EP Revision

Question 1

Answer 1

Lamp or bulb

Question 2

Answer 2

Push to make switch

The current can flow only when the switch is pressed.

The button part is often (but not always) red

Question 3

Answer 3

NOT gate

Question 4

Answer 4

Double Pole Double Throw

Poles are the number of switches inside the main switch. Throws are the number of outputs the switch has.

You can tell the number of these by looking at the number of pins or legs the switch has.

The toggle switch below is a double pole double throw (DPST) since it has 6 connections..

These are the most common switches you will see because by using some or all of the connections you can make the switch act like any of the other types.

Question 5

Answer 5

AND gate

Question 6

Answer 6

Voltmeter

Question 7

Answer 7

Ammeter

Question 8

HIGH IMPACT POLYSTYRENE

Answer 8

High Impact Polystyrene Sheet (HIPS) is available in various thicknesses and colours (mostly opaque).

It is waterproof, self coloured (no need to paint), does not conduct electricity and can be heated until it is soft and then have it’s shape changed (called thermoplastic or thermoforming)

Commonly used with a mould in vacuum forming and can be glued (with solvent cement) or even welded together (industrial process really)

Question 9

Answer 9

Latching switches

All of these stay in one position until deliberately changed. They do not spring back when let go. They can all use this symbol.

Question 10

Answer 10

Micro switch

These switches are different because they are not operated by a persons finger, but usually part of a machine or piece of equipment.

They can have buttons, levers or rollers and are used to detect when a fridge door is closed, a machine has a guard in place, or when part of a machine has reached the end of it’s movement.

Question 11

Answer 11

Light emitting diode (LED)

Question 12

Answer 12

Motor

Question 13

ALUMINIUM

Answer 13

Lightweight, non-rusting, good conductor of heat and electricity, expensive but can be melted down and reused quite straightforwardly (with a big factory and furnaces… - NOT “easy”)

Can be machined (using computer controlled machines - CNC), cast (heated to a liquid and poured into moulds) or, in sheet form, bent into boxes

Pure aluminium is quite soft for a metal and so is often mixed or alloyed with other metals to improve it’s properties.

Question 14

Answer 14

Single Pole Single Throw

Poles are the number of switches inside the main switch. Throws are the number of outputs the switch has.

You can tell the number of these by looking at the number of pins or legs the switch has.

The rocker switch below is a single pole single throw (SPST) since it only has 2 connections.

You can find more information here(right click and ‘open in new tab’ to not lose your progress here)

Question 15

Answer 15

Exclusive OR gate (XOR or EOR)

Question 16

Answer 16

Electrolytic or polarised capacitor

Question 17

Answer 17

Buzzer

Question 18

Answer 18

Toggle switches

Theses are often (but not always) used as ON/OFF switches and are sometimes marked with these labels

They usually mount through a hole drilled into the material they are used in and fastened with a nut on the front.

They can be SPDT or DPDT (and sometimes other forms as well)

Question 19

Answer 19

NOR gate

Question 20

Answer 20

Loudspeaker

Question 21

ACRYLIC

Answer 21

Acrylic (also known as Perspex) is a ‘thermoplastic’ – it will go soft when you heat it and you can change it’s shape. It can be bent on a line bender or injection moulded. It also laser cuts well.

It is waterproof, self coloured (no need to paint), does not conduct electricity and is available in different thicknesses as well as lots of opaque and translucent colours and also clear.

It is quite strong (for a plastic) and is hard but may shatter if a large force is applied. It can be used for cases for circuits or as covers for displays where it can protect them

Question 22

Answer 22

Thyristor

Question 23

Answer 23

Diode

Question 24

Answer 24

Resistor

Question 25

Answer 25

Push to break switch ## Footnote The current only flows when the switch is not pressed - pressing the switch stops the current. If it is a push switch the button is often (but not always) black

Question 26

Answer 26

OR gate

Question 27

Answer 27

Relay

Question 28

**PINE**

Answer 28

Softwood (needles rather than leaves), fast growing (about 35 years), needs protecting (paint or varnish), OK rather than beautiful, easy to cut and glue into boxes, sustainable (trees are cut down and then replaced and grown in large plantations around the world - Scandinavia is a big, close by, producer), narrow trunks and very thin (useless) branches mean methods must be used to join them together to make bigger boards (like in IKEA furniture)

Question 29

**BRASS**

Answer 29

Alloy (mixture) of copper and zinc. Strong, rust proof, machines and recycles well, conducts heat and electricity well, Used a lot before stainless steel became common (door knobs etc) but used a lot today for electrical connections inside plugs, battery compartments etc

Question 30

Answer 30

Single Pole Double Throw ## Footnote Poles are the number of switches inside the main switch. Throws are the number of outputs the switch has. You can tell the number of these by looking at the number of pins or legs the switch has. The slide switch below is a single pole double throw (SPDT) since it has 3 connections.

Question 31

Answer 31

Momentary switches ## Footnote All of these allow current to flow when pressed but it stops as soon as they are released - they do not 'stay on' They can all use the 'push to make'symbol

Question 32

Answer 32

Reed switch ## Footnote These are momentary switches activated by a magnet . If there is a magnet close by the switch conducts, but if there is no magnet then the switch stops conducting. They are common switches and are frequently used in alarm circuits where they might be packaged in plastic to protect the glass tube

Question 33

**COPPER**

Answer 33

Very good conductor of electricity (and heat) and is ductile - it can be stretched out into long thin wires without breaking. Most common use for us is in wires and cables (covered with plastic to stop it touching other wires and to help identify a particular wire) Also used for the tracks on PCBs. Doesn't rust and recycles well but is expensive

Question 34

Answer 34

Light dependent resistor (LDR)

Question 35

Answer 35

Variable resistor

Question 36

Answer 36

Battery

Question 37

**MDF**

Answer 37

Medium Density Fibreboard (softwood trees ground into fine dust, mixed with glue and them rolled into very wide, thin sheets of different thicknesses). Large sheets mean large objects can be made easily. Consistent quality, thickness, weight etc. Cuts and glues well Sustainable as all of tree is used and new trees can be planted that can be harvested after 25 years (less than full trees) Needs covering to protect and improve appearance - paint or thin covering of another wood (veneer) or a laminate such as formica used in kitchen tops or doors

Question 38

Answer 38

Capacitor

Question 39

Answer 39

Transistor

Question 40

Answer 40

NAND gate

Question 41

**MILD STEEL**

Answer 41

Strong and one of the cheaper metals Magnetic, conducts electricity (but see below) and heat and can be delivered in flat, round or pre-shaped pieces. It is heavy and rusts in the presence of oxygen, which gets worse in wet or damp conditions. It will need to be protected, commonly by painting. Rusting can prevent an electrical connection from being made (use copper or brass if this is likely)

Question 42

Answer 42

Switch

Question 43

Answer 43

Thermistor

Question 44

**LIGHT DEPENDENT RESISTOR**

Answer 44

...or LDR A resistor whose value depends on how light or dark it is In the dark it is a big resistor

Question 45

**THERMISTOR**

Answer 45

A resistor whose value depends on how hot or cold it is. It is a big resistor when it is cold.

Question 46

**MOISTURE SENSOR**

Answer 46

These can be thought of as a type of resistor. When they are dry they have a very big resistance but when they are wet it drops a little (but is still quite big!) There are two main types. One type has two 'probes' and is often put into plant pots as part of a system to water them - when the soil is dry they have a very big resistance and when the soil is moist the resistance is lower. The other sort has two PCB tracks that interlock but don't touch. When it is dry it has a very high resistance but of a drop of water lands on it and joins the tracks the resistance gets lower. These are often used as rain sensors. Both types can be made in school and there is no symbol.

Question 47

**PIEZO ELECTRIC SENSOR**

Answer 47

Piezo electric materials produce a **_very_** small voltage when a force is exerted on them. They are used on phones to detect when the 'home' or 'back' buttons are pressed but can also be used in alarms to detect if a door is being hit or pushed by a burglar.

Question 48

**BIOSENSORS**

Answer 48

Biosensors are electronic devices that have an electrical output that changes due to a biological effect. This is a new and developing field but examples include:- Sensors that react to the biological releases from micro-organisms that occur when food deteriorates so we can build packaging that tells us when the food is dangerous to eat. Sensors attached to the skin or built into clothing that can monitor changes that occur during exercise to help plan more effective training either for elite athletes or those recovering from surgery