Junior Cycle Junior Cycle Physics in ActionPhysics in Action

Edited and Reproduced by

Theresa 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 the environment

Examples:

3) An OUTPUT DEVICE – these are controlled by the processor

Examples:

2) A PROCESSOR – these decide what action is needed

Examples:

Logic gatesLogic gatesLogic gates are the basics behind any kind of processor. There are 3 that you need to know for GCSE:

NOT gate – “the output is NOT what the input is”

AND – “the output is on if A AND B are both on”

OR – “the output is on if A OR B are on”

Input Output

0 1

1 0

Input A Input B Output

0 0 0

0 1 0

1 0 0

1 1 1

Input A Input B Output

0 0 0

0 1 1

1 0 1

1 1 1

Logic gate symbolsLogic gate symbols

NOT gate:

AND gate:

OR gate:

Some problems to solveSome problems to solve

• The pump on a central heating system is switched on at room temperature 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 a hot radiator falls during the day ONLY. Include a test switch to check the operation of the buzzer.

• Design a circuit for a gardener that will warn them of cold conditions 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 takes a much _____ current, e.g. a _________. To do this the circuit would need a RELAY switch, a device made of an _______ that can operate a switch. A relay switch is activated by the small current and the switch part is placed in the circuit needing a large current:

Symbol for relay:

Words – motor, larger, electromagnet, small

M

The Resistor Colour CodeThe Resistor Colour CodeWe would use this to determine the value (in ) of a resistor:

0.01

0.1 5%

0 0 1

1 1 10 1%

2 2 100 2%

3 3 1k

4 4 10k

5 5 100k

6 6 1M

7 7 10M

8 8

9 9

Significant figures

Multiplier

Tolerance (no

band = 20%)

E.g this resistor would have a value of 42 x 10 = 420 and a tolerance of 5%

Drawing electronic circuitsDrawing electronic circuits

12V

0V

VThis voltmeter will read 12V

VIN

0V

This bulb and resistor are in parallel

Drawing electronic circuitsDrawing electronic circuits1) Two resistors in series

4) An ammeter measuring the current through a resistor

3) A voltmeter measuring the voltage across two bulbs in series

2) Two resistors in series with one bulb in parallel

VIN

0V

VIN

0V

VIN

0V

V

VIN

0V

A

Potential DividersPotential Dividers

0V

VIN

VOUT

0V

R1

R2

(R1 + R2)

VIN x(R2)VOUT

The Potential Divider equation:

Some example questionsSome example questions

0V

12V

VOUT

0V

100

100

0V

1.5V

VOUT

0V

50

45

0V

50V

VOUT

0V

10

75

0V

3V

VOUT

0V

75

25

Practical applicationsPractical applications

0V

Vin

VOUT

Here’s a potential divider that is used to control light-activated switches…

When the light intensity on the LDR decreases its resistance will ________. This causes VOUT to _______ so the processor and output will probably turn _____. The variable resistor can be adjusted to change the ________ of the whole device.

Words – decrease, sensitivity, increase, off

TransistorsTransistors

A transistor acts like a switch:

Base

Collector

Emitter

When a SMALL current flows through the base-emitter part of the transistor a different current is switched on through the collector-emitter part.

A light dependent switchA light dependent switch

6V

0V

Power supply

Output device

A light dependent switchA light dependent switch1) When the light on the LDR decreases its resistance _________,

which will decrease the ________ across the variable resistor

2) 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 resistor

3) The resistor limits the amount of current flowing into the transistor, to avoid __________ it

4) When the transistor detects the current at its _____ it will “switch __” the collector-emitter current

5) A small current will then flow through the _______

6) The relay will then switch on a _____ current in the output circuit

7) The “reversed biased” diode is also placed in the circuit to act as a “_______” to prevent current flowing back into the transistor when the relay is switched _____Words – base, buffer, on, increases,

damaging, relay, off, larger, voltage, drop, NOT

A light dependent switchA light dependent switch

6V

0V

We could modify this circuit (if we wanted to…)

2) Adjust this resistor to vary the sensitivity

1) Swap these two around and the output will now switch on when it becomes LIGHT, not when 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 voltage between them increases until it reaches the supply voltage.

Charging and discharging a Charging and discharging a capacitorcapacitor

P.d. across capacitor

Time

P.d.

Time

P.d.

Time Time

Increase resistance or capacitance

Increase resistance or capacitance

Time delay circuitsTime delay circuits

6V

0V

Power supply

Output device

R

Time delay circuitsTime delay circuits

“1”

6V

0V

Power supply

Output device

R

Time delay circuitsTime delay circuits1) When the switch is closed the capacitor is being short

circuited so no charge builds up on it

2) This means that the input to the NOT gate is __, so the output is 1 and the output device is ___

3) When the switch is released the capacitor starts to ________ up

4) When the voltage across the capacitor reaches a certain level the input to the NOT gate becomes __ so its output is 0

5) This means that the output device is now switched ___

6) To INCREASE the amount of time taken to switch the device off you could:

1) Increase the _________ of the capacitor

2) _________ the resistance of the resistor R

Words – charge, 1, capacitance, increase, 0, off, on

Electronic systemsElectronic systemsSystem Advantages Disadvantages

CCTV

Internet

Mobile Phones

LensesLensesLenses use the idea of refraction:

When light enters a MORE DENSE medium it slows down…

A prism uses this idea to split light. This happens because purple light is refracted more than red light

Another example:Another example:

The lens in the eye is used to focus what we see:

Converging and diverging Converging and diverging lenseslenses

CONVERGING (Convex)

Thickest at the centre

DIVERGING (Concave)

Thinnest at the centre

Ray diagramsRay diagramsThe rays of light are refracted INWARDS and meet at the focus, F.

The image formed is REAL – in other words, it can be seen on a screen

The rays of light are refracted OUTWARDS.

A VIRTUAL image is formed – in other words, the image doesn’t actually exist

F

F

Using lenses to correct Using lenses to correct visionvision

Short Long

Ray diagramsRay diagramsTo draw ray diagrams follow these two rules:

1) Draw a ray from the TOP of the object PARALLEL to the axis and then going through F:

2) Draw a ray from the TOP of the object going through the CENTRE of the lens (which will be undeviated)

F

This image is REAL, UPSIDE DOWN and SMALLER than the object

Practical uses of lensesPractical uses of lensesCameras use the lens arrangement where the object is beyond 2F – this is why they can’t be used at very short range.

Magnifying glasses use the arrangement where the object is between F and the lens – this is why they don’t work when you move them away from the object.