© Gunda W. C. – 2017PHYSICS DIRECTORY FORFORM FOUR

© Gunda W. C. – 2017SUBJECT MATTERS TO COVER

© Gunda W. C. – 20171. WAVESFrequency - The measurement of a waves cycles per second. Its SI unit is hertz (Hz) Wavelength - The measurement of the rate at which the phase of a wave moves through space Velocity (Phase) of a Wave - The fraction of a wave cycle which has happened over a given period of time Period of a Wave - The duration of one cycle of a wave Types of Waves - Stationary, longitudinal, mechanical, transverse

© Gunda W. C. – 2017Waves . . .Stationary (Standing) Wave - A wave that remains in a constant position due to interference between two waves (ex resonance) Longitudinal Waves - Waves that have the same direction of vibration along their direction of travel (the vibration of the medium is in the same or opposite direction as the motion of the wave) Mechanical Waves - Waves which travel through materials (ex vibrating string, sound, seismic waves)

© Gunda W. C. – 2017TRANSVERSE WAVES

© Gunda W. C. – 2017TRANSVERSE WAVES[ BEHAVIOUR OF WAVES ] Interference - The superposition of two or more waves resulting in a new wave pattern (when two or more waves collide they create a new pattern, called an interference pattern) Diffraction - Is the apparent bending of waves around small obstacles and the spreading out of waves past small openings. Diffraction occurs with all types of waves

© Gunda W. C. – 2017PROPAGATION OF WAVES1. A certain wave has a period of 0.2 sec and a wavelength of 60cm. What is the velocity of the wave in cm/s? Given: Period of the wave, T = 0.2s Wavelength, λ = 60cm Frequency, f = ? Velocity, v = ?

© Gunda W. C. – 2017SOUND WAVESAudibility Range - The range of sound waves which can be heard by an organism Beats - Volume fluctuations due to the interference between sounds of different frequencies Reverberation - The persistence of sound in a particular space after the original sound is removed, it is caused when a large number of echoes build up and then slowly decay as the sound is absorbed by the walls and air Echo - A reflection of sound - A telephone earpiece converts electric currents into sound waves

© Gunda W. C. – 2017MUSICAL SOUNDPitch - The perceived frequency of a sound Loudness - The quality of a sound that is correlated to amplitude (the physical strength of a wave), which is heard by an organism and is measured in terms of a scale from quiet to loud Node - A point where the amplitude of a standing wave is minimum Anti-node - A point where the amplitude of a standing wave is maximum Fundamental (Frequency) Note - The lowest frequency or note in a harmonic series

© Gunda W. C. – 2017Musical sound . . .Harmonic Series - A series of notes which are formed on a string that travel in both directions along the string, reinforcing and canceling each other to form standing waves creating audible sound waves Overtones - A frequency higher than the fundamental frequency of a sound Resonance - The tendency of a system to oscillate with larger amplitude at some frequencies than at others Oscillation - The repetitive variation over time about a central point of equilibrium (ex pendulum, AC power) Amplitude - The magnitude of change in the oscillating variable with each oscillation within an oscillating system

© Gunda W. C. – 2017ELECTROMAGNETIC SPECTRUMElectromagnetic Spectrum - The range of all possible frequencies of electromagnetic radiation Types of Radiation - Ultraviolet, x-rays, gamma rays, infrared rays, visible light, beta particles, alpha particles UV (Ultraviolet) Rays - A form of electromagnetic radiation which is shorter than visible light, but longer than X-rays X-rays - A form of electromagnetic radiation which is shorter in wavelength than UV rays and longer than gamma rays Gamma Rays - A type of electromagnetic radiation of very high frequency (short wavelength) which are produced by subatomic particle interactions like radioactive decay. Can be used to kill cancer cells Infrared Rays - A form of electromagnetic radiation which is longer than visible light

© Gunda W. C. – 2017Electromagnetic spectrum . . .Visible Light - The portion of the electromagnetic spectrum that is visible to the human eye Beta particles - High energy, high speed electrons or positrons emitted by certain types of radioactive nuclei Alpha Particles - Consist of two protons and two neutrons bound together into a particle identical to a helium nucleus which is produced in the process of radioactive decay Uses of electromagnetic radiation 1. A mixed beam of α-particles, β-particles, and γ- rays enter a magnetic field at right angles to the direction of the beam. Draw the diagram which best represents the paths taken by the particles.

© Gunda W. C. – 2017Uses of electromagnetic radiation . . .

© Gunda W. C. – 2017APPLICATIONS OF ELECTROMAGNETIC WAVES IN DAILY LIFE…………………………………………………………………………………………………………………...............................................................................................................................................................…………………………………………………………………………………………………………………………………………………………………………………………………………………………………....…………………………………………………………………………………………………………………..

© Gunda W. C. – 20172. ELECTROMAGNETISMMAGNETIC FIELDS DUE TO A CURRENT-CARRYING CONDUCTOR How an electric current creates a magnetic field - Draw magnetic line patterns around a current …………………………………………………….……………………………………………………ELECTROMAGNETIC INDUCTIONElectromagnetic Induction - A process where an e.m.f is induced in a coil which is interacting with a magnetic field whenever the flux through the coil changes

© Gunda W. C. – 2017APPLICATIONS OF ELECTROMAGNETS…………………………………………………………………………………………………………………...............................................................................................................................................................…………………………………………………………………………………………………………………………………………………………………………………………………………………………………....…………………………………………………………………………………………………………………..

© Gunda W. C. – 2017LAWS OF ELECTROMAGNETIC INDUCTIONFaradays Law - Whenever there is a change in the magnetic flux linked with a circuit an electromotive force (e.m.f) is induced, the strength of which is proportional to the rate of change of the flux linked with the circuit Lenz’s Law - The direction of induced current is always such that it opposes the change producing it Magnetic Flux - A measure of the strength of a magnetic field on one side of a magnet. Its SI unit is V/sec Inductor - A coil of low resistance wire used to store magnetic flux and control an alternating current (AC)

© Gunda W. C. – 2017Continue . . .Eddy Current - Induced current loops circulating within a conductor Advantages of eddy currents - Useful in heating metals, electrical damping, crack detection, measurement of thickness of the material or coating, measurement of conductivity How eddy currents are produced - Produced when flux through a piece of metal changes, it induces an e.m.f. This induced e.m.f causes currents to flow around the metal piece in closed loops. The current is significant because the resistance of the path is very low How to minimize eddy currents - Using laminated cores, using magnetic materials with high resistivity

© Gunda W. C. – 2017Continue . . .Solenoid - A long thin loop of wire wrapped around a metallic core which produces a magnetic field when an electric current is passed through it. They are used as electromagnets Self Induction - The induction of a magnetic field by its own current Mutual Induction - The induction of a magnetic field by current in another circuit Factors affecting the magnitude of an induced e.m.f in a moving coil - Strength of the magnetic field, speed of rotation of the coil Transformer - A device which transfers electrical energy from one circuit to anther through the transformer’s coils

© Gunda W. C. – 2017Continue . . .Reason why high voltage is used for commercial transmission of electrical energy - It minimizes energy losses because high voltage provides lower current. From the equation Power = I2R, so the lower the current, the lower the power losses

© Gunda W. C. – 2017Continue . . .1. The figure shows a model of an electrical transmission system. AB and CD each represent a long length of cable each having a resistance of 4Ω. The current in AB is 0.1 A, find the:(i) Power lost by AB and CD Note that since AB and CD have the same resistance, so they will have the same current Given: I = 0.1 R = 4Ω P = ? Power lost due to resistance: P = I2R

© Gunda W. C. – 2017Continue . . .(ii) P.d across BD

© Gunda W. C. – 2017Continue . . .(iii) Current through the bulb

© Gunda W. C. – 20173. RADIOACTIVITYTHE NUCLEUS OF AN ATOMProtons - Positively charged particles of an atom which have a mass equal to that of a hydrogen atom Neutrons - Particles of an atom with an equal mass to protons that carry no charge Electron - A particle which carries a negative charge, it is smaller than protons and neutrons Radiation - A process in which energetic particles or waves travel through a medium or space

© Gunda W. C. – 2017NATURAL RADIOACTIVITYNaturally occurring forms of radiation - Alpha particles (α-particles), beta particles (β-particles), gamma rays (γ-rays) α-particles - Particles with low penetrating power which can be stopped by very thin aluminum foil, normal paper or by the human skin. They also have a limited range in the air because the ionize air β-particles - Particles with high penetration power which can penetrate many metals (or only a few cm of lead), can penetrate human tissue. They can travel long distances in air because they do not ionize air γ-rays - Rays with very high penetrating power (higher than β-particles) which can penetrate many metals (or only a few cm of lead) and can penetrate human tissue. They can travel very far in the air because they do not ionize air

© Gunda W. C. – 2017Continue . . .Half Life - The time required for half of the present number of atoms to decay Ionizing Radiation - Consists of subatomic particles or electromagnetic waves which are energetic enough to detach electrons from atoms or molecules, thus ionizing them Geiger-Mullar Counter - A particle detector that measures ionizing radiationDifferentiate between beta (β) particles and gamma (γ) rays

© Gunda W. C. – 2017Question 1. A radioactive element has an initial count rate of 1200 counts per minute measured by a scale and this falls to 150 counts per minute in 15 hours. (i) Determine the half life of the element Given: Co = 1200 counts per minute C = 150 counts per minute t = 15 hours n = number of half lives = ? t1/2 = ?

© Gunda W. C. – 2017Solution

© Gunda W. C. – 2017Continue . . .(ii) If the initial number of atoms in another sample of this element is 3.0x1020, how many atoms will have decayed in 25 hours? Given: Initial number of atoms, No = 3.0x1020 atoms Time, t = 25 hours Length of half life, t1/2 = 5 hours Number of half lives, n = ? Number of atoms decayed, N = ?

© Gunda W. C. – 2017Solution

© Gunda W. C. – 20172. Thorium disintegrates in the following manner

© Gunda W. C. – 2017(ii) Draw the graph of count rate against time for the following data, then determine the half life of thorium

© Gunda W. C. – 2017Continue . . .By looking at the graph we can see that the half life of thorium is 8 minutes. Since the original count was 40, we look at 20 to see at what time it occurs. Since it occurs at 8 minutes, the half life of thorium is 8 minutes. This is shown by the dotted linesARTIFICIAL RADIOACTIVITYDifferentiate between natural and artificial radioactivity - Natural radioactivity happens due to the properties of the substance causing it to decay over time, whereas artificial radioactivity is caused by the actions of humans adding neutrons to the atoms causing them to become unstable and decay Applications of artificial radioactivity - Particle accelerators, nuclear power

© Gunda W. C. – 2017RADIATION HAZARDS AND SAFETYPrecautions when handling radioactive material - Material should be stored in lead casing, package should be labeled appropriately, package should be handled carefully NUCLEAR FISSION AND FUSION Differentiate between nuclear fission and nuclear fusionNuclear Fission - A process whereby a large atomic nucleus is split into two smaller particles, releasing energy and radiation Nuclear Fusion - The process in which two or more atomic nuclei join together to form a single heavier nucleus Applications of nuclear fission - Nuclear power, research, nuclear bombs Applications of nuclear fusion - Hydrogen bombs

© Gunda W. C. – 20174. THERMIONIC EMISSIONCATHODE RAYSThermionic Emission - A process in which electrons gain sufficient enough energy to overcome the work function of the metal and are able to escape from the surface of the metal Cathode Ray - A stream of electrons in vacuum tubes (evacuated glass tubes) Properties of cathode rays - Produce fluorescence, are deflected by electric and magnetic fields, travel in straight lines, carry negative charge, posses kinetic energyCathode Ray Oscilloscope (CRO) - Uses of CRO - Measuring frequencies, measuring voltages, measuring phase differences, measuring small time intervals Main parts of a CRO - Electron gun, deflection system, fluorescent screen

© Gunda W. C. – 2017Continue . . .How a stream of electrons is produced in a CRO - They are released from the cathode by thermionic emission, then they are accelerated by the anode to a high velocity forming the stream of electrons Ensuring electrons produced do not accumulate at the source - The device uses anodes to accelerate the protons Ensuring electrons reach their range undeviated - A focusing anode is used Ensuring electrons travel without meeting other particles on their way to the target - The devices are evacuated so that the electrons do not collide with other particles Cathode Ray Tube (CRT) - Cathode Rays - Streams of electrons inside an evacuated CRT

© Gunda W. C. – 2017Continue . . .Uses of a cathode ray tube - Television Why cathode ray tubes are evacuated - So that electrons can travel without colliding with other molecules Effects when gas is maintained in a CRT - It will behave like an open circuit and when the potential difference (p.d) is strong enough, it will cause an electric spark. Also, an image will not be formed because cathode rays will not be present Role of high voltage - Provides high tension between electrodes which is used for acceleration of electrons Role of low voltage - To heat up the cathode Role of tungsten target - Used to absorb highly energetic electrons and to emit X-rays by converting kinetic energy of the electrons into electromagnetic waves

© Gunda W. C. – 2017X-RAYSProperties of X-rays - Travel in straight lines at the speed of light, cannot be deflected by electric or magnetic fields, can produce fluorescence, affect photographic film, penetrate matter (dependent on density of the matter), ionize gases, are diffracted by crystals Effects of X-rays on humans - Destroys body cells, causes mutation of DNA, can cause cancer, can destroy fertility How to produce X-rays - An accelerated electron beam is focused onto a target with a high melting point. The fast moving electrons collide with the targets atoms and excite them. This causes the electrons of the atoms to go to higher energy levels and jump back to lower energy levels, emitting X-rays (photons) Types of X-Rays - Hard, soft

© Gunda W. C. – 2017Continue . . .Hard X-Ray - An X-ray which can penetrate solid objects How hard X-rays are produced - Produced when a very high voltage is applied between electrodes which accelerates electrons which release X-rays when they hit the tungsten target Soft X-Ray - Ax X-ray which cannot penetrate solid objects

© Gunda W. C. – 2017Differentiate between X-rays and gamma (γ) raysDifferentiate between X-rays and white light

© Gunda W. C. – 20175. ELECTRONICSSEMICONDUCTORS Semiconductor - A material with electric conductivity due to electron flow which is an intermediate in magnitude between a conductor and an insulator Semiconductors commonly used in electronics - Silicon, germanium Doping (of Semiconductors) - Adding small amounts of impurities to semiconductors to improve their conductivity P-Type Semiconductor - A type of semiconductor which is obtained through doping which increase the number of positive charge carriers N-Type Semiconductor - A type of semiconductor where atoms are capable of providing extra conduction electrons to the host material which creates an excess of negative electron charge carriers

© Gunda W. C. – 2017Continue . . .P-Type Doping - Creates an abundance of electron holes which allows atoms to accept electrons from a neighbouring atoms covalent bond Extrinsic Semiconductor - A semiconductor which has been doped giving it different electrical properties than an intrinsic (pure) semiconductor Intrinsic (Pure) Semiconductor - A semiconductor which has not been doped and therefore has the natural electrical properties of the semiconductor Electron Hole - Is the concept of the lack of an electron at a position where one could exist in an atom

© Gunda W. C. – 2017Differentiate between conductors and semiconductorsDiode - A two terminal electronic component that conducts electric current in only one direction Junction Diode - How a junction diode works - Relies on the fact that current flows easily from P-type to N-type diodes. When P-type is connected to the anode it attracts electrons from the N-type, while the N-type attracts holes from P-type which closes the depletion layer. In the reverse direction the depletion layer will be widened

© Gunda W. C. – 2017Continue . . . Rectification - The process of converting an alternating current into a direct current Role a capacitor plays when used in - AC circuits, DC circuits AC Circuits - Used in amplifiers for separating AC from DC, in radios for tuning, and in rectification for smoothening DC Circuits - Charge storage when charging or discharging. When discharging a capacitor can act as an e.m.f source Transistor - A semiconductor device which is used for the amplification of current and voltage N-type Transistor - P-type Transistor -

© Gunda W. C. – 2017Continue . . . Principle of a transistor - It is made of two pieces of either N-type or P-type material with the other type in between them. The outer pieces are used as a collector and emitter while the middle piece is used as the base and is thinner than the outer pieces. During operation a small current is passed from the base to the emitter or its reverse. This small current starts a larger current from the collector to the emitter through the base or its reverseDifferentiate between NPN and PNP transistors

© Gunda W. C. – 2017Single stage amplifier

© Gunda W. C. – 20176. ELEMENTARY ASTRONOMYINTRODUCTION TO ASTRONOMY Astronomy - The scientific study of the objects in the universe like stars, galaxies, planets and comets Asteroids - A collection of particles of various sizes which revolve around the sun in a way similar to planets Comets - An asteroid which glows brightly in space Stars - Heavenly bodies which produce their own energy (light and heat) Planets - Heavenly bodies that cannot produce their own energy and revolve around stars Meteor - Asteroids that enter into the Earth’s atmosphere and burn up completely before reaching the surface of earth Meteoroid - Solid object moving in interplanetary space and is smaller than an asteroid

© Gunda W. C. – 2017Continue . . .Lunar Eclipse - Occurs when the moon passes behind the earth such that the earth blocks the sun’s rays from striking the moon Galaxy - A massive gravitationally bound system of stars and gases. Our galaxy is the Milky Way Solar system Differentiate between a star and a planet - A star is capable of emits its own energy through the fusion of hydrogen atoms, a planet creates energy internally through geothermic actions Solar System - A system consisting of the sun and all of the astronomical objects bound to it by gravity Gravity - The force of attraction that causes bodies to fall towards heavier bodies like planets or stars. This is the force that causes planets to revolve around the sun

© Gunda W. C. – 2017Continue . . .Heliocentric Theory - The sun is at the centre of the solar system and all other bodies including the Earth revolve around it in circular orbits while rotating about their axes. This is a true theory Geocentric Theory - Claims that the Earth is at the center of the solar system and the sun and other planets revolve around Earth. This is not a true theory Basic trends of the planets - Average temperature of the planets - Average temperature decreases as distance from the sun increases because they are further away from the heat source (sun) Average densities of the planets - Densities generally decrease from Mercury to Saturn and then increase from Saturn to Neptune. Earth has the highest density because its core is made of iron and nickel, while Saturn has the lowest density because it is made of gases

© Gunda W. C. – 2017Continue . . .Length of revolutions of the planets - Period of revolutions increases as distance from the sun increases Why an astronaut… Needs a spacesuit to prevent his blood from boiling - The body temperature of the astronaut is enough to boil his blood because there is nearly zero atmospheric pressure Floats without falling - There is almost no gravitational force so he does not fall towards anything Uses jets of gas to move instead of swimming like in water - He cannot swim because there is no matter to push against, in order to move forward he needs to exert a force on surrounding matter

© Gunda W. C. – 2017Continue . . .Mercury has no atmosphere and is the closest planet to the sun Neptune is the farthest planet from the sun (Note that Pluto is no longer considered a planet) Mars is the closest planet to the Earth Saturn is surrounded by rings Jupiter is the largest planet in the solar systemVenus is the brightest planet in the solar system Constellation - A certain area in the celestial sphere that can be used for navigation based on the perceived pattern formed by prominent stars in the night sky

© Gunda W. C. – 2017THE EARTH AND THE MOONTides - The rise and fall of sea levels caused by the effects of gravitational forces by the moon, sun and the rotation of the earth Mass and weight on the Earth and Moon - Mass never changes since it is not affected by gravity (it will be the same on the Moon and on Earth. Weight will change because weight is affected by gravity (it will be heavier on Earth and lighter on the Moon) Question 1. The distances of Jupiter from the sun 7.8 x 108km and one year on Jupiter is equivalent to 12 years on earth. Calculate the: (i) Distance of its path in one year

© Gunda W. C. – 2017Solution Given: Radius of the path, 7.8 x 108km Circumference of a circle: C = 2πrNote that the distance of its path is the circumference of a circle, since Jupiter has a circular orbitStep 1: Calculate circumference C = 2πr)C = 2 x π x ( 7.8 x 108) C = 4.903 x 109 km (ii) Speed of the planet in km per hour Given: Distance = 4.903 x 109km Time = 12 years x 365 days x 24 hours = 105,120 hours

© Gunda W. C. – 2017Solution . . .

© Gunda W. C. – 20177. GEOPHYSICS(Found in the Geography study guide)