Physics in Action

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Physics in Action
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Electronic systems
Electronic systems are made up of 3 parts

• An INPUT SENSOR these detect changes in the
  environment
• Examples

2) A PROCESSOR these decide what action is
needed Examples
3) An OUTPUT DEVICE these are controlled by
the processor Examples
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Logic gates
NOT gate the output is NOT what the input is
Logic gates are the basics behind any kind of
processor. There are 3 that you need to know for
GCSE
AND the output is on if A AND B are both on
OR the output is on if A OR B are on
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Logic gate symbols
NOT gate
AND gate
OR gate
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Some 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.

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Relays
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
Words motor, larger, electromagnet, small
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The Resistor Colour Code
We would use this to determine the value (in ?)
of a resistor
E.g this resistor would have a value of 42 x 10
420? and a tolerance of 5
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Drawing electronic circuits
12V
0V
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Drawing electronic circuits
1) Two resistors in series
2) Two resistors in series with one bulb in
parallel
4) An ammeter measuring the current through a
resistor
3) A voltmeter measuring the voltage across two
bulbs in series
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Potential Dividers
VIN x
(R1 R2)
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Some example questions
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Practical applications
Heres 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
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Transistors
A transistor acts like a switch
Collector
When a SMALL current flows through the
base-emitter part of the transistor a different
current is switched on through the
collector-emitter part.
Base
Emitter
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A light dependent switch
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A light dependent switch

• When the light on the LDR decreases its
  resistance _________, which will decrease the
  ________ across the variable resistor
• 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
• The resistor limits the amount of current flowing
  into the transistor, to avoid __________ it
• When the transistor detects the current at its
  _____ it will switch __ the collector-emitter
  current
• A small current will then flow through the
  _______
• The relay will then switch on a _____ current in
  the output circuit
• 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
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A light dependent switch
We could modify this circuit (if we wanted to)
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The Capacitor
A capacitor is a device that can store charge (it
has a capacity). It is basically made of two
plates
Charge builds up on these plates and the voltage
between them increases until it reaches the
supply voltage.
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Charging and discharging a capacitor
P.d.
Time
P.d.
Time
Time
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Time delay circuits
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Time delay circuits
R
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Time delay circuits

• When the switch is closed the capacitor is being
  short circuited so no charge builds up on it
• This means that the input to the NOT gate is __,
  so the output is 1 and the output device is ___
• When the switch is released the capacitor starts
  to ________ up
• When the voltage across the capacitor reaches a
  certain level the input to the NOT gate becomes
  __ so its output is 0
• This means that the output device is now switched
  ___
• To INCREASE the amount of time taken to switch
  the device off you could
• Increase the _________ of the capacitor
• _________ the resistance of the resistor R

Words charge, 1, capacitance, increase, 0, off,
on
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Electronic systems
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Lenses
Lenses use the idea of refraction
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Another example
The lens in the eye is used to focus what we see
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Converging and diverging lenses
CONVERGING (Convex) Thickest at the centre
DIVERGING (Concave) Thinnest at the centre
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Ray 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
F
The rays of light are refracted OUTWARDS. A
VIRTUAL image is formed in other words, the
image doesnt actually exist
F
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Using lenses to correct vision
Short
Long
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Ray 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
F
2) Draw a ray from the TOP of the object going
through the CENTRE of the lens (which will be
undeviated)
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Practical uses of lenses