thermometric property is a physical property that changes according to temperature. To define a temperature scale, a thermometric property that varies linearly with temperature is used.

4. In the Celsius scale, two fixed points are used: ice point and steam point. They are 0°C and 100°C respectively. Each interval on the thermometer measures 1°C.

5. A thermometer is a device used to measure the temperature of an object.

6. Using a thermometric property that varies linearly with temperature, the value of the unknown temperature T is determined by the following equation:

T = (XT – X0)/(X100 – X0)

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2014 Aug O level Physics Intensive Revision

29-Jul Tue 7pm to 9pm 2 hrs Sound & P1 Exam Practice

1-Aug Fri 4.30pm to 6pm 1.5 hrs Sound & P1 Exam Practice

3-Aug Sun 10.30pm to 12pm 1.5 hrs Kinematics and Dynamics & P1 Exam Practice

3-Aug Sun 1pm to 2.30pm 1.5 hrs Sound & P1 Exam Practice

5-Aug Tue 7pm to 9pm 2 hrs Light & P2 Exam Practice

8-Aug Fri 4.30pm to 6pm 1.5 hrs Light & P2 Exam Practice

10-Aug Sun 10.30pm to 12pm 1.5 hrs Forces and Moments & P2 Practice

10-Aug Sun 1pm to 2.30pm 1.5 hrs Light & P2 Exam Practice

12-Aug Tue 7pm to 9pm 2 hrs Electromagnetic Waves & Sound

15-Aug Fri 4.30pm to 6pm 1.5 hrs Electromagnetic Waves & Sound

17-Aug Sun 10.30pm to 12pm 1.5 hrs Energy, Work and Power & P1 Exam Practice

17-Aug Sun 1pm to 2.30pm 1.5 hrs Electromagnetic Waves & Sound

19-Aug Tue 7pm to 9pm 2 hrs Current Electricity & P2 Exam Practice

22-Aug Fri 4.30pm to 6pm 1.5 hrs Current Electricity & P2 Exam Practice

24-Aug Sun 10.30pm to 12pm 1.5 hrs Pressure & P2 Exam Practice

24-Aug Sun 1pm to 2.30pm 1.5 hrs Current Electricity & P2 Exam Practice

26-Aug Tue 7pm to 9pm 2 hrs D.C. Circuits & P1 Exam Practice

29-Aug Fri 4.30pm to 6pm 1.5 hrs D.C. Circuits & P1 Exam Practice

31-Aug Sun 10.30pm to 12pm 1.5 hrs Thermal Physics & P1 Exam Practice

31-Aug Sun 1pm to 2.30pm 1.5 hrs D.C. Circuits & P1 Exam Practice

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Chapter 1 Measurement

Exam Tip 1
It is important to use SI units. A physical quantity without the appropriate unit is ambiguous, e.g. 5 units of length can represent 5 cm, 5 m or 5 km.
Many students are not careful enough in writing symbols. Do not use Kg (capital letter K for kilogram and M for metre.)

Exam Tip 2
Common e.g. of SI units using prefixes: millimetre (mm), centimetre (cm), kilometre (km), etc. Candidates must remember all the prefixes, their symbols and meanings.

Exam Tip 3
When using graphical method to find the resultant force of two forces.
The length of the diagonal in the diagram is not the actual resultant in most cases. Students need to refer to the scale chosen to calculate the resultant.

Exam Tip 4
A student has been asked to calculate the volume of a piece of wire, which is about 80 cm long and about 0.2 cm in diameter.
Which measuring instruments should the student use?

To answer a question like this, candidates need to know the accuracy of different measuring instruments

Exam Tip 5
The INSIDE jaws of a pair of vernier calipers can be used to measure the internal diameter of measuring cylinder and beaker.

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2015 Schedule – Physics

S3 1.5 hrs SAT 10.30am – 12pm

S3 1.5 hrs SAT 2pm – 3.30pm

S3 1.5 hrs SUN 1pm – 2.30pm

S4 1.5 hrs FRI 4.30pm – 6pm

S4 1.5 hrs SAT 2pm – 3.30pm

S4 1.5 hrs SUN 10.30am – 12pm

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Chapter 2 Kinematics Part 1

Exam Tip 1
An example to show non-zero distance but zero displacement: An object is under a circular motion. It completes one revolution and goes back to the starting point. The distance travelled is the circumference of the circular path but the displacement is zero.

Exam Tip 2
An example of constant speed but changing velocity: When an object is under circular motion, the direction of motion changes with time. Its speed can be the same but the displacement keeps changing when the object is moving along the circle.

Exam Tip 3
A misconception for acceleration is that many students think that acceleration must be zero if an object is at rest. This is not always true.

A case of zero velocity but non-zero acceleration: When an object is thrown upwards, it is momentarily at rest at the highest point. The velocity is zero. However it is a free falling body as gravity is the only force acting on it.

For free falling body, the acceleration is always 10 m/s^2 (if there is no air resistance) no matter whether it is moving downwards, upwards or at rest momentarily

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Chapter 2 Kinematics Part 2

Exam Tip 4
Uniform acceleration means uniform increasing speed, i.e. the change of velocity (or speed) is a constant.

Exam Tip 5
Students should be able to describe the different kinds of motion of an object by reading distance-time or speed-time graph. They should be able to describe the change in distance, speed and acceleration

Exam Tip 6
Apply area formula for triangle, rectangle or trapezium according to the graph to find the distance travelled under the Velocity-Time graph

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Chapter 2 Kinematics Part 3

Exam Tip 7
An important point for a free falling body:
A free falling body may also move up-wards. When a free falling body is rising instead of falling, its direction of motion is upwards but the acceleration is -still 10 m 5 2 downwards.
This upward motion will slow down even-tually because the acceleration due to gravity is opposing its direction of motion.
In fact, this free falling body is deceler-ating. When its velocity becomes zero, it will stop at that position momentarily and then start falling again. The free falling body is now accelerating.

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Chapter 2 Kinematics Part 4

Exam Tip 8

EFFECT OF AIR RESISTANCE

When an object is in motion (either on the ground or in the air), there is always air resistance acting on the moving object in a direction OPPOSITE the direction of motion.

– Air resistance is a FRICTIONAL FORCE which:
– Increases with the surface area (size) of the object;
– Increases with the speed of the object;
– Increases with the density of air.

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Secondary 3 Year End Exams and Secondary 4 Prelim Preparatory Classes

for Physics.

Open for Registration Now!

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Measurement

Question 1

Which pair of units both measure the same quantity?
A km/h and kg/m3
C V and J/C
B N/m3 and Pa
D W and J

Ans C
Potential Difference V = Work done per unit charge = J/C

Question 2

Which instrument is used to measure directly the circumference of a golf
ball?
A calipers
B micrometer
C rule
D tape

Ans : D
A cloth tape can be used to directly measure the length along a curved surface, such as the circumference of a golf ball.

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Light – Reflection

1. The diagram below shows a ray of light being reflected from a plane surface

2. The following terms are commonly used in the reflection of light

Normal – Imaginary line perpendicular to the surface of reflection
Angle of incidence, i – Angle between the incident ray and the normal
Angle of reflection, r – Angle between the reflected ray and the normal

3. Laws of reflection:
(a) Angle i = Angle r
(b) The incident ray, reflected ray and the normal at the point of incidence all lie on the same plane.

4. Characteristics of an image formed in a plane mirror:
(a) Upright
(b) Virtual (Cannot be captured on a screen)
(c) Laterally inverted
(d) Same size as the object
(e) Image distance from the other side of the surface of reflection is the same as the object’s distance from the surface of reflection.

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