Junior cycle science physics in action. By Theresa Lowry-Lehnen. Science Teacher.
Junior CycleJunior CyclePhysics in ActionPhysics in ActionEdited and Reproduced byTheresa Lowry-LehnenRGN, BSc (Hon’s) Specialist Clinical Practitioner (Nursing), Dip Counselling, Dip Adv Psychotherapy, BSc(Hon’s) Clinical Science, PGCE (QTS) , H. Dip. Ed, MEd, Emotional Intelligence (Level 9) MHS Accredited
Electronic systemsElectronic systemsElectronic systems are made up of 3 parts:1) An INPUT SENSOR – these detect changes in theenvironmentExamples:3) An OUTPUT DEVICE – these are controlled by theprocessorExamples:2) A PROCESSOR – these decide what action is neededExamples:
Logic gatesLogic gatesLogic gates are the basicsbehind any kind ofprocessor. There are 3that you need to know forGCSE:NOT gate – “the output isNOT what the input is”AND – “the output is on if AAND B are both on”OR – “the output is on if AOR B are on”Input Output0 11 0Input A Input B Output0 0 00 1 01 0 01 1 1Input A Input B Output0 0 00 1 11 0 11 1 1
Some problems to solveSome problems to solve• The pump on a central heating system is switched on at roomtemperature if the system is switched on (with the slide switch).When the temperature rises the pump needs to be switched off.• Design a circuit that will sound a buzzer if the temperature of ahot radiator falls during the day ONLY. Include a test switch tocheck the operation of the buzzer.• Design a circuit for a gardener that will warn them of coldconditions at night. The alarm should be able to be switched off.
RelaysRelaysCircuits such as those containing logic gates only take very ______currents. These circuits may be needed to operate a device that takesa much _____ current, e.g. a _________. To do this the circuit wouldneed a RELAY switch, a device made of an _______ that can operate aswitch. A relay switch is activated by the small current and the switchpart is placed in the circuit needing a large current:Symbolfor relay:Words – motor, larger,electromagnet, smallM
The Resistor Colour CodeThe Resistor Colour CodeWe would use this to determinethe value (in Ω) of a resistor:0.010.1 5%0 0 11 1 10 1%2 2 100 2%3 3 1k4 4 10k5 5 100k6 6 1M7 7 10M8 89 9Significant figuresMultiplierTolerance(no band =20%)E.g thisresistor wouldhave a value of42 x 10 = 420Ωand a toleranceof 5%
Drawing electronic circuitsDrawing electronic circuits1) Two resistors in series4) An ammeter measuring thecurrent through a resistor3) A voltmeter measuring thevoltage across two bulbs inseries2) Two resistors in series withone bulb in parallelVIN0VVIN0VVIN0VVVIN0VA
Some example questionsSome example questions0V12VVOUT0V100 Ω100 Ω0V1.5VVOUT0V50 Ω45 Ω0V50VVOUT0V10 Ω75 Ω0V3VVOUT0V75 Ω25 Ω
Practical applicationsPractical applications0VVinVOUTHere’s a potentialdivider that is used tocontrol light-activatedswitches…When the light intensity on the LDR decreases itsresistance will ________. This causes VOUT to _______so the processor and output will probably turn _____. Thevariable resistor can be adjusted to change the ________of the whole device.Words – decrease, sensitivity, increase, off
TransistorsTransistorsA transistor acts like a switch:BaseCollectorEmitterWhen a SMALL currentflows through the base-emitter part of thetransistor a differentcurrent is switched onthrough the collector-emitter part.
A light dependent switchA light dependent switch6V0VPower supplyOutputdevice
A light dependent switchA light dependent switch1) When the light on the LDR decreases its resistance _________,which will decrease the ________ across the variable resistor2) This will cause VOUT to ____. The____ gate will recognise this as a“0” and convert it into a “1”, i.e. a current will flow into the resistor3) The resistor limits the amount of current flowing into thetransistor, to avoid __________ it4) When the transistor detects the current at its _____ it will“switch __” the collector-emitter current5) A small current will then flow through the _______6) The relay will then switch on a _____ current in the output circuit7) The “reversed biased” diode is also placed in the circuit to act as a“_______” to prevent current flowing back into the transistorwhen the relay is switched _____Words – base, buffer, on, increases, damaging,relay, off, larger, voltage, drop, NOT
A light dependent switchA light dependent switch6V0VWe could modify this circuit (if we wanted to…)2) Adjust thisresistor to vary thesensitivity1) Swap these twoaround and theoutput will nowswitch on when itbecomes LIGHT, notwhen it becomes dark
The CapacitorThe CapacitorA capacitor is a device that can store charge (it has a“capacity”). It is basically made of two plates:…or…Charge builds up on these plates and the voltagebetween them increases until it reaches the supplyvoltage.
Charging and discharging a capacitorCharging and discharging a capacitorP.d. acrosscapacitorTimeP.d.TimeP.d.Time TimeIncreaseresistance orcapacitanceIncreaseresistance orcapacitance
Time delay circuitsTime delay circuits6V0VPower supplyOutputdeviceR
Time delay circuitsTime delay circuits“1”6V0VPower supplyOutputdeviceR
Time delay circuitsTime delay circuits1) When the switch is closed the capacitor is being short circuited sono charge builds up on it2) This means that the input to the NOT gate is __, so the output is1 and the output device is ___3) When the switch is released the capacitor starts to ________ up4) When the voltage across the capacitor reaches a certain level theinput to the NOT gate becomes __ so its output is 05) This means that the output device is now switched ___6) To INCREASE the amount of time taken to switch the device offyou could:1) Increase the _________ of the capacitor2) _________ the resistance of the resistor RWords – charge, 1, capacitance, increase, 0, off, on
LensesLensesLenses use the idea of refraction:When light enters aMORE DENSE mediumit slows down…A prism uses this ideato split light. Thishappens because purplelight is refracted morethan red light
Another example:Another example:The lens in the eye is used to focus what we see:
Converging and diverging lensesConverging and diverging lensesCONVERGING (Convex)Thickest at the centreDIVERGING (Concave)Thinnest at the centre
Ray diagramsRay diagramsThe rays of light arerefracted INWARDS andmeet at the focus, F.The image formed is REAL –in other words, it can beseen on a screenThe rays of light arerefracted OUTWARDS.A VIRTUAL image is formed– in other words, the imagedoesn’t actually existFF
Using lenses to correct visionUsing lenses to correct visionShort Long
Ray diagramsRay diagramsTo draw ray diagrams follow these two rules:1) Draw a ray from the TOP of the object PARALLEL tothe axis and then going through F:2) Draw a ray from the TOPof the object going throughthe CENTRE of the lens(which will be undeviated)FThis image isREAL, UPSIDEDOWN andSMALLER thanthe object
Practical uses of lensesPractical uses of lensesCameras use the lens arrangement where theobject is beyond 2F – this is why they can’t beused at very short range.Magnifying glasses use the arrangement wherethe object is between F and the lens – this iswhy they don’t work when you move them awayfrom the object.