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Physics Form 4: Chapter 2 - Newton First Law of Motion (Inertia) Inertia is the tendency of an object to remain in its state of rest or of uniform

motion in a straight line . Law of inertia is also known as Newton's First Law of Motion Newton's First Law of Motion state that an object will in its state of rest or of

uniform motion in a straight line unless it is acted upon by a net external force.

Examples of effect of inertia:

When the cardboard is jerked quickly, the coin will fall into the glass.Explanation : The inertia of the coin resists the change of its initial state, which is stationary. As a result, the coin does not move with the cardboard and falls into the glass

because of gravity.

Pull slowly - Thread A will snap.Explanation:

Tension of thread A is higher than string B. Tension at A = Weight of the load + Pulling Force

Yank quickly - Thread B will snap.Explanation: The inertia of the load prevents the force from being transmittedto thread A,

hence causing thread B to snap.Physics Form 4: Chapter 2 - Force Acting on a Skydiver

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The parachutist has just jumped out of the aircraft, and is falling faster andfaster( accelerating ).As her speed increases , the air resistance increases . Theparachutist is now falling fast enough for the air resistance to equal her weight .Thismeans that the forces on her are in balance , so her speed stops increasingand stays constant - she has reached her terminal velocity . (Around 120 mph in thisposition - she can fall faster if she leans forward to go head first.)Time to open theparachute. This dramatically increases the air resistance, so the parachutist slowsdown greatly ( decelerates ).For a few seconds, the air resistance is greater thanher weight. As she decelerates, the air resistance decreases. She's slowed down,and now the forces are back in balance Her speed is constant again - she has a new ,much slower, terminal velocity . On the ground, her speed immediately drops to zero.Her weight downwards equals the ground's push upwards, so there she stays.

Physics Form 4: Chapter 2 - Safety Car Features

1. Safety belt - help to hold the passengers in their position during collisionto prevent them from being thrown forward due to inertia.2. Front and rear crumple zone - easily crushed to increase the time ofimpact.3. Shatter-proof windscreen - it will not break into pieces easily.4. Airbags - to increase the time of impact and to cushion the driver frombeing hitting the front of the car.5. Passenger safety case - reinforced to protect passenger.6. Collapsible steering - to increase the time of collision if the driver crashesagainst it.7. ABS braking system - to prevent the car from skidding if sudden brake isapplied.8. Headrests - prevent the passengers from suffering severe neck injury.

Padded dashboard - increases time interval of collision so that impulsive force isreduced.Physics Form 4: Chapter 2 - Principle of Conservation of Energy

9.

At the top of the hill, the cars possess the maximum quantity of potentialenergy. Potential energy is dependent upon the mass of the object and the height ofthe object. The car's large quantity of potential energy is due to the fact that they areelevated to a large height above the ground. As the cars descend the first drop, they lose much of this potential energy in

accord with their loss of height. The cars subsequently gain kinetic energy. Kineticenergy is dependent upon the mass of the object and the speed of the object. The train of coaster cars speeds up as they lose height. Thus, their original

potential energy (due to their large height) is transformed into kinetic energy

(revealed by their high speeds). As the ride continues, the train of cars arecontinuously losing and gaining height. Each gain in height corresponds to the loss of speed as kinetic energy (due to

speed) is transformed into potential energy (due to height). Each loss in height

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corresponds to a gain of speed as potential energy (due to height) is transformedinto kinetic energy (due to speed) .

Physics Form 4: Chapter 3 - Pressure

Application of pressure:

When the area is small, a moderate force can create a very large pressure.This is why a sharp knife is good at cutting things: when you push the verysmall area of the sharp blade against something, it creates a really largepressure.

Supermodel can damage floors by walking on then in high-heeled shoes. Thisis because the area of the heel is small, so you can easily create enoughpressure to cause a dent in the floor.

Camels have large feet to increase surface area of contact with sand.Pressure produced is small. This is why a heavy camel will not sink into sandwhile walking on dessert.

Physics Form 4: Chapter 3 - Application of Archimedes Principle (Plimsoll Line)

Plimsoll line is a mark on a vessel’s side indicating the maximum depth to which itmay be safely immersed when loaded with cargo.

The maximum safe loading depth varies with ocean regions and seasons. In thetropics the water is warmer and therefore less dense than in temperate regions, sowith the same load ships will float higher in cold regions than in the tropics. Summerand winter cause similar changes. The density of water is determined by the salinity of water at different locations A ship will submerge deeper in freshwater than that in sea water because the

density of freshwater is smaller. The ship can be loaded with heavier load in sea water than in freshwater.

Physics Form 4: Chapter 3 - Application of Archimedes Principle (Hydrometer)

Hydrometer is used to measure the density of liquid. The hydrometer works on the principle that a floating object displaces a

volume of liquid whose weight is equal to the buoyant force. Hydrometer will sink deeper in the less dense liquid but float higher in the

denser liquid.

Design of a hydrometerCharacteristic Explanation

Lead shots areadded to the base

To lower the centre of gravityof the hydrometer

So that, hydrometer can float

upright in a liquid.Thinner and longerglass tube is used

Will give a larger scaledistance and can detect smallchanges in the densities.

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Big bulb at thebase is used.

So that more liquid can bedisplaced

For calibration,hydrometer isallowed to float inlower density and

higher densityliquid

Liquid level in lower densityand higher density is marked.The space between the twomarks is divided into a number

of equal divisions that givedensity readings.

Physics Form 4: Chapter 3 - Application of Bernoulli Principle ( Aerofoil )

A cross section of a typical airplane wing will show the top surface to be more curvedthan the bottom surface. This shaped profile is called an aerofoil or airfoil. Due to this aerofoil structural design, the difference pressure below and above theaerofoil able to produce a larger lifting force.

According to Bernoulli Principle: Air moves with higher speed over the top of aerofoil. This creates a region of lower pressure over it and a region of higher pressure

below it. This difference in pressure produce a resultant force acting upwards on the

wings.Physics Form 4: Chapter 3 - Application of Bernoulli Principle (Spinning Ball)

According to Bernoulli Principle, a ball which spins in the same direction ofmoving air will increase the velocity of the ball. The moving air in the oppositedirection of the spin ball is slowed down. Higher velocity will produce lower pressure and vice versa. Because of this, the air pressure on one side is higher than that the other side.

It produces a resultant force acting from high pressure to low pressure. Therefore, a spin ball curves.

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Physics Form 4: Chapter 3 - Application of Bernoulli principle (WindSurfing)

The air flow over the sail causes an increase in pressure on the windward sideand a decrease on the leeward side Area of leeward side has a low pressure because of the high speed of the

wind. A resultant force acts in the direction of F.

This resultant force can be resolved into component to the right and left. The component to the right can be balanced by the surfer who pulls it to theleft. Therefore, there exists a resultant force to the front so that the surfer moves to

the front. Factors affect the resultant force is the strength of the wind and the shape of

the sail.

Physics Form 4: Chapter 4 - Explanation of Boyle's law by the kinetic theory:

At constant temperature, the average kinetic energy of the gas molecules isconstant.

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When the gas is compressed, the volume is decreased. Therefore, the numberof molecules per unit volume will increase. The rate of collision of the gas molecules with the wall of container will

increase. Thus, the pressure of gas increases.

Explanation of Charles law by the kinetic theory

When the temperature of a gas in an enclosed cylinder israised, the gas molecules receive heat energy and their averagekinetic energy increases.

This means that molecular velocity will increase and thefrequency of collision between the molecules and the wall of thecylinder also increases. Thus, the gas pressure increases.

Increase in pressure will cause the piston to be pushed upand this indicates that the volume of the gas has increased.

Physics Form 4: Chapter 5 - Reflection of Light on Plane MirrorRay Diagram

Characteristic of image formed

Virtual

Upright Laterally inverted Same size as the object As far behind the mirror as the object is in front of it.

Concave Mirror

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Convex Mirror

Principal axis is the line through the centre of curvature and the pole of themirror. Pole is the point where principal axis meets with mirror surface. Centre of curvature is the centre of sphere that the mirror forms part. Radius of curvature (r) is the radius of sphere. Principal focus is the point to which all rays parallel to the principal axis

converge or from which they appear diverge. Focal length (f) is the distance between the pole and the principal focus.

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Parallel reflected rays converge at focal point. Real focus since the reflected rays actually pass through it.

Parallel reflected rays appear to diverge from focal point. Virtual focus since the reflected rays do not pass through it.

Physics Form 4: Chapter 5 - Concave Mirror Ray Diagrams

Ray diagrams are constructed by taking the path of three distinct rays from a pointon the object:

X) a ray parallel to the principal axis reflected through F (the principal focus)Y) a ray passing through C which is then reflected back along its original pathZ) a ray passing through F, which is then reflected parallel to the principal axis

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S < F(Objectbetweenfocal pointand mirror)

Virtual Upright Magnified (larger)

S = F

(Object atfocal point)

Reflected rays are parallel andnever meet, so no image is formed. In the limit where S approaches F,

the image distance approaches infinity,and the image can be either real orvirtual and either upright or inverteddepending on whether S approaches Ffrom above or below.

F < S < 2F

(Objectbetweenfocus andcentre of

curvature)

Real Inverted (vertically) Magnified (larger)

S = 2F(Object atcentre of

curvature)

Real Inverted (vertically) Same size Image formed at centre of

curvature

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S > 2F(Objectbeyond

centre ofcurvature)

Real Inverted (vertically) Reduced (diminished/smaller) As the distance of the object

increases, theimage asymptotically approaches thefocal point In the limit where S approaches

infinity, the image size approaches zeroas the image approaches F

Physics Form 4: Chapter 5 - Convex Mirror Ray Diagrams

Ray diagrams are constructed by taking the path of three distinct rays from a pointon the object:X) a ray parallel to the principal axis reflected through F (the principal focus)Y) a ray passing through C which is then reflected back along its original pathZ) a ray passing through F, which is then reflected parallel to the principal axis

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Physics Form 4: Chapter 5 -Refraction of Light

Refraction is the phenomenon of light bending when it travels from onemedium to another medium. Refraction occurs because the velocity of light changes when it travels from a

medium into another medium.

The law of refraction states that:1. The incident and refracted rays are on opposite sides of the normal atthe point of incidence and all three are in the same plane.2. The ration of sin i / sin r is a constant. This constant is called refractiveindex.

Physics Form 4: Chapter 5 - Ray Diagrams of Convex Lens

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Ray Diagram Rules for Convex Lens

1. Any incident ray travelling parallel to the principal axis of a convex lenswill refract through the lens and travel through the focal point on the oppositeside of the lens.2. Any incident ray travelling through the focal point on the way to the lens

will refract through the lens and travel parallel to the principal axis.3. Any incident ray passes through the center of the lens will in affectcontinue in the same direction that it had when it entered the lens.

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Physics Form 4: Chapter 5 - Concave Lens Ray DiagramsConcave lens is a diverging lens. The image form is smaller than the object, virtualand upright. Concave lens always produce images that share these characteristics.The location of the object does not affect the characteristic of the image.

Waves

Physics Form 5: Chapter 1 - Barton's Experiment (Resonance) Resonance occurs when the forced frequency of an external agent equals the

natural frequency of the oscillating system. When resonance occured, it produces maximum amplitude of vibration.

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Physics Form 5: Chapter 1 - Shape of the Coastline due to Wave Refraction

In the centre of the ocean, the wavefronts are straight and parallel to eachother. This is because the water waves travel at uniform speed as the depth of thesea water is uniform.

When the waves reach the coast, the water is shallower. Wave speed is reduced and refraction occurs. The wavefronts are refractedand become closer to each other. Wavelength decreases. Refraction causes the wavefronts to be bent towards the normal.

Wave refraction causes wavefronts to parallel the shape of the coastline asthey approach shore. Wave refraction also causes wave energy to converge at cape and resulting

erosion. Wave energy diverges at bay and spreads out to a wider region, resultingdeposition of sand. Therefore, amplitude of waves at the bay is smaller than at thecape.

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Physics Form 5: Chapter 1 - Refraction of Sound Wave

During day, the layers of air near the ground is warmer than the layers of airhigher up. Air layer near the ground is less dense. Therefore, sound wave is bent toward the normal.

At night, the layers of air near the ground is cool faster than the layers of airhigher up. Air layer near the ground is denser. Sound travels faster in warm air than in cool air resulting increasing of

wavelength. When the angle of incidence is larger than the critical angle, total internal

reflection occurs. Therefore, the path of the sound curves reflects downwards and you can hear

the sound easily at night. Physics Form 5: Chapter 1 - Application of Reflection of Sound

Echoes are caused by the reflection of sound. A sound wave will continue tobounce around or reverberate until it has lost all its energy. A wave has someof its energy absorbed by the objects it hits. The rest lost as heat energy.

The phenomenon of the reflection of sound is used to determine the distancebetween the two objects, for example depth of seabed, depth of cave or widthof a valley. The type of sound used must be ultrasound.

Sonar Sonar (Sound Navigation and Ranging). Sonar is used to detect underwater

objects (corals / fishes) or to determine the depth of the water by means of anecho. Sonar equipment emits a high frequency sound signal which is reflectedby the object in the water. The reflected sound wave is received by the sonarreceiver. The time taken for the echo to return is used to determine the

distance of the object below the water surface.

Sonar waves of high frequency is used because it possesses more energy,

high penetration power and can travel further through water. Application of noise cancellation:

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1. Headphone - people working near aircraft or in noisy factories can nowwear these electronic noise cancellation headsets to protect their hearing.2. Cars - The way it works is that a microphone connected to the car stereosystem picks up all the sound inside the car, including music or such from thestereo. Then the noise-cancellation system subtracts the sound of the musiccoming from the stereo and produces noise-canceling sound waves that match

the frequency of unwanted sound.3. Aircraft - The system uses microphones to pick up the vibrations due to jet's engine in the cabin walls. It then analyzes the signals and generatescounter vibrations in the walls to produce a net result of zero vibrations.

Physics Form 5: Chapter 2 - Electric Charge

Candle in the electric field

Heat energy from the candle flame produces ionization of air molecules to formpositive and negative ions. Movement of positive ions which are heavier towards the negative plate

causes a bigger spread of the flame.

Negative ions which are lighter move towards the positive plate and causing asmaller spread of the flame.Physics Form 5: Chapter 2 - Electric Bell (Application of Electromagnet)

When the switch is pressed, a current flows through the solenoids and theelectromagnets attract a soft-iron plate. The striker hits the gong and a sound is produced. The movement of the soft-iron plate breaks the contact and the circuit is cut

off. The electromagnet loses its magnetism and the striker springs back to original

position.

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Physics

Form 5: Chapter 3 - Forces on a Current-carrying Wire

Explanation:

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The straight lines with arrows show the direction of the magnetic field betweenthe north and south poles. The circular lines with arrows show the direction of the magnetic field of the

current. When the two fields are in the same direction and they produce a stronger

combined magnetic field. When the two fields act in opposite directions and they produce a weaker

magnetic field. Interaction between the magnetic fields produce a catapult field. Thus, the wire

carrying current experiences a resultant force in the direction from the stronger tothe weaker magnetic fieldPhysics Form 5: Chapter 3 - Alternating Current Motor

The permanent magnets used have curved surfaces at its poles to create aradial magnetic field which has a uniform strength. The uniform magnetic field ensures that the force acting on the rectangular coil

is uniform. A pair of slip rings is used to ensure that the rotation of the rectangular coil is

always in the same directionPhysics Form 5: Chapter 3 - Electromagnetic Induction

Electromagnetic induction is the production of an electromagnetic force ,(e.m.f) in a conductor by changing magnetic field .

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Each time the straight wire cuts across the magnetic field or the permanentmagnet moves towards the solenoid, a current is induced in the coil and a deflectionis observed in the sensitive galvanometer. An induced e.m.f is produced in a conductor if the conductor is in a changing

magnetic field.Physics Form 5: Chapter 3 - Application of Electromagnetic Induction (Torchlight)

Electromagnetic induction is the production of induced current by changing magneticfield. By using kinetic energy of shaking hand, electrical energy is produced to powerthe flash light through electromagnetic induction.

Kinetic energy ------> Electrical energy

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A powerful permanent magnet such as neodymium magnet is used because ofsmall size with strong magnetic field. The permanent magnet is placed inside aplastic track which allow it to slide up and down. The shaking hands move the strong magnet to cut through the copper coils

causing electromagnetic induction.

The electrical energy produced is stored in a capacitor that can be chargedhundreds of thousands times. The bulb is an energy efficient ultra bright white LED that can produce a beam

of light for several minutes after shaking the moving magnet for 30 seconds.Physics Form 5: Chapter 3 - Moving Coil MeterMoving coil meter only measures direct current. It has a linear scale because thepointer deflection is directly proportional to the size of the current.

How moving coil meter works:

1. With the switch open, there is no current flow through the meter coil.

2. With no current flowing, the coil generates no magnetic field and the pointerstays at zero reading.

3. Close the switch and a current flows through the coil.4. The current creates a catapult magnetic field and a turning force acts on the coil.

5. The turning force rotates the coil and the pointer deflects across the scale untilthe hairspring produces an equal and opposing turning force on the coil.

As the current through the coil increases, the magnetic field generated around thecoil increases. The stronger the magnetic field, the larger the turning force of the coilto move the pointer .

Function of the hairspring:

With the use of hairsprings, the coil will return to its initial position when there is nocurrent. The springs will also tend to resist the movement of the coil when there iscurrent through the coil. When the attraction between the magnetic fields (from thepermanent magnet and the coil) is exactly equal to the force of the hairsprings, thecoil will stop moving toward the magnet.

Other features are used to increase the accuracy and sensitivity of this metermovement such as.

An iron core is placed inside the coil to concentrate the magnetic fields.

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Curved pole pieces are attached to the magnet to produce a radial magneticfield to ensure that the turning force on the coil increases steadily as the currentincreases. Using stronger magnet. Increasing the number of turns in the coil. Increasing the area of the coil. Using a weaker hairspring.

Physics Form 5: Chapter 3 - TransformerTransformer is an electrical device which increases and decreases an alternatingvoltage. Transformer only works with alternating current

How transformer works: A transformer works on the principle of electromagnetic induction. When the a.c voltage, V p is applied to the primary coil, an alternating

current flows through the coil. The soft iron core is magnetized in one way andthen the other. This causes a changing magnetic flux to pass through the secondary

coilproducing an a.c voltage V s .

Physics Form 5: Chapter 3 - Transmission of Electricity

Electricity is transmitted mainly through overhead lines or underground cables. Dueto the resistance of the transmission wires, there is always some loss of powerthrough the heating effect of current. The electricity transmission systems must bedesigned in ways which reduce this loss as much as possible.

High voltage transmissionElectricity generated in power stations is raised to a very high voltage fortransmission. This is to reduce the current flow to the transmission cables.

P loss = I 2R

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The power loss is proportional to the square of the current, thus a small currentgreatly reduces heat loss. As seen from the equation above, a small current can beachieved by using a high voltage. For example, if we double (×2) the transmissionvoltage, the current would be halved (×1/2), and the power loss would be reduced toa quarter, (1/2) 2 = 1/4, i.e. 25% of the original value.

Low Resistance Transmission WireWe see from the equation above that the power loss in the transmission wire P loss isdirectly proportional to the resistance R of the wire. The lower the resistance, thelower will be the power loss. Copper and aluminium are the most commonly usedmetals in transmission wires. They are very good conductors, cheap, resistant tocorrosion, and strong. The resistance of the transmission wire is lowered by makingthe wire thicker. Thicker wires have larger cross-sectional areas and therefore lowerresistance.

Electrical Transmission by Overhead Wire

Overhead lines are held high above the ground by metal towers called pylons. If youlook at a pylon carefully, you will see that the overhead lines are held by a stack ofdiscs hanging from the pylon. This stack of discs is a series of suspended insulatorswhich prevents the line from being electrically connected to the pylon. This prevents

the electrical leakage from transmission wire to the ground.Physics Form 5: Chapter 4 - Components of Cathode Ray Oscilloscope

Cathode ray oscilloscope, CRO is used: To display waveform of waves To measure the potential difference To measure short time interval To test electronic equipments

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A voltage applied to the x-plates can pull the electron beam side to side (along the x-axis), and a voltage applied to the y-plates can pull the electron beam up and down(along the y-axis). Vacuum inside the CRO tube is to allow electrons to move freely.

Physics Form 5: Chapter 4 - SemiconductorSemiconductor is a material where its electrical conductivity lie between conductorsand insulators. In semiconductors, thermal energy is enough to cause a smallnumber of electrons to escape from the valence band of atom to the higher energy ofconduction band, in which they are relatively free to move. The resulting gaps in thevalence band are called holes.

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Usually, semiconductors are made from semi-metal or called metalloid from thePeriodic Table.

Silicon is the most preferred material for semiconductors because: ease of availability low cost of processing

higher temperature range high resistivity than other counterparts low leakage current

Physics Form 5: Chapter 4 - The Doping of Semiconductor An extrinsic semiconductor is an improved intrinsic semiconductor with a small

amount of impurities added by a process, known as doping, which alters theelectrical properties of the semiconductor. Doping process can improvesemiconductor's electrical conductivity. Doping process produces two groupsof semiconductor: the negative charge conductor ( n-type ) and the positive

charge conductor ( p-type ).

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N-type semiconductor

Doped by pentavalent impurities which has 5 valence electrons to produce n-

type semiconductors by contributing extra electrons. The addition such asantimony, arsenic or phosphorus contributes free electrons, greatly increasingthe conductivity of the intrinsic semiconductor.

This allows four of the five electrons to bond with its neighbouring siliconatoms leaving one "free electron" to move about when an electrical voltage isapplied (electron flow).

P-type semiconductor

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Doped by trivalent impurities which has 3 valence electrons to produce p-type

semiconductors by producing a "HOLE". The addition such as boron,aluminium or gallium to an intrinsic semiconductor creates deficiencies ofvalence electrons, called "hole".

As there is a hole an adjoining free electron is attracted to it and will try tomove into the hole to fill it. However, the electron filling the hole leaves anotherhole behind it as it moves. This in turn attracts another electron which in turncreates another hole behind, and so forth giving the appearance that the holesare moving as a positive charge through the crystal structure

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Physics Form 5: Chapter 4 - P-N Junction of Semiconductor

A small quantity of electrons on the n-side of the junction are attracted by the"holes" in the p-side. They drift across the junction, and fill available holes.This causes a region across the junction to be depleted in carriers of current(that is, electrons and "holes"). This region is called the DEPLETION LAYER ,because it has been depleted in majority carriers. The depletion zone is a fewmicrometers thick, and, since it has no majority carriers, acts as an insulatingbarrier.

It is important to realise that when electrons moves from the n-side of the junction to the p-side, the n-side becomes positively charged (since neutralatoms have lost electrons), while the p-side of the junction now becomesnegatively charged (since neutral atoms have now acquired negatively

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charged electrons). A potential difference now exists across the junction. Thispotential difference is about 0.6 V for silicon, and about 0.2 V for germanium.This is called the BARRIER POTENTIAL .

Physics Form 5: Chapter 4 - How Transistor Works

The design of a transistor allows it to function as an amplifier or a switch . This

is accomplished by using a small amount of electricity to control a gate on amuch larger supply of electricity, much like turning a valve to control a supplyof water.Transistors are composed of three parts – a base, a collector,and an emitter.

Base = gate controller device for the larger electrical supply.Collector = larger electrical supply.Emitter = outlet for electrical supply.

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By sending varying levels of current from the base, the amount of currentflowing through the gate from the collector may be regulated. In this way, avery small amount of current may be used to control a large amount of current ,as in an amplifier. The same process is used to create the binary code for thedigital processors but in this case a voltage threshold of five volts is needed toopen the collector gate. In this way, the transistor is being used as a switchwith a binary function: five volts – ON, less than five volts – OFF.

We provide a reservoir of water for "C" (the "power supply voltage") but it can't

move because there's a big black plunger thing in the way which is blocking

the outlet to "E". The reservoir of water is called the "supply voltage". If we increase the amount of water sufficiently, it will burst our transistor justthe same as if we increase the voltage to a real transistor. We don't want to dothis, so we keep that "supply voltage" at a safe level.

If we pour water current into "B" this current flows along the "Base" pipe andpushes that black plunger thing upwards, allowing quite a lot of water to flowfrom "C" to "E". Some of the water from "B" also joins it and flows away.

If we pour even more water into "B", the black plunger thing moves up furtherand a great torrent of water current flows from "C" to "E".

Physics Form 5: Chapter 4 - Transistor as an Amplifier

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An amplifier circuit

IB = base currentIC

= collector currentIE = emitter currentVBB = base voltageVCC = collector voltage

The function of resistantR B is to control and limit the base current.

How transistors function as an amplifier: The forward-bias from base to emitter narrows the base-emitter,BE depletion

layer. The reverse-bias from base to collector widens the base-

collector, BC depletion layer. The free electrons from emitter diffuse easily through the forward-

biased BE junction into the p-type region. The base region is lightly doped and very thin, so it has a limited number of

holes. Therefore, only a small percentage of the all electrons flowingthrough BE junction can combine with the available holes in the base region. Most of the electrons do not combine with holes but diffuse intoBC depletion

layer. Once here, these electrons are pulled through the reverse-biasedBC junction

by the electric field set up by the force of attraction between the positive andnegative ions. Electrons now move through the collector region and into the positive terminal

of the collector voltage source. This forms collector current which is larger than the base current.

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MONDAY, AUGUST 22, 2011

Physics Form 5: Chapter 5 - Radioactive DecayRadioactive decay is the breaking up of unstable nuclei into more stable nuclei withthe emission of radioactive rays.

A) Alpha decay

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The reason alpha decay occurs is because the nucleus has too many protons whichcause excessive repulsion. In an attempt to reduce the repulsion, a Helium nucleusis emitted. The way it works is that the Helium nuclei are in constant collision withthe walls of the nucleus and because of its energy and mass, there exists a nonzeroprobability of transmission. That is, an alpha particle (Helium nucleus) will tunnel outof the nucleus

B) Beta decay

Beta decay occurs when the neutron to proton ratio is too great in the nucleus andcauses instability. In basic beta decay, a neutron is turned into a proton and anelectron. The electron is then emitted

C) Gamma decay

Gamma decay occurs because the nucleus is at too high an energy. The nucleusfalls down to a lower energy state and, in the process, emits a high energy photonknown as a gamma particle.

Physics Form 5: Chapter 5 - Application of Radioactive (Carbon-14 Dating)C-14 is another radioactive isotope that decays to C-12. This isotope is found in allliving organisms. Once an organism dies, the C-14 begins to decay. The half-life ofC-14, however, is only 5,730 years. Because of its short half-life, the number of C-14isotopes in a sample is negligible after about 50,000 years, making it impossible touse for dating older samples. C-14 is used often in dating artifacts from humans.

(Real mummy from Ramesses II)How old is he ..............?

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For determining age of fossils older than 60,000 years one uses a potassium-argondating technique. Potassium dating has a half life of 1.3 billion years, thus allowingthe age of rocks several billions years old to be determined. A more accurate "argon-argon" dating technique (determining the ratio between argon-39 and argon-40) hasalso been developed.Physics Form Five: Chapter 5 - Nuclear Fusion

Fusion is what happens when two atomic nuclei are forced together by highpressure and high temperature ... high enough to overcome the strong repulsiveforces of the respective protons in the nuclei. When the nuclei fuse, they form a newelement, and release excess energy in the form of a fast-moving neutron. The

energy is 'extra' because the mass of the newly formed nucleus is lessthan the sumof the masses of the original two nuclei; the extra mass is converted to energyaccording to Einstein's equation E=mc 2 . This energy can be used to do useful work!

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Deuterium can be easily extracted from seawater, where 1 in 6500 hydrogen atomsis deuterium. Tritium can be bred from lithium, which is abundant in the earth's crust.

In the fusion reaction a deuterium and tritium atom combine together, or fuse, toform an atom of helium and an energetic neutron.

Fusion is like lighting a match to a bucket of gasoline. You need that input energy(the match), but what you get as a result is far more powerful. Fusion fuel is veryenergy dense. A thimbleful of liquid heavy-hydrogen fuel could produce as muchenergy as 20 tons of coal. Or, more realistically, one pick-up truck full ofdeuterium would release the energy equivalent of approximately 2 million tons ofcoal (21,000 rail car loads), or 1.3 million tons of oil (10 million barrels), or 30 tons ofUranium Oxide (1 rail car load). Clearly, with seawater as our energy source, ourenergy problems would be over forever!

Physics Form 5: Chapter 5 - Nuclear Power Plant

Uranium-235 is used as a nuclear fuel at nuclear reactor. In nuclear fission, alot of heat will be produced. The moderators graphite stand are made of carbon blocks with small holes

used to slow down the motion of neutrons. Thus, the rate of nuclear fission can becontrolled.

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The boron and cadmium rods are used as control rods to absorb some of thesecondary neutrons. Carbon dioxide or water is used as a cooling agent in the nuclear reactor to

remove the heat of reaction to make steam for turbine generator. This producessteam as heat carrier. The lead and concrete shielding wall prevents the escape of radioactive rays

from the nuclear reactor.