o General physics
• The density of an object only changes when the
substance is heated or cooled.
• An object sinks if its density is more than the liquid on
which it is placed on, but floats if less dense.
• When there is no air resistance the acceleration of any
object is constant (constant= 10m/s)
• Easier to lift an object on the moon because gravity is
less on the moon.
• Resultant Force.
• Gravitational, electrostatic and magnetic forces can be
applied from a distance, other than that you have to be in
contact with the object to apply a force.
• A force applied on an object can cause a change in
speed, direction and shape.
• Acceleration, velocity etc. is a vector quantity.
• When an object moves in a circle it is accelerating and
at constant speed at the same time; because the direction
is changing but the speed is constant.
• Centripetal force is caused by tension in the string (ball
on a string), gravity (satellite in space), friction between
the tires and the road (a car on the road).
• For an object to be in equilibrium state the resultant
force has to be equal or zero (forces up = forces down) and
the resultant moment has to equal zero (clockwise moment
= anticlockwise moment).
• For the stability of an object it has to have a wide base
and a low center of mass.
• To find the center of mass draw two points A and B,
hang the object from each hole so that it can swing freely.
Tie a weight to each point then draw the vertical line, the
center of gravity is where the lines intersect.
• When a car is going up a hill K.E. = Same, G.P.E =
Increases, Chemical Energy (petrol) = Decreases and the
total energy stays the same as energy is not lost, created
• Internal energy = Thermal energy.
• Fission = Process called when large molecules break
down into small. Example: power station of uranium.
• Fusion = Process called when small molecules builds
into large molecule. The fusion process produces more
energy than fission. Example: Sun.
• The mass lost is converted into heat energy.
• In barometers the space at the top is a vacuum,
because air would prevent the mercury from rising.
• The width of the barometer does not affect the height of
• Water manometers are more accurate to measure gas
• To get the total pressure, remember to add the
• The gas pressure can be converted from mm of Hg to Pa
by using P = density*gravity*height, but remember to use
the total pressure.
• Pressure= force/area
• The more the area, the more the force & the less the
area the, the less the force.
• The pressure is the same on all the walls of the
containers as the molecules move in a random motion.
• Temperature is proportional to K.E. + Molecules hit the
walls harder and more often.
• Brownian motion: The tiny, fast-moving air molecules,
which are in a constant random motion, are hitting the
larger smoke particles from all directions.
• Evaporation: It is the vaporization of liquid, when the
fast moving molecules/energetic molecule leave the surface
without the temperature reaching its boiling point.
• The greater the surface area, the more the evaporation
• Evaporation occurs at surface of liquid: no bubbles.
• Boiling occurs throughout the liquid: bubbles appear.
• We feel cold after bath because the high energetic
molecule evaporate leaving behind, dull/less energetic
• Thermal expansion: molecules gain kinetic energy and
force results in pushing each other further apart.
• Volume = less area so the particles hit the walls harder
and more often.
• Mercury is used to measure high temperature.
• Alcohol is used to measure low temperatures.
• The capillary tube of a thermometer is narrow so a
small change in temperature results in a large change in
volume of the liquid.
• Thermocouples have a low specific heat capacity this
means they can measure rapidly changing temperatures
and they don’t take much heat away from the object they
are measuring the temperature of them.
• During melting or boiling the temperature stops rising
because extra energy is needed, which is taken from the
heat source, to overcome the strong forces of attraction
which are holding the molecules together. This energy will
not increase the speed of the molecules it will only break
• In an experiment the value for the latent heat of fusion
is too low as energy is taken in from the surroundings
which melt the ice.
• In an experiment the latent heat of vaporization is too
high as energy is lost to the air from the heater therefore
not all the energy is used for evaporating the water.
• The value for the latent heat of vaporization is much
higher than the value for fusion because a large amount of
energy is needed to break the bonds between the
molecules to move them far apart
• Energy= Mass x Specific heat capacity x Change in
• Energy to break bonds= Mass x Latent heat of
o Waves, Light & Sound
• Waves transfer energy from one place to another.
• There are 2 types of waves: Transverse and
• Transverse wave: A wave in which the particles vibrate
perpendicular, to the direction of movement. A complete
wave consists of 1 crust and 1 trough. E.g. Light waves
• Longitudinal wave: A wave in which the particles vibrate
back and forth in the direction of movement. It consists of
compressions and rarefactions. E.g. Sound waves
• Compressions are the area in a wave where the
particles are closer to each other and the pressure in that
area is highest.
• Rarefactions are the area in a wave in which the
particles are far apart and the pressure is least.
• The larger the frequency and amplitude the greater the
energy of the wave.
• When a wave gets refracted, its Speed decreases,
Wavelength decreases, Frequency = Same.
• When a wave gets reflected, it’s Speed = Same,
Wavelength = Same, Frequency = Same.
• When a wave gets diffracted, it’s Speed = Same,
Wavelength = Same, Frequency = Same.
• Radio waves are easily diffracted because they have a
• In the spectrum of light all the colors have the same
speed, but different wavelengths & frequencies.
• Objects that produce light are called luminous objects
and the object which uses the light from source to reflect
and make it see is called illuminated objects.
• When a light wave travels from a less dense material to
a more dense material, the refractive index is more than 1.
• When a light wave travels from a more dense material
to a less dense material, the refractive index is less than 1.
• A fish in a pond appears to be higher than it actually is
because light refracts.
• Total incidence angle is always = Total reflection.
• Refractive index = speed of light in air/speed of light in
• Remember that when the ray is passing from less dense
to more dense the formula applied is Refractive index = sin
i/ sin r
• But when it passes from more dense to less dense we
use Refractive index = sin r/ sin i.
• Reflective index = 1/sin C (C stands for critical angle).
• Total internal reflection is when the ray is travelling to a
less dense material from a more dense material and also if
the incidence angle is above 42 degrees.
• The center of a lens is called its optical center, C.
• The line through C at right angles to the lens is called
the principle axis.
• The fatter the lens, the stronger it is and the shorter its
• Parallel light, e.g. Sun, must be used to find the focal
length of a lens.
• When the object is beyond 2F the image comes in
between F and 2F, real, inverted and smaller than the
• When the object is in between F and 2F the image
comes beyond 2F, real, inverted and same size as the
• When the object is before F the image appears in, real,
inverted and smaller than the object.
• Dispersion of white light occurs because each fraction of
white light has a different wavelength, so they are slowed
down by different amounts.
• A spring is used to represent longitudinal waves.
The speed of sound in:
Air 330 m/s
Water 1400 m/s
Wood 4000 m/s
• Ripple tank can be used to see transverse wave.
• When a loudspeaker moves out the air is compressed,
when it moves in the air is rarefied.
• Frequency = number of vibrations per second.
• Speed (m/s) = Frequency (Hz) x Wavelength (m)
• The speed of sound increases as the particles move
• Gamma Rays, X-Rays, Ultra-Violet are Carcinogenic.
1.Gamma Rays Sterilize food & equipment, Treat Cancer
2.X-Rays Go through body to check for broken bones
3.Ultra-Violet Suntan, Make fluorescent materials glow
4.Light Allows you to see
5.Infrared Heating, Remote Control, Mobile phones,
6.Microwaves Send messages, Cook food
7.Radio & T.V. Send messages
o Electricity & Magnetism
• Ferrous (magnetic) metals are Iron, Steel, Nickel &
• The true test for a magnet is that it repels another
• When a ferrous metal is magnetized the domains are
turned so that they are lined up.
• Making Magnets: Stroking, Electrically (D.C.) &
• Demagnetizing a magnet: Heating, Hammering, and
• Uses of permanent magnets: Compasses, Door catches.
• Uses of electromagnets: Scrap yards, Electric bell, and
• Conductors have free moving electrons in them,
• In electrostatic experiments metals cannot be used as
they are good conductors of electricity and don’t stay
• In ammeters and voltmeters Red terminal = Positive,
Black terminal = Negative.
• Current in a series circuit always remains same but gets
divided in parallel.
• Voltage in a series gets divided but