CHAPTER 1 INTRODUCTION INTRODUCTION TO PHYSICS
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Physics is a branch of science that studies phenomena in nature related to energy, the structure and properties of matter, and the relationship between them. Physical quantity A quantity that can be measured .
A Base quantity is a quantity that cannot be defined in terms of other quantities. The base quantities are length, mass, time, electric current and temperature . Standard International Unit (S.I.) was introduced to facilitate communication and to coordinate international trading activities.
Extremely large or small values may be written in scientific notation, A x 10 n, where 1 ≤ A < 10, and n is an integer. physical quantities, e.g. pico, Prefix is a multiplying factor used to represent large or small physical nano, micro, mili, centi, kilo, mega, giga and tera. A derived quantity is a quantity that is obtained by a combination of basic quantities by multiplication, division or both. A scalar quantity is a physical quantity that has magnitude only. only. A vector quantity is a physical physical quantity that has has magnitude and direction. Measurement is the process of determining the value of a physical quantity values using scientific instrument. Precision is the ability of a measuring instrument to measure in a consistent manner with little or no relative deviation in the readings obtained. Accuracy in measurement is the degree of closeness of a measurement value to the actual value. Sensitivity is the ability of an instrument to measure slight changes in the physical quantity being measured. Systematic error causes all readings to be either too big or too small. Random error causes readings to disperse about the actual reading. Parallax error is a measurement error that happens when one reads a scale’s reading from a wrong position. Making an inference means interpreting or explaining factors as a result of an observation. Example: the period of a simple pendulum is affected by its length. Hypothesis is a general statement that attempts to relate two or more variables. Example: the longer the length of a simple pendulum, the longer the period of its oscillation.
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Variable is a physical quantity that must be considered in order to describe an observation. Example: Example: The period of oscillation of a simple simple pendulum and the length of the thread of the pendulum. Manipulated variable is a physical quantity whose values must be determined before the experiment is carried out. Example: Length of the thread of the pendulum. Responding variable is a physical quantity that depends on a manipulated variable and is obtained during the experiment. Example: The period of oscillation. Fixed variable is a physical quantity that must be fixed throughout the experiment. Example: mass of the bob, gravitational gravitational acceleration.
Checklist of methods of plotting graphs ( ASPCGI): axes, scale, plot, curve, gradient and intercept. A graph represents the average value of the readings of an experiment and provides a visual relationship between variables under investigation.
Analy Analysin sing g inform informatio ation n from from the graph graph to find find data patterns , the relati relations onship hip between between variables involved and to formulate generalisation of a particular principle or law of physics. When a straight line that has a positive gradient and that passes through the origin is obtained, the equation that can be deduced is y = mx This shows that y that y is directly proportional to x to x,, and m is the gradient of the line. When a straight line that does not pass through the origin is obtained, the equation that can be deduced is y = mx + c This shows that y that y has a linear relationship with x with x,, and c is the intercept for the line on the y-axis. y-axis. in y,, ∆ y, y, divided by the change in x in x,, ∆ x. x. The gradient of a line is the change in y Gradient =
∆ y ∆ x
the y-axis, -axis, i.e. the value of y y when x when x = 0. Y-intercept is the point where the line crosses the y
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CHAPTER 2 FORCE & MOTION
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Linear Motion is the motion of an object in a straight line . Kinematics is the study of the of motion objects without considering the forces that cause the motion of the object . Distance is the total length of the path covered by a moving object. Displacement is distance from one point to another in a particular direction. Speed is rate of change of distance. Unit m s-1 Velocity is the rate of change of displacement. Average speed is total distance moved divided by total time taken. Average velocity is total displacement divided by total time taken. Acceleration is rate of change of velocity. Unit m s-2 a=
v−u t
Equations of linear motion with uniform acceleration are as follows : 1 v = u + at s = ut + at 2 v 2 = u 2 + 2as 2 Dynamics is the study of the motion and of the forces that cause the motion of that body. Inertia is the resistance of an object to change of its motion. Inertia is non-physical quantity. Mass of an object is the quantity of matter in that object. Newton’s First Law of motion states, if no external force is acting on an object, it will, if stationary remain stationary, if moving keep moving at a steady speed in a straight line. Momentum of an object is defined as a product of mass and its velocity. Unit kg m kg m s-1 p = mv
Principle of conservation of momentum states that when two or more objects act on each other, their total momentum remains constant, provided there are no external forces acting on the system. (m1u1 + m2u2 = m1v1 + m2v2)
Force acting on an object can cause changes to its size, shape, and state of rest, velocity, and direction of motion of the object. Newton’s second law of motion states that force acting on an object is directly proportional to the rate of change momentum of the object in the same direction. F = ma
Impulse is the product of force and time for which the force acts during collision
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Impulsive force is the force that acts on an object within a very short time such as during a collision. F =
mv − mu t
Gravitational attractive force is the pull (force) of the earth on objects and it acts towards the centre of the earth
An object is in free fall when it falls under the influence of gravitational attractive force without the influence of other forces. (A free fall is situation whereby an object falls under the influence of gravitational attractive force only). Gravitational acceleration acceleration is the acceleration of an object which falls freely. Weight of an object is the gravitational force acting on it. Or
W = mg ( mg (m = mass, g mass, g = = gravitational acceleration) An object is in equilibrium if the resultant of forces acting on it is zero. Newton’s Third Law of Motion states that for every force there is an opposite an equivalent force against it. A resultant force is a single force that represents in magnitude and direction two or more forces acting on an object. Resolving a force is replacing a single force by a pair of perpendicular forces provided that the resultant of the two forces is equivalent to the single force. Work done by constant force to move an object is equivalent to the product of the magnitude of its displacement and the components of the force, which is in the direction of the displacement. W = Fs
Energy is defined as the capacity of a system to do work. Gravitational Gravitational Potential Energy is defined as energy obtained by an object due to its position. E = mgh
Elastic Potential Energy is defined as energy obtained by object due to its state (extension or compression) 1 W = Fx 2
Kinetic Energy is defined as energy attained by an object due to its motion. E =
1 2
mv 2
Conservation of Energy states that energy cannot be created nor destroyed but changes from one form to another. Elasticity of a material is its ability to return to its original form and size when the force acting on it is removed.
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Hooke’s law states that the extension of an elastic spring is directly proportional to the force acting on it provided that the limit of elasticity is not exceeded. Spring constant is defined as force per unit extension of a spring. F k = x A soft spring has a smaller k smaller k value value whereas a stiff spring has a larger k larger k value. value.
The work done when extending or compressing an elastic material is given by W = 12 Fx The strength of a material is the ability of the material to withstand external forces before it breaks or snaps. Rattan is a strong but not rigid material. Concrete is both strong and rigid. Rigidity is the ability of a material to withstand external forces acting on it without changing its size or shape. Glass is a rigid but not a strong material.
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CHAPTER 3 FORCE & PRESSURE
The basic unit of matter is a particle. Matter normally exists in three states; solid, liquid and gas. The forth state is plasma. Kinetic theory of matter. m atter. (a) Matter consists of discrete particles known as atoms, molecules or ions.
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(b) The particles are always in random motion. (c) Attractive force and repulsive force exists between the particles. The attractive force occurs when two particles move further from each other, whereas the repulsive force occurs when the particles are nearer to each other. Density is defined as the mass per unit volume of a material. m
ρ
=
v Factors that affect density are temperature, impurities and pressure. Oil floats on water because its density is less than the density of water. On the other hand, a stone sinks in water because its density is higher than that of water. Surface tension refers to the force that acts at the surface of a liquid and causes that surface to behave like an elastic skin. Cohesive force is the attractive force between molecules of the same materials. Adhesive force is the attractive force between molecules of different materials. Pressure acting on a surface is defined as the perpendicular force per unit area. F P = A Pressure in a liquid is defined as the product of the depth in the liquid, the density of the liquid and the acceleration due to gravity. P = hρ g
The atmospheric pressure is the pressure that the atmospheric layer exerts on the surface of the Earth. Atmospheric pressure = 1 atm = 760mm Hg.
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Archimedes principle states that when a body is (partially or totally) immersed in a fluid, the upthrust on the body is equal to the weight of the fluid displaced. Weight of object = Upthrust
Pascal’s Principle states that in a confined fluid, externally applied pressure is transmitted uniformly in all directions in the liquid.
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Bernoulli’s Principle states that at any point in where the velocity of fluid increases, its pressure decreases. On the other hand, when the velocity of the fluid at that point decreases, its pressure increases.
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CHAPTER 4 HEAT
Temperature (T) is a measure of the degree of hotness. Heat is the energy transferred from a hot object to a cold one.
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Two objects are in thermal equilibrium when the rates of heat flow between the objects are equivalent or the net rate of transfer of heat is zero. The thermomet thermometric ric property property is the the phy physical sical prop proper erty ty of a subs substa tanc ncee that that chan change gess with with temperature.
Lθ − L0 The temperature on the Celsius scale is given by the formula : θ = L100 − L0
× 100
o
C
substance is the quantity of heat required to raise the Specific heat capacity capacity, c of a substance temperature of 1 kg of the substance by 1oC. Heat that is absorbed or released by an object is Q
= mcθ
If the heat supplied by an electrical heater is Pt is Pt , then Pt = mcθ Latent heat is the quantity of heat absorbed or released when the state of matter changes at constant temperature. Q = ml Specific latent heat heat of fusion of a substance is the quantity of heat required to change 1 kg of the substance from a solid state to a liquid state without any change in temperature. Specific latent heat heat of vaporization of a substance is the quantity of heat required to change 1 kg of the substance from a liquid state to a vapour state without any change in temperature. Evaporation is the conversion of liquid to vapour that occurs occurs at the surface of of the liquid at any temperature.
liquid to vapour at the boiling boiling point. Boiling is the conversion of liquid Boyle’s Law states that for a given mass of gas, the pressure of the gas is inversely proportional to its volume if the temperature is constant. p1V 2 = p 2V 2 Pressure Law states that for a given mass of gas, the pressure is directly proportional to its p1 p 2 = thermodynamic temperature if the volume of the gas is constant. T 1 T 2 Charles Law states that for a given mass of gas, the volume of the gas is directly proportional
to its thermodynamic temperature if the gas pressure is constant.
The Universal Gas Law is given by:
p1V 1 T 1
=
p 2V 2 T 2
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V 1 T 1
=
V 2 T 2
CHAPTER 5 LIGHT
The reflection of light by a plane or curved mirror obeys the Laws of Reflection. (a) The incident incident ray, normal normal and reflected reflected ray lie in the the same plane. plane. (b) The angle of incidence incidence is equal to the angle angle of reflection. reflection. Plane mirrors produce images, which are of the same size as the object, virtual and laterally inverted. The image distance is equal to the object distance.
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Convex mirrors produce images, which are always virtual, upright and diminished (reduced in size) whereas concave mirrors produce images whose properties are dependent of the location of the object from the mirror.
Convex Mirror
1- A ray parallel to the principal axis is reflected as if it it came from F. 2- A ray which appears to came from F is reflected parallel parallel ncipal to pri axis. 3- A ray which appears to come from C strikes the mirror at right right angles and returns along along the same path away from C.
F
C
concave mirrors produce images whose properties are dependent of the location of the object from the mirror.
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Determining the position and characteristics of an image with a Ray Diagram Concave Mirror 1- A ray parallel to the principal principal axis is reflected reflected through F. 2- A ray passing through F is reflected parallel to the principal axis. 3- A ray passing passing through through C strikes strikes the mirror mirror at right angles angles and returns along the same path through C.
Object
C
F
4- The intersection intersection of the lines is is the position of an image image
Refraction of light is said - to have have occu occurred rred when when ther theree is a change change of of direct direction ion of of a ray of of light light when when it ente enters rs another transparent medium with a different density. - The bending bending of of light light when when it enters from one medium medium to another another with with differen differentt density density
The change of the speed of light causes a change in the direction of its propagation and consequently, refraction is said to have occurred. Snell’s Law states that the ratio of the sine of the angle of incidence, i , to the sine of the angle of refraction, r is r is a constant. This ratio is also known as the refractive index, n. n=
sin i sin r
The angle of refraction of a ray of light when it propagates from one medium to another medium depends on: (a) the type type of medium( medium(refractiv refractivee index) index) (b) the angle angle inciden incidence. ce. The critical angle, c, is the angle of incidence of light, moving from a denser medium towards a less dense medium where the angle of refraction is equal to 90o. If the less dense medium is air, then the refractive index , n of the denser medium is given by, 90o
Air
n=
1 sin c
Liquid-Y C
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When a ray of light propagates from a denser medium to a less dense medium total internal reflection is said to occurred when the the angle is incidence is greater than the critical angle. Convex lenses are thicker in the middle section and converge rays that pass through them.
f Concave lenses are thinner in the middle section and diverge rays that pass through them.
F f The focal length ( f ) is the distance from the centre of the lens to its focal point.
The power of a lens is the reciprocal of its focal length in metres. The dioptre (D), is the unit used to measure the power of a lens. P
=
1
f
The images formed by a concave lens are always virtual, upright and diminished (reduced in size) whereas the images formed by convex lens depend upon its object distance from the lens.
The lens formula and linear magnification are given by: Lens formula,
1 f
1
1
u
v
= +
Linear magnification, m =
v u
Lenses are used in cameras to form images which are real, inverted and diminished (reduced in size).
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The astronomical telescope consists of a low power objective lens and a high power eyepiece lens. The compound microscope m icroscope consists of two thin high-power lenses (with very short focal lengths). The slide projector uses a convex lens to produce images on a screen which are real, inverted and magnified.
The magnifying glass also known as a simple microscope consists of a single low power convex lens. When the object distance is less than its focal length, it forms images which are virtual, upright and magnified (increased in size). Opticians use plane mirrors to test the eyesight of their short-sighted clients. Dentist use concave mirrors to examine the teeth of their patients. The principle of total internal reflection is applied in the construction of prismatic periscopes and binoculars. Fibre optics are used in endoscopes to enable surgeons to view the internal organs of their patients during an operation. In the world of the telecommunications, information is transmitted rapidly with the use of light along optical fibres. The Hubble space telescope is an example where we have combined the properties of light with modern technology to enable mankind to explore and gather more information about our universe.
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CHAPTER 6 WAVES
Vibration is the to and fro motion following a fixed path. Free vibrations are the vibrations of a system at its natural frequency without external disturbance.
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Damping/attenuation is caused by dissipative force such as friction or air resistance resulting in loss of energy from the vibrating system in the form of heat. Damped vibrations are the vibrations of a system where the amplitude decreass with time due to resistive forces. Forced vibrations are the vibrations of a system caused by external alternating forces. Amplitude is the maximum displacement of an oscillating object from its equilibrium position. Frequency is the number of complete vibrations per second. Period is the time taken for one complete oscillation. Relation between period and frequency is T =
1 f
Natural frequency is the frequency of an oscillating system without influence of any external force.
amplitude when Resonance is the condition of a vibrating system responding with maximum amplitude the frequency of the driving force coincides with the natural frequency of the system. Waves can be produced by an oscillating system such as the vibration of a motor or a tuning fork. Wave front is a line or a surface on which the particles of the medium vibrate with the phase. (Locus of points in the same phase)
Longitudinal waves are waves in which the particles of the medium vibrate in the same direction as the direction of propagation of the waves.
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medium vibrate perpendicularly to Transverse waves are waves in which the particles of the medium the direction of propagation of the waves.
Wavelength is the distance between two adjacent points along a wave which are in phase.
Wavelength (transverse wave) – distance between two consecutive crest / trough Wavelength (longitudinal wave) – distance between consecutive compression / rarefaction
Relation between velocity, frequency and wavelength is v = f λ λ
Refraction of water wave occurs because of the change in its speed and its direction of propagation when it travels through different depths of the water.
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Diffraction of water wave occurs when it passes through a small aperture or small obstacle. Diffraction of waves is the spreading of the wave when the wave bends after crossing an obstacle.
Interference of waves is the constructive and destructive superposition of waves from two coherent sources.
Constructive interference is the superposition of two waves which are in phase to form a resultant wave with maximum amplitude. (antinode) Destructive interference is the superposition of two waves which are out of phase to form resultant wave with zero amplitude. (node) Two wave are in phase if they are of the same frequency and are at the same place in their oscillation. (e.g. the crest of a wave meets the crest of another wave)
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They are out of phase if their displacement are exactly opposite. (e.g the crest of a wave meet the trough of another wave) The principle of superposition states that the resultant displacement of two waves at a certain point is the sum of the displacements of the two waves.
Two coherent light rays possess a fixed phase difference. Polarization is a phenomenon of waves which can be observed in the transverse waves but not in the longitudinal waves. Wave length, λ can be determined from the interference pattern by the formula: ax
λ =
D Where a = distance between two two coherent sources sources λ = wavelength x = distance between two consecutive node (or antinodes) lines D = Distance from the two sources to the point of measurement of x Sound is a longitudinal wave. A human being is able to hear sound having a range of frequency from 20 Hz to 20 kHz (audio frequency) Sound waves with frequency exceeding 20 kHz are known as ultrasonic waves. Echo is formed sound waves are reflected from a hard surface.
A louder sound is has a larger amplitude. Light is a transverse wave. Monochromatic Monochromatic light is a light wave with a fixed frequency or a fixed wave length.
Wave length of a monochromatic light, λ can be determined with a diffraction grating by the formula nλ = d sin θ n of an electrical field and a magnetic field Electromagnetic Electromagnetic waves are waves consisting of oscillating perpendicularly to each other. Electromagnetic Electromagnetic wave spectrum consist of radio waves, microwaves, infrared light, visible light, ultra-violet light, x-rays and gamma rays.
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CHAPTER 7 & 8 ELECTRICITY & ELECTROMAGNETISM
Electric current , I is I is the rate of flow of electric charge. I =
Q
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t
Electric field is a region in which which any charged body will experience an electrical force acting on it. Potential difference between two points is defined as work was done done to move a unit unit charge between two that points. Ohm’s Law states that the current flowing through a conductor is directly proportional to the potential difference across the conductor, provided that its physical condition and temperature remain constant.
V across a conductor to the current, I current, I Resistance, R the ratio of the potential difference, V across flowing through it. Superconductor is material which can a current with out resistance.
In a series circuit, the same current passes through each resistor but the potential difference is different. In a parallel circuit, different currents passes through each resistor but the potential difference is same. Electromotive force , (e.m.f.) of an electric source is electric energy supplied when 1 C of charge flows through it. Potential difference is equal to the amount electric energy transferred when 1C of charge flow between two points.
r of a cell resists the flow of current in the cell. Internal resistance , r of E − V = Ir
When charge, Q flowing between two points at potential difference, V the V the electric energy transferred is W = QV Electric power is the rate at which energy is transferred. P =
QV t
Efficiency of electrical appliances
=
Output power Input power
× 100%
Electromagnet consists of a solenoid with a soft iron core and is magnetised when a current is passed through it.
The direction of the magnetic field produced by the current in a straight wire can be determined by the Right-Hand Grip rule. The strength of the magnetic field produced by a solenoid depends on : (a) the number of of turns in the coil per unit distance. distance.
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(b) the magnitude magnitude of the current. current. (c) the material material in the core core of the solenoi solenoid d Electromagnetic Electromagnetic induction is the production of current in the conductor in a region of varying flux of a magnetic field.
In electromagnetic induction, e.m.f. is induced in the conductor when a conductor is moved so as to cut the flux of a magnetic field. Faraday’s Law states that the e.m.f. induced in a conductor is proportional to the rate at which the conductor cuts through the magnetic field lines. Lenz’s Law states that an induced current always flows in such a direction that it will oppose the change which is causing it. Fleming’s Right-Hand Rule can be use to determine the direction of the induction current
produced (used for generators.) Thumb ( motion )
First finger ( Field )
Center finger ( induced current )
Fleming’s Left-Hand Rule can be use to determine the direction of the force acting or the
motion of the conductor. (used for motors)
First Finger ( Field ) Thumb ( Thrust force )
Centre Finger ( Current )
Effective Value for an a.c. is equal to the direct current that produces heat at the same rate as that of the alternating current in a resistor. The effective value also known as root-meansquare value of the a.c.
The relation between peak value and root-mean-square value is:
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V rms
=
V 0 2
Moving Coil Meter can only be used to measure d.c.. Moving coil meter can be changed to become ammeter and voltmeter by adding a shunt and a multiplier respectively. Hot-Wire Meters and Moving Iron Meters are used to measure a.c. and d.c.. Step-Up Transformer is used increase a.c. voltage, Step-Down Transformer is used to decrease a.c. voltage.
Turns Ratio of the transformer: V S V P
=
N S N P
Energy is lost from a transformer is because of the coil resistance, eddy currents, flux leakage and the magnetizing and demagnetised of the core. The National Grid system is the network of cables and substation to transfer electric energy from power stations to other places. Power Loss during transmission of current power through the cables: P = I 2 R
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CHAPTER 9 ELECTRONICS
Thermionic emission is the emission of electrons from the surface of a heated metal.
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Cathode Cathode rays is a beam of high energy electrons emitted from a heated metal surface (cathode) in a vacuum tube that contains a cathode and an anode. A very high voltage has to be applied across the cathode and anode. EHT (Extra High Tension) is very high voltage that exceeds 1 000 V (1 kV)
The properties of cathode rays that can be studied by the Maltese Cross Tube, Deflection Tube and Perrins Tube: Properties of cathode rays (a) (a) Move Movess in a straight line (b) Has momentum and energy (c) Produces phosphorescence when it strikes a fluorescent material. (d) Negatively Negatively charged and and deflects towards towards the positive plate magnetic field and the sign of its charge can be verified verified using Fleming’s Fleming’s (e) (e) Defl Deflec ecte ted d by a magnetic Left Hand Rule. Cathode Ray Oscilloscope (CRO) consists of an evacuated glass tube and contains 3 main parts: (a) Electr Electron on gun gun (b) Deflectio Deflection n system system (c) Flouresce Flourescent nt screen screen
The energy of an electron (eV) converted to kinetic energy in a beam of cathode rays is given by: eV =
1 2
The CRO is used to (a) Measure Measure dc and and ac voltage voltagess (b) Measure short time intervals intervals (c) Display Display wave wave form formss
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mv 2
Semiconductor materials are solids that have values of electrical resistance between that of conductors and insulators. Charge carriers in semiconductors are electrons that are negatively charged and holes that are positively charged. Doping is the addition of a small amount of impurities (donor atoms and receptor atoms) into the lattice structure of a pure semiconducting material to increase its electrical conductivity. Forward-bias, the p-type of the diode is connect positive terminal and the n-type is connected to the negative terminal of the battery. Reverse-bias, the p-type of the diode is connected negative terminal and the n-type is
connected to the positive terminal of the battery. n-type semiconductors semiconductors are produced when a small amount of pentavalent material ( donor atoms) such as antimony, arsenic and phosphorus is doped into the semiconducting material that has only 4 valence electrons and this results in the excess of electrons when covalent bonds are formed. p-type semiconductors are produced when a small amount of trivalent material (receptor atoms) such as boron, gallium, and indium is doped into the semiconducting material this results in a lack of electrons when covalent bonds are formed. semiconductor diode is formed by combining p-type and n-type semiconductors. A semiconductor p-n junction is the region at which a p-type and n-type meet. A diode only allow one direction current conducts current from the anode to the cathode through the junction when the diode is forward biased. If the diode is reverse biased, current cannot flow through it.
A diode functions as a rectifier. Rectification is the process of converting alternating current (ac) to direct current (dc).
A capacitor is used to smoothen the current in a half-wave and full-wave rectification circuit. A transistor has three electrodes. (a) Emitte Emitter, r, E – supplies charge carriers to the collector. (b) (b) Base Base,, B – a thin layer sandwiched in between the emitter and collector to control the flow of charges. (c) (c) Collec Collector tor,, C – receives charge carriers from the emmiter. A npn transistor is produced when a p-type semiconductor is sandwiched between two ntype semiconductors. A pnp transistor is produced when a n-type semiconductor is sandwiched between two ptype semiconductors.
A transistor can function as an automatic switch and an amplifier. An integrated circuit (IC) is a small and compact electronic circuit in a silicon chip or micro chip.
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A logic gate is a switch or electronic device that has one or more inputs but only one output.
The basic logic gates are the AND, OR and NOT gate. A
A
AND gate
Y
OR gate
Y
B
B
A
Y
NOT gate
Gates formed by the combination of basic gates are the NAND, NOR, XOR and XNOR gates. The Boolean expression is used to summarise the operation of logic gates. The Half Adder is an electronic circuit that can perform the addition of two single digit binary numbers. The Half Subtractor is an electronic circuit that can perform the subtraction of two single digit binary numbers. The flip-flop circuit is an electronic circuit that (a) (a) cons consist istss of two two NOR gates (b) as two stable conditions conditions that are interchangeable interchangeable and can be repeated. repeated. (c) Has two inputs inputs obtained obtained from the the previous previous outputs. outputs. (d) Has two outputs outputs which have opposite opposite logic conditions. conditions. (e) Can remember the previous input states.
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CHAPTER 10 RADIOACTIVITY
Proton number of an element is equal to the number of protons in one atom of the element.
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Nucleon number is equal to the total number of protons and neutrons in one atom of an element. Radioactivity is decay of an unstable nucleus by emiting radiation (such as alpha particles, beta particles and gamma rays) to become a more stable nucleus.
Alpha particle, α is the helium nucleus and consists of 2 protons and 2 neutrons. During alpha decay: (a) an alpha alpha partic particle le is emitted emitted (b) proton proton number number is reduced reduced by by 2 (c) nucleon nucleon number number is reduce reduced d by 4 Beta particle, β particle, β is a very fast movintg electron. During beta decay: (a) a beta parti particle cle is emitte emitted d (b) proton proton number number increases increases by 1 (c) nucleon nucleon numb number er unchang unchanged ed
Gamma rays, γ are electromagnetic waves with very high frequency. During gamma decay: (a) gamma gamma rays rays are emitte emitted d (b) no change in the proton number and nucleon number number Examples of detectors of radiation are: Geiger-Muller tube • • Cloud chamber • Spark counter • Gold leaf electroscope electroscope • Photographic film • Scintillation counter Activity of a radioactive sample is the number of decays per second or the rate of decay. Half-life of a radioisotope is the time taken for the activity to decrease to half its initial value, Isotopes are atoms which have the same number of protons but different number of neutrons. Radioisotopes are isotopes whose nuclei are unstable.
One a.m.u (atomic mass unit) is equal to the mass of one twelfth of a carbon-12 atom. Mass defect or loss of mass occurs in radioactive decay and nuclear reactions. Einstein’s mass-energy relationship states that mass and energy can change from one form to another, and the relationship is given by:
E
=
2
mc
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Nuclear Fission is the splitting of a heavy nucleus into two smaller nuclei when it is struck by a neutron.
Chain reaction is the continuous fission of nuclei and this occurs when the new neutrons produced by a fission splits another nucleus.
Critical mass is the minimum mass that is required for a chain reaction. Nuclear Fusion occurs when two lighter nuclei combined together to form a heavier nucleus and energy is released.
Harmful effects of radiation to human beings are: (a) Somatic effect – damage to body parts except reproductive organs. (b) Genetic effects – damage to cells in reproductive organs. Radiation dosage is the energy transferred to a substance. The unit for radiation dosage is gray, Gy. 1 Gy = 1 J energy transferred to 1 kg substance of substance. Nuclear Reactors Reactors Uranium rods are the fuel rods or the material for the fission reaction. Graphite core slows down the fast fission neutrons. Control rods control the rate of the fission reaction. The coolant in the reactors carries heat from the reactor to be used in the production of steam. Lead or concrete shield prevents the radiation from being emitted to the surroundings.
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