Resource for Junior Cert

1. Junior CycleJunior Cycle
PhysicsPhysics
Physics inPhysics in
ActionAction
Edited and Reproduced by
Theresa Lowry-Lehnen
RGN, 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

2. Electronic systemsElectronic systems
Electronic 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:

3. Logic gatesLogic gates
Logic 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

4. Logic gate symbolsLogic gate symbols
NOT gate:
AND gate:
OR gate:

5. 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.

6. RelaysRelays
Circuits 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

7. The Resistor Colour CodeThe Resistor Colour Code
We would use this to determine
the value (in Ω) 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 = 420Ω
and a tolerance
of 5%

8. Drawing electronic circuitsDrawing electronic circuits
12V
0V
V
This voltmeter
will read 12V
VIN
0V
This bulb and
resistor are in
parallel

9. Drawing electronic circuitsDrawing electronic circuits
1) 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

10. Potential DividersPotential Dividers
0V
VIN
VOUT
0V
R1
R2
(R1 + R2)
VIN x
(R2)
VOUT
The Potential Divider equation:

11. Some example questionsSome example questions
0V
12V
VOUT
0V
100 Ω
100 Ω
0V
1.5V
VOUT
0V
50 Ω
45 Ω
0V
50V
VOUT
0V
10 Ω
75 Ω
0V
3V
VOUT
0V
75 Ω
25 Ω

12. 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

13. 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.

14. A light dependent switchA light dependent switch
6V
0V
Power supply
Output
device

15. A light dependent switchA light dependent switch
1) 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

16. 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

17. The CapacitorThe Capacitor
A 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.

18. Charging and discharging a capacitorCharging and discharging a capacitor
P.d. across
capacitor
Time
P.d.
Time
P.d.
Time Time
Increase
resistance or
capacitance
Increase
resistance or
capacitance

19. Time delay circuitsTime delay circuits
6V
0V
Power supply
Output
device
R

20. Time delay circuitsTime delay circuits
“1”
6V
0V
Power supply
Output
device
R

21. Time delay circuitsTime delay circuits
1) 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

22. Electronic systemsElectronic systems
System Advantages Disadvantages
CCTV
Internet
Mobile Phones

23. LensesLenses
Lenses 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

24. Another example:Another example:
The lens in the eye is used to focus what we see:

25. Converging and diverging lensesConverging and diverging lenses
CONVERGING (Convex)
Thickest at the centre
DIVERGING (Concave)
Thinnest at the centre

26. Ray diagramsRay diagrams
The 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

27. Using lenses to correct visionUsing lenses to correct vision
Short Long

28. Ray diagramsRay diagrams
To 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

30. Practical uses of lensesPractical uses of lenses
Cameras 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.