25. Explain the necessary modification for the structure of dentist chair for children that are suitable and save for the adult.

Suggestion ExplanationIncrease the cross-sectional area of big piston and decrease the cross-sectional area of small piston

To increase the output force acting on big piston / to lift havier adult / to increase force multiplier of system

The wall of pipe is made up of strong alloy to hold the fluid

To withstand the strong pressure that might cause cracking in the channel

Change the less control into electric touch control

To lift or lowered the chair to the desire weight more easily and safety

The surface area of the seat enlarged

To support the people with the large bodies

Use non-corrosive oil in jack So that the wall of the pipe will not be controlled and cause leakage

26. Explain the build and design of hot air ballon wich can fly higher altitude faster and suggest some safety aspect.

Suggestion ExplanationLarge ballon Produce bigger buoyant / upthrust force,

increase the volume of air displacementMany hot air burner Heat up the gas inside fasterSynthetic nylon ballon Air proof, light weight and strong materialGas temperature is high Reduce the density of air in ballonTotal of mass is low Ballon move upward fasterRattan basket Longer the time impact, reduce the impulsive

force to passanger when landingFly on early morning or late afternoon

The temperature outside the ballon is cooler compare to the inside of ballon, so the ballon will rise higher

27. Explain the basic structure of small submarine that can be use for underwater exploration.

Suggestion ExplanationStrong material Does not break easilyAerodynamic shape Reduce water resistanceThick wall Water pressure increase with depthHigh density materials Increase mass / can submerge easilyBallast tank To increase or reduce weightSonar transmitter and receiver

To estimate and depth

28.Suggest the design of submarine which can submerge and float in the sea.

Suggestion ExplanationBallast tank are partially filled with water

The submarine will partially float

Aerodynamic // streamline body

To reduce water resistance

Use hard and stiff materials for body

To overcome the pressure of water in the sea

Attach periscope To view surrounding area when submarine floatUse nuclear power sources to generate power

Cheap and lasting power

29.Explain the characteristic of material to be use for making the sole of jungle trekking shoes.

Suggestion ExplanationRubber sole Good impact absorberLow density Light weightMany stud Give extra gripLow expansion effect Not loose easilyExcellent ability of stretch Comfortable to feet, foot can move unstressed

30.Using physics concept, explain necessary deep sea diving suit and other accessory to carry.

Suggestion ExplanationChoose strong helmet with thick metal and glass to cover head

To withstand high pressure of water and protect the head

Use thick glass in front of diver face

Enable the diver to see surrounding and at the same time able to withstand the pressureof water

Use water proof suit and able to withstand pressure

Due to depth, the pressure under water is very high

Bring along gas containing mixture of oxygen

To provide oxygen to diver for breath

Use very heavy suit The diver enable to stand on the floor of ocean and able to fight buoyancy of water

31.Modified the passanger airplane to cargo airplane that needs to carry more laod, less use of fuel, effenciency and safety to travel.

Suggestion ExplanationIncrease the size of the body

To increase the space

Increase the length of the wing

To increase the upthrust

Increase the thickness of the body

To stand higher pressure difference

Use a more powerful engine

To overcome bigger inertia and do more work per unit time

Increase the number of tyres

To support higher mass or pressure while landing

Protective bar between the cabin and the pilot

To prevent moving object to knock at the pilot while landing

Pilot has ejected seat during emergency

To save the pilot if plane crash happened

32.Design Vacuum Cleaner

Suggestion ExplanationLarge fan driven Inrease the spped and amaunt of airflowsPowerfull of lectric motor Inrease the spped and amaunt of airflowsNarrower inlet opening Inrease the velocity/decrease air pressureUsing a very large filter to block dust particles while allowing air moleculs to pass through

To have a lots of surface area and many pores for air to flow through

Larger spaced for depositing and collecting the dust particles

Ensure that the air flows through the filter is not block by too many dust particles

33.Design paint sprayer

Suggestion ExplanationLarge size of air vessel Compress more air/can exert large pressureRubber material for the vessel More elastic/easier to squeezeNarrow shape of the tube Air can move with high speedFibre glass material for the rod Stronger and last longerSize of nozzle is narrow at the end

The paint can be sprayed evenly

34.Design hidraulic jack

Suggestion ExplanationBigger crossectional area of slave piston(big piston)

Produced higher force

Small crossectional area of master piston(small piston)

Less forced is needed/produced bigger pressurre

Longer handle Less forced is needed to press small piston(master piston)

Low density of a body LighterOil for liquid Non-compressableRelease valve between small and main reservoir(reset)

Liquid can flows into small reservoir easily when push the reset button.

35.Design hydrometer

Suggestion ExplanationBulb with lead shot at the lower section

To submerge the hydrometer and not overturn

Cylinder with bigger diameter at the bottom

not overturn/increase stability

Cylinder with smaller diameter at the upper section

A small reading scale can be incorporated/inrease the sensitivity

Smaller scale inrease the sensitivityFilled with air Inrease the beyoncy forceGlass wall Not corrode easily

CHAPTER 4

36.Most suitable design of thermometer to use in Antarctica

Suggestion ExplanationUse alcohol as liquid in glass thermometer

Freezing point of alcohol is -115oC .So , it will not freeze at low temperature

Use thin wall of bulb So it will sensitive to the change of heatUse small diameter of capillary tube

Alcohol can expand at high rate for the small change in temperature

Use thick glass wall The loss of heat to surrounding is smallUse round glass stem Can act as magnifying glass , so the alcohol level can be

seen clearer

37.Most suitable design of clinical thermometer

Suggestion ExplanationUse mercury Easy to read because it colour and opaqueThe scale range from 35oC to 42oC

To measure human body heat

Small diameter of capillary tube// extra fine bore tube

Mercury can expand at high rate for a small change in temperature

Use thin glass wall of bulb

Sensitive to change of temperature

Use round glass stem and wall

Can act as ,magnifying glass. So, mercury can be seen clearly

38.Explain the design and the characteristics of the cooking pan

Suggestion ExplanationBase is made of a copper Copper has a lower heat capacity it become hot very

quicklyHigh density of base Heavier base make the pot stable and not topple over

easilyBody is made of aluminium

Low specific heat capacity becomes hot very quickly but it low density make it overall weight of weight lighter

Handle is made of wood or plastic

High specific heat capacity so the handle do not become hot . Safe

Choose low density material for handle

Does not add much to the total weight of pot

Transparent pot cover Able to cooker to see the food. Food cover will trap the heat

39.Suggest and explian the design of water heater to boil a large quantity of water faster, efficient and safely

Suggestion ExplanationUse tungsten High melting point,high heat energyCoiled Longer wire,increase the resistanceHigh melting point Not easy to melt at high temperatureLower rate of rusting Does not get rust easilyUse thermostat When temperatures reach 100 Celsius, the water heater

will automatically turn off

40.Determine the modification to be made for container,so the cut fruit will keep cool, remain fresh and easily seen by customers.

Suggestion ExplanationUse container with high specific heat capacity

Able to slow down the loss of heat from the container

Place small ice packet below the bottom of the cut friuts

The cut fruits is chill and juicy, ice able to absorb a large amount of latent heat when melt

Add salt to the packet of ice Foreign matter will increase the freezing point of ice, so this will slow down the ice from melting

White wall colour of container Can avoid absorbtion of heat from the surrounding

The container has double wall Avoid heat from surrounding transferred easily to container. The inside container remains cool

Transparent wall of container in front of customer

The customer can see and choose the cut fruits easily

41.Investigate the most suitable liquid that can be use as coolant for car engine using physics concept.

Suggestion ExplanationLow freezing point liquid Will not freeze easily during winter weatherHigh boiling point liquid Do not easily boil when absorbing heat from the

engineHigh specific heat capacity liquid

Can transfer large contain of heat with a small rise in temperature. Able to cool up the engine

Low ability to react with metal The metal part of the engine will not corrode easily

42.Most suitable thermometer for laboratory to measure the temperature of ice and boiling point of water

Suggestion ExplanationSize of the bulb is small Does not need a lot of heat to heat up the mercury

to expandUse thin wall of bulb So it is sensitive to change of heatUse mercury Freeezing point of the mercury is -39 degree celsius

and boling point 357 degree celsius . Able to has a range from -10 to 110 degree Celsius. Mercury can expand a high rate for small change of temperature

Use thin wall capillary Able quick heat transfer from the surrounding to the mercury. So, the thermemeter is more sensitive

Has minimum size scale with small division

Making thermometer a sensitive instrument

43.Modified and explain the design of an efficient solar water-heating system on the roof.

Suggestion ExplanationPipe embedded in plate must be long

Longer pipe will has greater surface area which can absorb heat faster

Use metal pipe as pipe inside the plate

Metal is good heat conductor , so heat will easily transmit to water

Use insulator behind the absorber panel

Insulator will prevent the heat loss

Use black absorber panel Black is good heat absorberCover the top of the panel with glass

Heat will trap inside due to green house effect

Put the tank at higher level To give higher pressure

44.Explain the build of solar cooker oven that been use in science month competition at your school to boil 500ml water in short time.

Suggestion ExplanationBuild the solar cooker with shiny// silver colour reflectorinside

The light will reflect to the cooker and heat up the water

Use metal cooker Good conductorPaint the outside part of the solar cooker and the cooker ( contain water ) with black colour

To absorb

Wrap the cooker with plastic or glass

Avoid heat from release to sorrounding

To trap heat, the temperataure will increase

To absorb heat, the water boil faster

45.Suggest the design of heating system in the house and characteristics of heating agent. The house use central heating system with boiler, radiator and pipelines.

Suggestion ExplanationUse strong material Not easily breakUse metal pipe with good heat conductor

Increase the rate of heat transfer

Increase length of cooling coil Can transfer the heat faster to surroundingUse greater boiling point liquid Liquid not easily change into vapourLow rate of rusting material Long lasting, not easily rustThe bigger size of radiator fan Can blow and cool down larger areaPipe in coil structure is used Increase the time of floe and increase the quantity of

haet transferred.

46. Suggest the characteristic of material to build food container which can keep the food warm.

Suggestion ExplanationFood container should made of low density material

Lighter , the container able to be move from one place to another.

Melting point of container should be high

To prevent the container from melting up when hot food is store inside

Specific heat capacity should be high

So the container will not get hot easily. Safe to touch and handle.

Thermal conductivity is low.i Good heat insulator , to ensure the heat not loss and the food remain hot.

Double wall To prevent hest loss.

47.Explain the characteristic and design of thermos flasks to maintain hot water.

Suggestion ExplanationUse hollow plastic stopper Able to trap air as air is poor heat conductor.so,less heat

loss through stopper.Vacuum space Prevent heat loss through conduction or convectionHas double wall Has vacuum in between heat not easier pass through

the wall of thermos.Double walled tube coated with shiny paint

Shiny surface reflect heat from the wall of thermos flasks back to water.so the water remain hot.

Double walled made of glass Glass is bad conductor.it will reduce heat loss.

48.Explain how the design of radiator of the car and characteristic of cooling agent which can absorb heat at short time,

Suggestion ExplanationIncrease the length/area of cooling coil

Can transfer the heat faster to the surrounding

Increase the number of fin blades

Can cool down faster

Use larger fan Can cool down larger areaUse cooling agent liquid with greater boiling point

It wont boild easily in high temperature

Use cooling agent liquid with higher specific heat capacity

Able to absorb large amount of heat

CHAPTER 5

49.Determine and explain in the build of magnifying glass to be use for enlarging the image of stamp

Suggestion ExplanationChoose convex lens The image will magnifyExcellent clarity of lens The image is clearerSmall focal length Able to focus nearerMedium diameter of lens Able to be hold by hand to identify the stampsThe object is place less distance than focal length

The image form is magnify, virtual and upright

50.Explain the suitability of the mirror that be use in shop to watch over the customer

Suggestion ExplanationUse convex mirror Wider field of viewGreater reflectivity of material Clearer image Choose a bigger size of mirror Enable wider view and sharper imagePlace the mirror at the corner of shop ceiling

Easier to look at and wont disturb the customer pathway

Low density Lighter to hang up

51.Design fibre optic

Suggestion ExplanationUse refractive index of outer layer is less than the refractive index of inner layer

So that total internal reflection can happen in the fiber optic.

Use high flexibility material so that it can be bend easilyUse strong material do not break easilyUse thin material Lighter // can be use in small areaLow density material Lighter

52.Determine and explain the build of microscope using lens P and Q with focal length of 15 cm and 5 cm respectively. Suggest modification that need to be done to get brighter ang bigger image.

Suggestion ExplainationP as eye piece and Q as objective lens

Focal length of P is longer than Q

Fo < u fo + fe To produce bigger image from the eyepiece // to

increase the magnificationStore in a cool and dry place To avoid formation fungus at the lensesUse more powerful// shorter focal length lenses

To produce bigger image

Use a lamp near the object// use bigger diameter of objective lens

To produce brighter image

53.Explain the suitable characteristic of the mirror to be use as outdoor safety mirror at the corner of the road

Suggestion ExplanationUse convex mirror Wider field of viewExcellent weather resistance Able to withstand bad weatherExcellent impact resistance of material

Save cost, everlasting

Bigger size mirror To enable a wider view and sharper imageGreater reflectivity of material Clearer image even in bad weatherPlace at the sharp road corner , at bending road

To minimize from accident occur, to enable motorist see the oncoming traffic

Small roof Protect from rain drop for better image

54.Detemine and explain the build of Astro disc using appropriate physics concepts.

Suggestion ExplanationChoose convex curve parabolic The signals come can be focus at one pointAll signal are focus on focal point Better receptionSmooth surface of disc Better reflectionLocate the disc at high and facing towards satellite

No obstacle, better signal

Clean surface of disc, no water drop or dirt

Better reflection, almost 100% reception receive by feed horn

55.Modified the slide projector that need to be place in school hall and can be seen by many student with clearer image.

Suggestion ExplainationUse higher power bulb Higher intensity of light or more light producedThe filament of the bulb is at the focus point of the concave mirror

The light focuses at one point. // parallel ray can be obtained after reflection by concave mirror

More curvature More light to be reflected (upward) // less light toward other direction other than upward

Lens between f and 2f To produce real ang enlarge or bigger imagesIncrease the distance or further away the screen

Larger image produced

Electric fan operates during and after the lamp is switches on

Cooling system to stabilized the temperature (heat energy produced by filament bulb) to increase the projector lifetime

Use condenser mirror To concentrate more light to the slideUse a concave mirror instead of plane mirror

Focus the light directly to the lens // increase the intensity og light

Place the filament at centre of curvature of the converging mirror // use high powered lens

Light goes directly from the lamp and reflect back on the same path // increase the intensity of light toward the transparency // to get brighter image

Use heat filter To absorb excess heat to the transparency

56.Determine and explain the build of telescope using lens J and K with lens K is thicker than lens J which produce bigger and clearer image.

Suggestion Expalanation C hoose lens K as eyepiece

lens Lens K is thicker than lens J

Light ray is refracted more in lens K than lens J, focal length of lens K is shorter than lens J

Therefore the thickerthe lens, the greater the refraction of light and with that the shorter the focal length of a lens will be

Choose lens J as objective lensUse bigger diameter lens as objective lens

Characteristics of objective lens for telescope is Has larger surface area which allow more

light enter Has a longer focal length

Use low power convex lens as the objective lens

Magnification of telescope =f0/feLow power lens has a longer focal length ,fo higher, magnification higher

Use high power convex lens as the eye lens

High power lens has a shorter focal length,fe higher, magnnification higher

Use bigger diameter of objective lens

More light permitted to enter the telescope and a clearer image is seen