 |
 |
 |
 |
 |
 |
 |
 |
Light is a form of energy that travels away from the source producing it at a speed of
.Law 1: The incident ray, the normal ray at the point of incidence and the reflected ray all lie in the same plane.
Law 2: The angle of incidence is equal to the angle of reflection (i = r).
A virtual image is formed by the apparent intersection of rays.
Such an image can never be formed on a screen. It can be located by the method of no parallax
The apparent movement of one object relative to another due to the motion of the observer is called parallax.
The object that is farthest from the observer always appears to move with the observer.
A real image is an image formed by the actual intersection of light rays.
Such an image can be located on a screen or by the method of no parallax.
If the object is outside the focus the image is real and is located in front of the mirror.
If the object is inside or at the focus the image is virtual and is located behind the mirror.
Light from any point on a distant object arrives as a beam of parallel light.
The image is always virtual and located behind the mirror.
The image is always diminished. The nearer the object is to the mirror the bigger the image.
The bending of a ray of light when it goes from one medium to another is called refraction.
When light travels from a rarer to a denser medium it is refracted towards the normal.
When light travels from a denser to a rarer medium it is refracted away from the normal.
1st Law: The incident ray, the normal ray at the point of incidence and the refracted ray all lie in the same plane.
2nd Law: The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant.
i.e.
,
where n is a constant The refractive index of a medium is the ratio of the sine of the angle of incidence to the sine of the angle of refraction
when light travels from a vacuum into that medium.
The refractive index between two media is the ratio of the sine of the angle of incidence to the sine of the angle of refraction
when light travels from one of those media into the other.
When light travels from a denser to a rarer medium
the angle of incidence whose corresponding angle of refraction is 90°
is called the critical angle (C) for those two media.
When light going from a denser to a rarer medium
strikes the second medium with an angle of incidence greater than the critical angle,
it does not enter the second medium.
It is reflected back into the denser medium. This is called total internal reflection.
A very thin transparent rod (usually of glass) through which light can travel
by total internal reflection is called an optical fibre.
If the object is outside the focus the image is real and
located at the opposite side of the lens to the object.
The image is inverted.
If the object is inside the focus the image is virtual and
is located at the same side of the lens as the object.
The image is upright (erect).
Displacement is distance in a given direction.
Velocity is the rate of change of displacement with repect to time.
Acceleration is the rate of chage of velocity with respect to time.
A velocity-time graph of a body moving with constant acceleration is a straight line.
The slope is accelereation.
The area under the graph is the distance travelled.
In the absence of air resistance, all objects near the Earth's surface,
if released, will fall downwards with the same acceleration.
The acceleration is called acceleration due to gravity. Its symbol is g.
A quantity that has magnitude only and has no direction in space is called a scalar quantity.
A quantity that has both magnitude and a direction in space is called a vector quantity.
If two vectors, drawn tail to tail, are the adjacent sides ab and ad of the parallelogram abcd,
the diagonal from a to c of this parallelogram is their resultant.
If two vectors are drawn head to tail
the vector from the head of the first to the tail of the second is their resultant.
Anything that causes the velocity of an object to change is called a force.
The mass of a body is a measure of how difficult it is to accelerate that body.
The unit of mass is the kilogram.
The weight of an object is the force of the Earth's gravity acting on it.
Momentum is the mass of an object multiplied by it's velocity.
The unit of momentum is the kilogram metre per second (kg m s-1)
Newton's first law of motion: (MIX)
Every body will remain in a state of rest or travelling with a constant velocity
unless an unbalanced external force acts on it.
Newton's second law of motion: (MIX)
When an unbalanced force acts on a body the rate of change of the body's momentum
is directly proportional to the force and takes place in the direction of the force.
Newton's third law of motion: (MIX)
If a body A exerts a force on a body B,
then body B exerts an equal but opposite force on body A,
i.e. For every action there is an equal and opposite reaction.
In any interaction between two or more bodies
the total momentum of the bodies before the interaction
is equal to the total momentum after the interaction
provided no external force acts on the system of bodies.
The density of a substance is its mass per unit volume.
The unit of density is the kilogram per cubic metre (kg m-3).
Pressure is force per unit area.
The unit of pressure is the pascal (Pa).
One pascal is equal to one newton per square metre.
When an object is partially or completely immersed in a fluid
it experiences an upthrust equal in magnitude to the weight of the fluid displaced.
The law of flotation states that the weight of a floating body is equal to the weight of the fluid it displaces .
Boyle's law states that at constant temperature
the volume of a fixed mass of gas is inversely proportional to its pressure.
Any two point masses in the universe attract each other with a force
that is directly proportional to the product of their masses
and inversely proportional to the square of the distance between them.
The moment of a force about an axis is equal to the magnitude of the force
multiplied by the perpendicular distance from the axis to the line of action of the force.
The unit of moment is the newton metre (N m).
If a body is in equilibrium then
the vector sum of the forces in any direction is zero
the sum of the moments about any point is zero
When a force F moves through a displacement s in the direction of the force,
the work W done is equal to the force multiplied by the displacement.
Work =Force xdisplacement , W = Fs
One joule is the work done when a force of one newton
acts for a distance of one metre in the direction of the force.
1 J = 1 N m
Energy is the ability to do work. The unit of energy is the joule (J).
Energy cannot be created or destroyed but can only be converted from one form to another.
The kinetic energy (Ek) of a body is the energy it has due to its motion.
The potential energy (Ep)of a body is the energy it has due to its position in a force field.
A source of energy that does not get used up is called a renewable source of energy.
Power is the rate at which work is done.
or
Power is the rate at which energy is converted from one form to another.
The unit of power is the watt (W).
Angular velocity is the rate of change of angle with respect to time.
The unit of angular velocity is the radian per second (rad s-1)
If a body is moving in a circle the force towards the centre needed to keep it moving is called centripetal force.
If a body is moving in a circle the acceleration towards the centre of the circle is called centripetal acceleration.
The time taken for a satellite to go once around the central body
is called the periodic time or simply the period (T) of the orbit.
When an object is bent, stretched or compressed by a displacement s,
the restoring force F is directly proportional to the displacement,
provided the elastic limit is not exceeded.
A body is said to be moving with simple harmonic motion if:
(i) its acceleration is directly proportional to its distance from a fixed point of its path and
(ii) its acceleration is always directed towards that point.
Temperature is the measure of the hotness of a body. The SI unit of temperature is the kelvin (K).
Any physical property that changes measurably with temperature is called a thermometric property.
The heat capacity of an object is the heat energy needed to change its temperature by 1 K (1oC).
The specific heat capacity (c) of a substance is the heat energy needed
to change the temperature of one kilogram of that substance by one kelvin.
The unit of specific heat capacity is the joule per kilogram per kelvin (J kg-1 K-1)
The latent heat (L) of an object is the heat energy needed to change its state without a change in temperature
The specific latent heat (l) of a substance i
s the amount of heat energy needed to change the state of one kilogram of that substance
without a change in temperature.
The specific latent heat of fusion of a substance
is the amount of heat energy needed to change one kilogram of that substance
from a solid to a liquid without a change in temperature.
The specific latent heat of vaporisation of a substance
is the amount of heat energy needed to change one kilogram of that substance
from a liquid to a gas without a change in temperature (i.e. at its boiling point.)
The unit of specific latent heat of fusion and of vaporisation is the joule per kilogram (J kg-1)
Conduction is the movement of heat energy through a substance
by the passing on of molecular vibration from molecule to molecule.
There is no overall motion of the substance.
The U-value of a structure is the amount of heat energy conducted per second
through 1 m2 of that structure
when a temperature difference of one degree celcius is maintained between its ends.
Radiation is the transfer of heat energy from one place to another in the form of electromagnetic waves.
The average amount of the Sun's energy falling per second
perpendicularly on one metre squared of the Earth's atmosphere
is the solar constant.
Its value is about 1.35 kW m-2.
Convection is the transfer of heat through a fluid by means of circulating currents caused by the heat.
A travelling mechanical wave is a disturbance carrying energy through a medium without any overall motion of that medium.
A travelling wave, either mechanical or electromagnetic, is a disturbance that travels out from the source producing it, transferring energy from the soure to other places through which it passes.
A transverse wave is a wave where the direction of vibration is perpendicular to the direction in which the wave travels.
A longitudinal wave is a wave where the direction of vibration is parallel to the direction in which the wave travels.
The maximum distance of any particle from its undisturbed position is called the amplitude (A). Thus the distance from the crest (or trough) to the undisturbed position is the amplitude.
The distance from any point on one cycle to the corresponding point on the next cycle is called the wavelength (
)
of the wave. The distance from one crest to the next is the wavelength, as the distance is on trough to the next.
Wavelength is measured in metres.
The number of cycles passing any point per second is called frequency (f).
Frequency is measured in numbers of cycles per second. 1 cycle per second is called 1 hertz (Hz).
The bouncing of waves off of an obstacle in their path is called reflection of waves.
The changing of direction of a wave when it enters a region where its speed changes is called refraction.
The sideways spreading of waves into the region beyond a gap or around an obstacle is called diffraction.
When waves from two sources meet, a new wave is produced.
The displacement produced at any point by this wave is the algebraic sum of the displacements that each wave would produce on its own.
This is called interference of waves.
When waves from two sources meet and the amplitude of the resulting wave is greater than the amplitudes of each of the individual waves,
the waves are said to undergo constructive interference.
When waves from two sources meet and the amplitudes of the resulting waves is less than the amplitude of each of the individual waves,
the waves are undergoing destructive interference.
Two sources of periodic waves are said to be coherent if they are in phase
or if there is a constant phase difference between waves from each of the sources.
If this is so the sources must also have the same frequency
When waves from two or more coherent sources meet, the resulting wave pattern formed is called an interference pattern.
When two periodic travelling waves of the same frequency and amplitude moving in opposite direction meet,
they interfere with each other. The resulting wave formed is called a stationary wave or a standing wave.
The apparent change in the frequency of waves due to the motion of the source or the observer is called the Doppler Effect.
Frequencies which are multiples of a certain frequency are called overtones of that frequency.
If f is a given frequency 2f is its first overtone 3f is its second overtone etc.
The loudness of a sound wave depends on the amplitude of the sound wave.
The greater the amplitude the greater the loudness.
The pitch of a note depends on the frequency of the sound wave
The higher the frequency the higher the pitch, the lower the frequency the lower the pitch.
The quality of a note depends on the number of overtones present in the note
and the relative strengths of the different overtones present.
The frequency limit of audibility are the highest and lowest frequencies that can be heard by a normal human ear.
The range is 20 Hz - 20 000 Hz.
If the frequency of a periodic force applied to a body is the same as or very near to its natural frequency
that body will vibrate with very large amplitude. This phenomenon is called resonance.
The sound intensity (I) at a point is the rate at which sound energy is passing through unit area
at right angles to the direction in which the sound is travelling at that point i.e. I = P/A.
Sound intensity level is measured in decibels (dB)
The threshold of hearing is the smallest sound intensity detectable by the average human ear at a frequency of 1 kHz.
Its value is 1x10-12 W m-2.
A string vibrating with an antinode at its centre and a node at each end
(and no other nodes or antinodes) is vibrating at its fundamental frequency.
Frequencies which are multiples of a certain frequency f are called harmonics.
f is called the fundamental frequency or the first harmonic.
If f is the first harmonic, 2f is the second harmonic, 3f is the third harmonic etc.
Experimentally it is found that for a stretched string
-the greater the length l, the lower the fundamental frequency,
-the higher the tension T, the higher the fundamental frequency
-the greater the mass per unit length u, the lower the fundamental frequency.
In a pipe closed at one end only odd numbered harmonics may be present.
In an open pipe all harmonics may be present.
a Move the eyepiece relative to the cross-threads until the cross-threads are in focus.
b View a distant object with the telescope
and move the cross-threads and eyepiece together relative to the objective lens
so that the distant object appears in focus.
c Illuminate the slit. Move the slit relative to the collimator so that the slit is in focus.
d Adjust the width of the slit, if it is too wide or too narrow.
e Level the turntable by means of the levelling screws.
The distance d between two adjacent slits (i.e. the width of one line and one slit) on the grating is called the grating constant or the grating spacing.
The fact that light can be polarised shows that light is a transverse wave.
The separating out of the different wavelengths (colours) present is light is called dispersion.
Red, green and blue are the primary colours of light.
When two primary colours are mixed in equal intensity, the colour formed is a secondary colour.
Yellow, cyan and magenta are the secondary colours of light.
A primary colour and the secondary colour that when mixed give white are called complementary colours.
If an object is negative charged (-) it has gained electrons.
If an object is positively charged (+) it has lost electons.
It is only the electrons that actually move when an object becomes charged.
The unit of electric charge is the coulomb (C).
Any substance through which electric charge cannot flow is called an insulator.
Any substance through which electric charge can flow is called a conductor.
All static charge resides on the outside of a conductor.
Static charge tends to accumulate where the conductor is most pointed.
The force of attraction or repultion between two point chares is directly proportional to the product of the charges and inversly proportional to the square of the distance between them.
An electric field is any region of space where a static electric charge experiances a force other than the force of gravity. An electric field is always caused by other static charges in the vicinity.
An electic field line drawn in an electric field showing the direction of the force on a positive charge placed on the field.
The electric field strength in an electric field is the force per unit charge at that point, i.e. electric field strength is the force per coulomb.
The unit of electric field strength is the newton per coulomb which is the same as the volt per metre.
The potential difference (V) between two points in an electic field is the work done in bringing a charge of +1 coulomb from one point to the other.
The unit of potential difference is the joule per coulomb. This unit is also called the volt (V).
The potential difference between two points is 1 volt if 1 joule of work is done when one coulomb is brought from one point to the other.
An electric current is a flow of electric charge.
The potential difference between a point and the Earth is called the potential of that point.
The capacitance (C)of a conductor is the ratio of the charge on the conductor to its potential, i.e. C = Q/V.
The unit of capacitance is the farad (F).
A conductor has a capacitance of 1 farad if placing a charge of 1 C on it it raises its potential by one volt, i.e. 1 farad =1 coulomb per volt.
Electric current is a flow of charge.
A voltage when applied to a circuit is called an emf.
An ammeter measures current. It must be connected in series.
A galvanometer measures very small currents.
A voltmeter measures potential difference. It must be connected in parallel.
An ohmmeter measures resistance.
The resistance (R) of a conductor is the ratio of the p.d. acros it to the current flowing through it, i.e.
.A conductor has a resistance of 1 ohm if the current through it is 1 ampere when the p.d. across it is 1 volt.
The current through an ohmic conductor is directly proportional to the p.d. across its ends as long as the temperature remains constant.
For a conductor of length l,cross sectional area A and resistance R, the resistivity,
,(rho)
is given by
.Joule's law states that the rate at which heat is dissipated in a conductor i directly proportional to the square of the current as long as the resistance remains constant.
.An atom or molecule that has lost or gained one or more electrons is called an ion.
In an electrolyte the charge carriers are positive and negative ions.
The kilowatt-hour is the amount of energy used by a 1000W appliance in one hour.
A semiconductor is a substance whose resistivity is between that of a conductor and an insulator.
Its resistance decreases as temperature increases.
A thermistor is a device whose resistance decreases rapidly with increasing temperature.
A light dependent resistor (LDR) is a semiconductor device whose resistivity decreases when light is incident upon it.
When an electron breaks free from a covalent bond it leaves behind a (positive) hole.
Instrinsic conduction occurs in a pure semiconductor due to thermal agitation. The current contains equal numbers of holes and electrons.
The adding of a controlled amount of impurity element to a semiconductor is called doping.
If a group V impurity element is added to a pure semiconductor it becomes an n-type semiconductor.
The number of free electrons is greater than the number of holes, i.e. the majority charge carriers are free electrons.
If a group III impurity element is added to a pure semiconductor it becomes a p-type semiconductor.
The number of holes is greater than the number of free electrons, i.e. the majority charge carriers are holes.
The increased conduction in a doped semiconductor is called extrinsic conduction.
A p-n junction occurs where a p-type semiconductor is in contact with an n-type semiconductor.
The depletion layer is a narrow region spanning both sides of a p-n junction.
It contains no free majority charge carriers and behaves like an insulator.
When holes and free elctrons cancel each other in the depletion layer of a p-n junction a potential difference is formed across the junction. This is called the junction voltage.
A diode is connected in forward bias if the positive terminal of the battery is connected to the p-type side and the negative terminal is connected to the n-type side. A diode has a low resistance in forward bias.
A diode is in reverse bias if the positive terminal of the battery is connected to the n-type material and the negative terminal is connected to the p-type material. In reverse bias a diode has a high resistance as the depletion layer extends to cover the entire diode.
A magnetic field is a region of space in which a magnet will experience a force. The direction of a magnetic field is that in which a north pole would move.
A magnetic field line is a line along which a north pole would move.
If the right-hand clasps a conductor with the thumb pointing in the direction of the current, then the fingers give the direction of the magnetic field.
A curren, I, t in a magnetic field, B, experiences a force, F.
(FBI rule): On the left hand, if the first three digits are held at right angles to each other, the thumb points in the direction of the force, F, the index finger points in the direction of the magnetic field B, and the long finger points in the direction of the current, I.
The magnetic flux density at a point is equal to the force experienced by a conductor of length 1 metre carrying a current of 1 ampere when the conductor is at right angles to the field. It is a vector quantity. Its direction at a point is the direction in which a north pole would move.
The magnetic flux density at a point is 1 tesla (T) if a conductor of length 1 m carrying a current of 1 A experiences a force of 1 N when it is placed perpendicular to the field.
An ampere is that current which when flowing through two infinitely long parallel conductors of negligible cross section one metre apart in a vacuum would produce between them a force of 2x10-7Newtons per metre of length.
The coulomb is the amount of charge that passes any point in a circuit when a current of 1 ampere flows for 1 second.
Whenever the magnetic field passing through a coil changes, an emf appears in the coil. This phenomenon is called electromagnetic induction.
The magnetic flux,
,
threading a area A at right angles to a magnetic field of flux density
B is given by
. Its unit is the weber (Wb).If the magnetic flux density over an area of 1 square metre is 1 tesla then the flux through the area is 1 weber.
The size of the e.m.f., E, induced in a loop is directly proportional to the rate of change of flux,
.
.States that the direction of an induced current is always such as to oppose the change producing.
If a changing magnetyic field in one coil causes an induced emf to appear in a nearby coil there is said to be mutual induction between the two coils.
Whenever the current passing through a coil changes, the magnetic field surrounding that coil changes. This changing magnetic field induces an emf in the coil that opposes the chaning current (i.e. a back emf). This phenomenon is called self induction.
Back e.m.f. gives a coil (an inductor) a higher resistance to a.c. than to d.c.
A capacitor block d.c. but allows a.c. to pass.
The transformer consists of two coils wound on a common soft iron core.
A transformer steps an a.c. voltage up or down.
Thermionic emission is the giving off of electrons from the surface of a hot metal.
Streams of high speed electrons moving from the cathode are called cathode rays.
One electronvolt (eV) is the amount of energy gained or lost by a single electron when moving through a potential difference of one volt. (1 eV = 1.6x10-19 J.)
A beam of electrons moving a right angles to a magnetic field moves in a circle.
The photoelectric effect is the emission of electrons from the surface of a metal by electromagnetic radiation of a suitable frequency.
In a photocell the photocurrent is directly proportional to the intensity of the light.
For a given metal the frequency below which photoemission will not occur is called the threshold frequency.
The work function,
,
of a metal is the minimum energy needed to remove the loosest electron from
the surface of that metal.A photon is a packet of electromagnet energy. It has particle properties.
X-rays are high frequency electromagnet radiation produced when high speed electrons in a cathode ray tube strike a metal target with a high melting point.
When light from a luminous sourcve undergoes dispersion the resulting pattern is called an emission spectrum.
An energy level is a fixed energy value that an electron can have in an atom.
The atomic number (Z) of an element is the number of protons in the nucleus of an atom of that element.
The total number of protons and neutrons in the nucleus of an atom is called the mass number (A) of that atom.
Isotopes are atoms of an element that have the same number of protons but different numbers of neutrons.
Radioactivity is the spontaneous disintegration of nuclei with the emission of one or more types of radiation.
Alpha particles (
)are
helium nuclei.Beta particles (
)
are high speed electrons.Gamma radiation (
) consists of high-frequency electromagnetic radiation.The activity (A) of a radioactive substance is the number of nuclei of that substance which decay each second.
1 becquerel is equal to 1 radioactive disintegration per second.
The number of nuclei decaying per second (i.e. the activity), A, is directly proportional to the number of active nuclei, N.
i.e.
or 
.The decay constant,
,
is equal to the fraction of a sample which decays per second.The half-life,
,of
a radioactive material is the time it takes for have of the active nuclei
present to decay.
A mole of a substance contains as many particles as 12 grammes of carbon-12.
This number is called Avogrado's number.
Nuclear Fission is the splitting up of a large nucleus into stwo smaller nuclei of similar size.
Nuclear Fusion is the joining of two small nuclei to form a larger nucleus.