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120 Essential Concepts in Science (Physics)!
1.
Scalar Quantities are quantities that have magnitude only.
2.
Vector quantities are quantities that have both magnitude and direction.
3.
To add up 2 vectors that acts outwards from the same point,
the parallelogram law can be used.
4.
To add up 2 vectors that are continuous in direction, the
triangle law can be used.
5.
Speed is the rate of change of distance.
6.
Velocity is the rate of change of displacement / distance in a
distance / m
particular direction.
7.
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Acceleration is the rate of change of velocity.
8.
speed/ m/s
The gradient of a distance-time graph
gives the speed.
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150
100
50
20
40
60
80
100
120
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9.
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travelled while its gradient gives the acceleration.
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10.
The area under a speed-time graph gives the distance
20
30
40
50
60
time / s
When an object is dropped near the earth, its acceleration is constant at 10 m/s2 if
there is no air resistance.
11.
When the forces acting on a body are unbalanced, it will experience a resultant force and
it will accelerate because F = ma.
1
time / s
12. When the forces acting on a body are balanced, the resultant force acting on it is zero
and the body will either stay at rest / remain stationary or move with constant
velocity.
13.
Friction causes surfaces to heat up and results in wear and tear. It also reduces
efficiency in machinery.
14.
Mass is the amount of matter in a body.
15.
Weight is the gravitational force acting on the body.
16.
Mass is constant whereas weight depends on the gravitational field strength of the
location.
17.
Weight is measured in Newton (unit) using a spring balance.
18.
Mass is measured in kilogram (unit) using a beam balance.
19.
Mass is a scalar whereas weight is a vector.
20.
Inertia is the reluctance of a body to change its state of rest or motion.
21.
Density is the mass per unit volume.
22.
Gravitational field is a region in which a body experiences gravitational force.
23.
Gravitational field
strength is the
gravitational force
acting on a unit mass.
24.
Moment is the turning effect of a force.
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25.
Principle of moment states that when an object is in equilibrium, the sum of its
clockwise moment about any point is equal to the sum of its anticlockwise
moment about the same point.
26.
29.
A stable object has wide base area and low centre of gravity.
27.
Pressure is the force acting on a unit area.
28.
A force acting on a small contact area gives rise to a large pressure.
Conservation of energy states that energy cannot be created or destroyed but it can be
converted / transferred from one form to another.
30.
To increase the gravitational potential energy of a body, we need to increase its height
above the ground.
31.
To increase the kinetic energy of a body, we need to increase its speed.
32.
When a moving object is stopped by friction, its kinetic energy is converted to thermal
energy.
33.
When an object falls from a height, it gained kinetic energy while losing gravitational
potential energy.
34.
Power is the rate of work done.
35.
Solids have
fixed volume and shape and
it cannot be compressed.
36.
Liquids have fixed volume but its shape is not fixed. It is not easy / difficult to
compress and it assumes the shape of its container.
37.
Gases’ volume and shape are not fixed and it is highly compressible.
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38.
Solid particles are closely /tightly packed in a
regular / orderly pattern. They vibrate in their
fixed position. They have strong intermolecular
bonds between one another.
39.
Liquid particles are arranged randomly / freely
and they are close to one another. They vibrate and
move among one another. Their intermolecular forces are strong.
40.
Gas particles are spaced far apart and they move randomly with a fast / high speed.
Their intermolecular forces are negligible / very weak.
41.
When solid particles are heated, they will vibrate more vigorously , when liquid or
gas particles are heated, they will move faster.
42.
Thermal energy is transferred from a region of high
temperature to a region of low temperature.
43.
When a solid is heated, the particles gain energy and vibrate
more vigorously. They collide with their less energetic neighbours and transfer energy
to them. This transfer of energy from one particle to another by vibration is called
conduction.
44.
Metals are good conductors of heat while liquid / wood / plastic / wool / Styrofoam
and still (trapped) air are very good insulators of heat.
45.
When a fluid (liquid or gas) is heated, it will expand and become less
dense The hot fluid will rise to the top. The cooler fluid at the top
will sink to take its place because it is denser This circulation of fluid
is known as convection current and it will ensure that the fluid is
evenly heated.
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46.
Conduction and convection cannot occur in vacuum.
47.
Radiation is the transfer of heat by infrared wave.
48.
Radiation does not require a medium and is able to travel through vacuum.
49.
A good absorber of heat is a good emitter of heat.
50.
Rate of radiation depends on the texture , colour , area and
temperature of the surface.
51.
Black and rough surfaces are good in emitting / absorbing heat while
white and shiny surfaces are poor in emitting / absorbing heat.
52.
When an object
is heated, its temperature
increases because its kinetic / internal energy increases.
53.
Melting is the process in which solid changes into liquid at the melting point.
Solidification is the process in which liquid changes into solid at the freezing point.
54.
The heating curve shows how temperature varies
when a substance is heated. At VW, it is in the solid
state. At WX, solid and liquid states are in
equilibrium as the substance undergoes the
melting process. At YZ, it undergoes boiling
process whereby liquid changes into gas . Energy is
absorbed from V to Z but temperature does not change during the change of state
because it is used to break intermolecular bonds.
55.
Evaporation and boiling are similar because both involve
changing a liquid into a gas.
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56.
Boiling takes place at a fixed temperature whereas evaporation takes place at any
temperature below boiling point.
57.
A wave transfers energy by vibration. No matter is transferred when a wave moves.
58.
Transverse waves are waves that travel in a direction
that is perpendicular to the direction of vibration of
the particles in the medium.
59.
Longitudinal waves are waves that travel parallel
to the direction of vibration of the particles in the
medium.
60.
An example of longitudinal wave is sound wave while water wave is an example of
transverse wave.
61.
Amplitude of a wave is the maximum
dispalcement of the particles in the medium.
62.
Frequency is the number of complete wave
generated in 1s.
63.
Period of a wave is the time taken to generate a complete wave.
64.
Wavelength is the distance between 2 particles that are in phase / 2 crests / 2
troughs.
65.
Speed of the wave is the distance traveled by the wave in 1 s.
66.
Wavefront is an imaginary line that joins all the particles that are in phase in a wave.
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67.
Sound is produced by the vibration of objects.
68.
When an object vibrates, it alternates between pushing the air layers together to cause a
region of compression and pulling the air layers apart to cause a region of rarefaction
The air layers continues to vibrate parallel to the direction of the sound wave to
propagate the sound wave.
69.
Sound cannot travel in vacuum.
70.
Sound travel fastest in solid and slowest in gas.
71.
When sound is reflected echo is formed.
72.
A sound wave with a large amplitude is louder than a sound with a smaller amplitude.
73.
The higher the frequency of the sound wave, the higher the pitch of the sound.
74.
When light ray gets reflected, its angle of incidence is equal to
its angle of reflection.
75.
When light enters a different medium, it bends / gets
refracted because its speed changes.
76.
Light will bend towards the normal when it enters a denser
medium and bend away from the normal when it enters a less
dense medium.
77.
Refractive index of a medium is the ratio of the speed of light in vacuum and in the
medium.
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78.
Critical angle is the angle of incidence in the
denser medium when the angle of refraction
is 90o.
79.
When the angle of incidence in the denser
medium is less than critical angle, light will be
refracted out of the medium.
80.
When the angle of incidence in the denser medium is more than the critical angle, total
internal reflection will occur.
81.
Focal length of a lens is the distance between its optical
centre and principal focus.
82.
In order to use a converging lens as a magnifying
glass, the object must be placed at a distance less
than the focal length. The image obtained will be
virtual because it cannot be captured on a screen.
83.
When an object is placed at a distance equal to
the focal length of the lens, no image is formed
as parallel light rays emerged from the lens.
84.
A real and inverted image will be obtained when the
object is placed further than the focal length from
the lens.
85.
To obtain a real, inverted image that is of the same size as the object, it needs to be
placed at a distance equal to the 2 times the focal length from the lens.
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86.
Every wave in the electromagnetic spectrum is transverse in nature and they travel
with the same speed of 3 x 108 m/s in vacuum.
87.
Gamma wave has the largest frequency and the smallest wavelength in the
electromagnetic spectrum.
88.
There are 2 kinds of charges, positive charges and negative charges. Charges are
measured in Coulombs (unit).
89.
Unlike charges attract and like charges repel.
90.
Electric
Field lines of a positive and negative charge.
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91.
Electric field lines between (i) 2 like and (ii) 2 unlike charges.
(i)
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(ii)
92.
Current is the rate of
flow of charges. It is
measured with an ammeter that is connected in series to the circuit.
93.
Electrons flow in the opposite direction as the conventional current.
94.
Electromotive force (EMF) is the work done by an electrical source to drive 1 C of
charge around the complete circuit.
95.
The potential difference across a component is the energy needed to drive 1 C of charge
through the component. It is measured with a voltmeter connected in parallel across
the component.
96.
Resistance is defined as the ratio of potential difference and current.
97.
When the length of a wire is doubled, its resistance is doubled. When the crosssectional area of a wire is doubled its resistance is halved
98.
In a series circuit,

the current at every point is the same

the sum of the potential difference is equal to the EMF of the source

the effective resistance is the sum of the resistance in the circuit.
RE = R1 + R2
99.
In a parallel circuit,

the sum of the current that enters a point is equal to the sum of the current that
leaves the same point,

the potential difference across the separate branches is the same

the effective resistance can be obtained by the formula
1 + 1
RE = R1
R2
-1
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100. Fuses are used to prevent excessive current / current larger than its rating from
entering the circuit.
101. Earth wire prevents electric shock to the user when he accidentally touches
the metal casing of an appliance that has become live accidentally.
102. When the metal casing of an appliance becomes live accidentally, current will start to
flow to the earth through the earth wire. Since the resistance of the earth wire is small,
the current will be very large. That will blow the fuse and isolate the faulty appliance.
103. The fuse and switch must be connected to the live wire so that the appliance will be
isolated from high potential when the fuse blow or when the switch is closed.
104. The earth wire is yellow and green in colour, the neutral wire is blue in colour and the
live wire is brown in colour.
105. The neutral wire and earth wire are at zero potential (0 V) while the live wire is at
potential that is much higher or lower than the neutral wire to provide a potential
difference for current to flow.
106. If the casing of an appliance is made of an insulator, it is said to be double insulated.
107. Like poles of a magnet repel while unlike poles attract.
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108. A freely suspended magnet will always point in the north-south
direction.
109. Induced magnetism is the magnetism produced in a soft iron when a
magnet is brought near it.
110. To magnetise a magnetic material, it is put in a solenoid and a
direct current is passed through the solenoid. To determine the
polarity of the magnet, the right hand grip rule is used.
111. To demagnetize a magnet, it is put in a solenoid and an
alternating current (ac) is passed through the solenoid
and the magnet is pulled out of the solenoid slowly as the
current is still flowing.
112. The magnetic field of a bar magnet
113. The magnetic field between (i) 2 like poles (ii) 2 unlike poles of magnets
(i)
(ii)
114. Iron is easily magnetised and demagnetized. Hence it is used as an electro / temporary
magnet.
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115. Steel is difficult to magnetise and demagnetize. Hence it is used as a permanent
magnet.
116. The compass needle is made of permanent magnet while the electric bell is an example
of the application of temporary / electro magnet.
117. When current flows through a conductor, it produces a magnetic field.
118. Magnetic field of current flowing into (i) and out of the (ii) page
119. A current-
carrying conductor
experiences a
force when placed in a
magnetic field. The direction of the force can be determined by the Fleming’s left hand
rule.
120. When the direction of the current or magnetic field are reversed , the force acting on
the conductor will also be reversed.
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Congratulations! You have covered 120 essential Physics concepts!
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