Physics in Action W Richards Worthing High School

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:

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: Input Output 1 Input A Input B Output 1 AND – “the output is on if A AND B are both on” Input A Input B Output 1 OR – “the output is on if A OR B are on”

Logic gate symbols NOT gate: AND gate: OR gate:

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.

The Relay

Words – motor, larger, electromagnet, small 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: M Symbol for relay: Words – motor, larger, electromagnet, small

The Resistor Colour Code We would use this to determine the value (in ) of a resistor: Significant figures 0.01 0.1 5% 1 10 1% 2 100 2% 3 1k 4 10k 5 100k 6 1M 7 10M 8 9 E.g this resistor would have a value of 42 x 10 = 420 and a tolerance of 5% Tolerance (no band = 20%) Multiplier

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

Drawing electronic circuits 1) Two resistors in series 2) Two resistors in series with one bulb in parallel VIN 0V VIN 0V 3) A voltmeter measuring the voltage across two bulbs in series 4) An ammeter measuring the current through a resistor VIN 0V V VIN 0V A

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

Some example questions 0V 12V VOUT 100  0V 50V VOUT 10  75  0V 3V VOUT 75  25  0V 1.5V VOUT 50  45 

Practical 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

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

A light dependent switch 6V 0V Power supply Output device

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

A light dependent switch We could modify this circuit (if we wanted to…) 1) Swap these two around and the output will now switch on when it becomes LIGHT, not when it becomes dark 6V 0V 2) Adjust this resistor to vary the sensitivity

The 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.

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

Time delay circuits 6V 0V Power supply Output device R

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

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

Electronic systems System Advantages Disadvantages CCTV Internet Mobile Phones

Lenses 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

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

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

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 doesn’t actually exist F

Using lenses to correct vision Short Long

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 This image is REAL, UPSIDE DOWN and SMALLER than the object 2) Draw a ray from the TOP of the object going through the CENTRE of the lens (which will be undeviated)

Practical 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.