P6 - Electricity For Gadgets Flashcards
1
Q
P6 - Electricity For Gadgets
What is current?
A
Flow of charge (electrons) round circuit. Only flows through a component if there is a voltage across that component. Measured in amps, A.
2
Q
P6 - Electricity For Gadgets
What is voltage?
A
It pushes the current around. It is measured in volts V.
3
Q
P6 - Electricity For Gadgets
What is resistance?
A
Anything in the circuit that reduces current and is measured in ohms.
4
Q
P6 - Electricity For Gadgets
What causes resistance?
A
Collisions in a conductor. Electrons flow through a conductor and collide with metal atoms causing resistance. Collisions cause atoms to vibrate and more they get in way. Increased collisions means increased resistance and temperature of conductor.
5
Q
P6 - Electricity For Gadgets
What is resistance like in longer wires?
A
More resistance, less current. Because longer wires have more atoms - electrons will collide.
6
Q
P6 - Electricity For Gadgets
What is a variable resistor?
A
(Or rheostat) is a resistor whose resistance can be changed. Great for controlling current.
7
Q
P6 - Electricity For Gadgets
What are variable resistors used for?
A
Controlling speed of motors and brightness of bulbs. Turning resistance down increases speed of motor and brightness of bulb.
8
Q
P6 - Electricity For Gadgets
What does the voltage current graph look like/show for different resistors?
A
Current through a resistor at a constant temperature is proportional to voltage. Different resistors have different resistances. Straight line graphs are for ohmic resistors which have a constant resistance.
9
Q
P6 - Electricity For Gadgets
What is the voltage current graph like for a filament bulb?
A
As current increases, temperature of filament increases (hence curve). Components with resistance that changes known as non-ohmic resistors.
10
Q
P6 - Electricity For Gadgets
What is the total resistance in a series circuit?
A
Sum of individual resistors
11
Q
P6 - Electricity For Gadgets
How is a circuit with resistors in parallel different?
A
Always less total resistance than branch with smallest resistance. Circuit has higher current.
12
Q
P6 - Electricity For Gadgets
What is the rule for voltage across a pair of resistors?
A
Larger share of total resistance, larger share of total voltage.
13
Q
P6 - Electricity For Gadgets
What is the output of the potential divider?
A
Point between two resistors. Output voltage can be varied by swapping one or both resistors for variable resistor.
14
Q
P6 - Electricity For Gadgets
How are potential dividers useful?
A
Allows you to run a device that requires a certain voltage from a battery of a different voltage.
15
Q
P6 - Electricity For Gadgets
What is an LDR?
A
Light Dependent Resistor - in bright light resistance falls, in darkness resistance is highest. Useful for devices like automatic lights and burglar detectors.
16
Q
P6 - Electricity For Gadgets
What are thermistors?
A
In hot conditions, resistance drops. In cool conditions, resistance increases. Useful temperature sensors e.g. Car engine temperature gauges and electronic thermostats.
17
Q
P6 - Electricity For Gadgets
How can you make a temperature sensor?
A
Using a thermistor and a fixed resistor in a potential divider.
18
Q
P6 - Electricity For Gadgets
What is a transistor?
A
Electronic switches which use a small amount of current to control flow of a much larger current.
19
Q
P6 - Electricity For Gadgets
What are the 3 parts of a transistor?
A
Base, collector, emitter
20
Q
P6 - Electricity For Gadgets
What does the base do in a transistor?
A
Switch that controls flow of current, if no current applied to base, it stops current flowing through rest of transistor. When a small current is applied a larger current can flow through collector and emitter. A larger current would damage transistor.
21
Q
P6 - Electricity For Gadgets
What does the collector do in a transistor?
A
Current flows into transistor through collector
22
Q
P6 - Electricity For Gadgets
What does the emitter do in a transistor?
A
Current flows out of transistor through emitter.
23
Q
P6 - Electricity For Gadgets
What is an LED?
A
A diode that gives out light
24
Q
P6 - Electricity For Gadgets
What does a relay do?
A
2 circuits connected by a relay isolates the low voltage electronic system from high voltage mains often needed for the output device.
25
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What is an AND logic gate made from?
2 transistors
26
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Why is a relay safer?
For person using device because you can make sure that any parts that could come into contact with person are in low current sensing circuit.
27
# P6 - Electricity For Gadgets
What is a magnetic field?
A region where magnetic materials (e.g. iron and steel) and also wires carrying current experience a force acting on them.
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Why is an LED better than an incandescent bulb?
It is better to show output because it uses less power and lasts longer.
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# P6 - Electricity For Gadgets
What is the rule for AND gates?
Each input (2 of them) can be either 1 or 0. An AND gate only gives an output of 1 if both the first and second output are 1.
30
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How does a relay work?
When switch in low-current circuit is closed, turns on electromagnet which attracts iron contact on rocker. Rocker pivots and closes contacts in high current circuit - and motor spins. When low-current switch is opened, electromagnet stops pulling, rocker returns and high current circuit is broken again.
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What is the rule for NOT gates?
A NOT gate just has one input - either 1 or 0.
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Where is a magnetic field created?
There is a magnetic field around a straight, current-carrying wire and it is made up of concentric circles with the wire in centre.
33
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What is the rule for NAND gates?
A NAND gate is a combination of NOT and AND. If AND gave an output of 0, a NAND would give 1 (or vice versa).
34
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What is an LED often connected to to protect it?
It is often connected in a series with a resistor to prevent it from being damaged by too large a current flowing through it.
35
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What rule is used to work out the magnetic field?
Right-Hand Thumb Rule (clenched fingers in direction of magnetic field)
36
# P6 - Electricity For Gadgets
What is the rule for OR gates?
Each input (2 of them) can be either 1 or 0. An AND gate only gives an output of 1 if either the first or second is 1.
37
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What happens if you bend the current-carrying wire into a coil?
Circular magnetic fields around sides of loop reinforce each other at centre. More turns in coil, more individual loops reinforce each other even more.
38
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What is the name givento a coil of wire?
Solenoid
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What is an electromagnet?
A magnet whose magnetic field can be turned on or off with an electric current.
40
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What are the rules for NOR gates?
A NOR gate is a combination of a NOT and an OR. If an OR gives an output of 0, a NOR would give 1 (and vice versa)
41
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How can the strength of the magnetic field around a solenoid be increased?
Add a 'soft' iron core in middle of coil.
42
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How can the strength of the electromagnet be increased?
By adding more turns to the solenoid.
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What happens when a current-carrying wire is put between magnetic poles?
2 magnetic fields affect one another - result is a force on wire.
44
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What happens if the current-carrying wire runs along the magnetic field?
It won't experience any force at all.
45
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What happens to the current-carrying wire to get the full force?
Wire has to be at 90 degrees (right angle) to magnetic field.
46
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When does the force on a current-carrying wire get stronger?
If the current or magnetic field is made stronger.
47
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What direction does the force act on a current-carrying wire?
Force always acts in same direction relative to magnetic field of magnets and direction of current in wire. Changing direction of either magnetic field or current will change direction of force.
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What does Fleming's Left Hand Rule tell you?
Which way force acts in a current carrying wire.
49
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What 4 factors speed up the simple electric motor?
More current, more turns on coil, stronger magentic field, a soft iron core in coil.
50
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What does the first finger tell you in Fleming's LHR?
Direction of field (magnetic)
51
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What happens to the forces on a current in a magnetic field if it is on a spindle?
Forces act one up and one down - rotates.
52
# P6 - Electricity For Gadgets
What is the split-ring commutator?
A way of swapping conacts every half turn to keep motor rotating in same direction.
53
# P6 - Electricity For Gadgets
What does the second finger tell you in Fleming's LHR?
Direction of current
54
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How can the direction of the motor be reversed?
Either by swapping polarity of DC supply or swapping magnetic poles over.
55
# P6 - Electricity For Gadgets
What does your thumb tell you in Fleming's LHR?
Direction of force (motion)
56
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Which hand is used to find the force of a motor?
Left Hand
57
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Which hand is used to find the force of a generator?
Right hand
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How are motors made practical?
They use pole pieces which are so curved they form a hollow cylinder - coil spins inside cylinder. Curved pole pieces have a radial magnetic field which increases magnetic field strength around coil, so motor is more efficient.
59
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What is electromagnetic induction?
Creation of a voltage and maybe current in a wire which is experiencing a change in magnetic field.
60
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What happens to if a magnet/conductor is moved in the opposite direction?
Voltage/current will be reversed, similar to if (magnet) polarity is reversed.
61
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How can electromagnetic induction be generated?
Moving a magnet in a coil of wire OR moving a conductor (wire) in a magnetic field. Shifting magnet from side to side creates a bit of current.
62
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How is AC generated?
If you keep magnet/coil moving back and forth, produce a voltage that keeps swapping direction.
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What 4 factors affect the size of the induced voltage?
Strength of magnet. Area of coil. Number of turns on coil. Speed of movement.
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How is AC generated by turning a magnet?
Turning a magnet end to end in a coil creates a current that lasts as long as you spin magnet. As magnet turns, magnetic field through coil changes - this change in magnetic field induces a voltage which makes a current flow. After 1/2 turn, magnetic field direction reverses and this reverses voltage, current flows in opposite direction around coil of wire. Keep turning magnet in same direction and voltage changes each 1/2 turn - AC.
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What do you get if you increase the speed of the magnet?
If turned faster, higher peak voltage, but also higher frequency - because magnetic field is reversing more frequently.
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How does a generator work?
Rotate a coil in a magnetic field. As coil/magnet spins, current is induced in coil. Current changes direction every half turn.
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What do generators have instead of split-ring commutators?
Slip rings and brushes so contacts don’t swap every half turn.
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What current do generators produce?
AC
69
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What do faster revolutions produce in a generator?
More peaks and higher overall voltage.
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What are dynamos?
Different type of generator. They rotate magent instead of coil to produce AC.
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How is electricity in a power station generated?
Rotating an electromagnet in a coil of wire.
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How can the size of the output voltage be changed in a dynamo?
Adding more turns to electromagnetic coil.
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How can the size and frequency of the output voltage be changed in a dynamo?
By rotating electromagnet coil faster.
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What are transformers?
2 coils of wire round iron core. Used to change size of an alternating voltage. There are 3 types.
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What is a step up transformer?
They step up voltage. Have more turns on secondary coil than primary coil.
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What is a step down transformer?
Step voltage down. Have more turns on primary coil than secondary.
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What is an isolating transformer?
Don’t change voltage at all. Have same number of turns on primary and secondary coils.
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How does a transformer work?
Primary coil produces magnetic field which stays within iron core, meaning nearly all passes through secondary coil and hardly any lost. Because AC in primary coil, current in iron core constantly changing direction - it is a changing magnetic field and this is felt by secondary coil. Changing field induces an alternating voltage in secondary coil (with same frequency) - electromagnetic induction.
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What determines the size of the voltage induced in the secondary coil in a transformer?
Relative number of turns on 2 coils determines whether voltage induced in secondary coil will be greater or less than voltage in primary.
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Why doesn’t a transformer work with DC?
Only work with AC. If supplied DC, get nothing from secondary coil. Would be a magnetic field in iron core, but wouldn’t be constantly changing so there'd be no induction in secondary coil because you need a changing field to induce a voltage.
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What do you have to assume with transformers?
It is 100% efficient
82
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How can power in = power out be re-written?
VpIp = VsIs
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What is the formula for power supplied?
Power = voltage x current P = V x I
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What is the equation to calculate output voltage from a transformer?
Primary voltage ÷ secondary voltage = number of turns on primary ÷ number of turns on secondary
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What is needed to transmit a lot of power?
Either a high voltage or high current
86
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What is the problem with a high current?
Loss (heat) due to resistance of cables (and transformers)
87
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What is the formula for power loss?
Power loss = current² x resistance P = I²R
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What is the significance of the I² in powerloss?
If current is 10x bigger, losses will be 100x bigger. Makes it cheaper to boost voltage to 400,000V and keep current very low.
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Why do transformers have to step the voltage up and down?
For efficient transmission
90
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Where can isolating transformers be used?
In some mains circuits in home, such as bathroom shaver socket.
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What is the purpose of isolating transformers?
Safety. Mains circuit connected to earth so if you touch live parts and ground, you complete circuit. Isolating transformers allow shaver to be used without being physically connected to mains. Minimises risk of live parts touching earth lead - less risk of electrocution.
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What do diodes do?
Only let current flow freely in one direction - very high resistance in other direction. Can tell direction of current from circuit symbol (triangle points in direction of current)
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What are diodes made from?
Semiconductors such as silicon, meaning they can conduct electricity, just not as well as a conductor. 2 different types of silicon joined together at a p-n junction.
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What is the n-type semiconductor in a diode?
1/2 diode made from silicon - impurity added to provide extra free electrons (n = negative charge of electrons)
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What is the p-type semiconductor in a diode?
P = positive charge of holes. Different impurity added to this half so fewer free electrons than normal. Lots of empty spaces left by missing electrons - called holes.
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What happens in the diode when there is no voltage?
Electrons and holes recombine where 2 parts of diode join. Creates region with no holes/free electrons, which acts as an electrical insulator.
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Why is the direction very important when there is a voltage across a diode?
Applying voltage in RIGHT direction means free holes and electrons have enough energy to get across insulating region to other side - CURRENT flows. Applying voltage in WRONG direction means free holes and electrons pulled away from insulating region so stay on same side - NO CURRENT FLOWS.
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What is half-wave rectification?
A single diode only lets through current in half of cycle.
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What needs to be done to get full-wave rectification?
Bridge circuit with 4 diodes. Current always flows through component in same direction, output voltage always has same sign.
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How do you charge a capacitor?
By connecting it to source of voltage e.g. battery. Current flows around circuit and charge gets stored on capacitor.
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What happens to the flow of current after time in a capacitor?
Flow of current decreases.
102
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What happens to a capacitor when the voltage across it is equal?
When voltage is equal to that of battery, current stops and capacitor fully charged. Voltage across capacitor won't rise above voltage of battery.
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What happens if the battery is removed from a circuit with a capacitor?
Capacitor discharges - flow of current is same for discharging as charging but current flows in opposite direction around circuit.
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What are the benefits to makers if electronic components get smaller?
Smaller devices use less raw materials. Most customers like smaller devices.
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What are the benefits to users if electronic components get smaller?
More portable electronic devices available. More powerful and feature-filled devices produced.
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What are the drawbacks to makers if electronic components get smaller?
Can be more complex to produce small devices, and more expensive.
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What are the drawbacks to users if electronic components get smaller?
Smaller devices can be more expensive - easier to lose.
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Flow of charge (electrons) round circuit. Only flows through a component if there is a voltage across that component. Measured in amps, A.
What is current?
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It pushes the current around. It is measured in volts V.
What is voltage?
110
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Anything in the circuit that reduces current and is measured in ohms.
What is resistance?
111
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Collisions in a conductor. Electrons flow through a conductor and collide with metal atoms causing resistance. Collisions cause atoms to vibrate and more they get in way. Increased collisions means increased resistance and temperature of conductor.
What causes resistance?
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More resistance, less current. Because longer wires have more atoms - electrons will collide.
What is resistance like in longer wires?
113
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(Or rheostat) is a resistor whose resistance can be changed. Great for controlling current.
What is a variable resistor?
114
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Controlling speed of motors and brightness of bulbs. Turning resistance down increases speed of motor and brightness of bulb.
What are variable resistors used for?
115
# P6 - Electricity For Gadgets
Current through a resistor at a constant temperature is proportional to voltage. Different resistors have different resistances. Straight line graphs are for ohmic resistors which have a constant resistance.
What does the voltage current graph look like/show for different resistors?
116
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As current increases, temperature of filament increases (hence curve). Components with resistance that changes known as non-ohmic resistors.
What is the voltage current graph like for a filament bulb?
117
# P6 - Electricity For Gadgets
Sum of individual resistors
What is the total resistance in a series circuit?
118
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Always less total resistance than branch with smallest resistance. Circuit has higher current.
How is a circuit with resistors in parallel different?
119
# P6 - Electricity For Gadgets
Larger share of total resistance, larger share of total voltage.
What is the rule for voltage across a pair of resistors?
120
# P6 - Electricity For Gadgets
Point between two resistors. Output voltage can be varied by swapping one or both resistors for variable resistor.
What is the output of the potential divider?
121
# P6 - Electricity For Gadgets
Allows you to run a device that requires a certain voltage from a battery of a different voltage.
How are potential dividers useful?
122
# P6 - Electricity For Gadgets
Light Dependent Resistor - in bright light resistance falls, in darkness resistance is highest. Useful for devices like automatic lights and burglar detectors.
What is an LDR?
123
# P6 - Electricity For Gadgets
In hot conditions, resistance drops. In cool conditions, resistance increases. Useful temperature sensors e.g. Car engine temperature gauges and electronic thermostats.
What are thermistors?
124
# P6 - Electricity For Gadgets
Using a thermistor and a fixed resistor in a potential divider.
How can you make a temperature sensor?
125
# P6 - Electricity For Gadgets
Electronic switches which use a small amount of current to control flow of a much larger current.
What is a transistor?
126
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Base, collector, emitter
What are the 3 parts of a transistor?
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Switch that controls flow of current, if no current applied to base, it stops current flowing through rest of transistor. When a small current is applied a larger current can flow through collector and emitter. A larger current would damage transistor.
What does the base do in a transistor?
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Current flows into transistor through collector
What does the collector do in a transistor?
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Current flows out of transistor through emitter.
What does the emitter do in a transistor?
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A diode that gives out light
What is an LED?
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2 circuits connected by a relay isolates the low voltage electronic system from high voltage mains often needed for the output device.
What does a relay do?
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2 transistors
What is an AND logic gate made from?
133
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For person using device because you can make sure that any parts that could come into contact with person are in low current sensing circuit.
Why is a relay safer?
134
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A region where magnetic materials (e.g. iron and steel) and also wires carrying current experience a force acting on them.
What is a magnetic field?
135
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It is better to show output because it uses less power and lasts longer.
Why is an LED better than an incandescent bulb?
136
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Each input (2 of them) can be either 1 or 0. An AND gate only gives an output of 1 if both the first and second output are 1.
What is the rule for AND gates?
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When switch in low-current circuit is closed, turns on electromagnet which attracts iron contact on rocker. Rocker pivots and closes contacts in high current circuit - and motor spins. When low-current switch is opened, electromagnet stops pulling, rocker returns and high current circuit is broken again.
How does a relay work?
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A NOT gate just has one input - either 1 or 0.
What is the rule for NOT gates?
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There is a magnetic field around a straight, current-carrying wire and it is made up of concentric circles with the wire in centre.
Where is a magnetic field created?
140
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A NAND gate is a combination of NOT and AND. If AND gave an output of 0, a NAND would give 1 (or vice versa).
What is the rule for NAND gates?
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It is often connected in a series with a resistor to prevent it from being damaged by too large a current flowing through it.
What is an LED often connected to to protect it?
142
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Right-Hand Thumb Rule (clenched fingers in direction of magnetic field)
What rule is used to work out the magnetic field?
143
# P6 - Electricity For Gadgets
Each input (2 of them) can be either 1 or 0. An AND gate only gives an output of 1 if either the first or second is 1.
What is the rule for OR gates?
144
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Circular magnetic fields around sides of loop reinforce each other at centre. More turns in coil, more individual loops reinforce each other even more.
What happens if you bend the current-carrying wire into a coil?
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Solenoid
What is the name givento a coil of wire?
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A magnet whose magnetic field can be turned on or off with an electric current.
What is an electromagnet?
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A NOR gate is a combination of a NOT and an OR. If an OR gives an output of 0, a NOR would give 1 (and vice versa)
What are the rules for NOR gates?
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Add a 'soft' iron core in middle of coil.
How can the strength of the magnetic field around a solenoid be increased?
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By adding more turns to the solenoid.
How can the strength of the electromagnet be increased?
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2 magnetic fields affect one another - result is a force on wire.
What happens when a current-carrying wire is put between magnetic poles?
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It won't experience any force at all.
What happens if the current-carrying wire runs along the magnetic field?
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Wire has to be at 90 degrees (right angle) to magnetic field.
What happens to the current-carrying wire to get the full force?
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If the current or magnetic field is made stronger.
When does the force on a current-carrying wire get stronger?
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Force always acts in same direction relative to magnetic field of magnets and direction of current in wire. Changing direction of either magnetic field or current will change direction of force.
What direction does the force act on a current-carrying wire?
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Which way force acts in a current carrying wire.
What does Fleming's Left Hand Rule tell you?
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More current, more turns on coil, stronger magentic field, a soft iron core in coil.
What 4 factors speed up the simple electric motor?
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Direction of field (magnetic)
What does the first finger tell you in Fleming's LHR?
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Forces act one up and one down - rotates.
What happens to the forces on a current in a magnetic field if it is on a spindle?
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A way of swapping conacts every half turn to keep motor rotating in same direction.
What is the split-ring commutator?
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Direction of current
What does the second finger tell you in Fleming's LHR?
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Either by swapping polarity of DC supply or swapping magnetic poles over.
How can the direction of the motor be reversed?
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Direction of force (motion)
What does your thumb tell you in Fleming's LHR?
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Left Hand
Which hand is used to find the force of a motor?
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Right hand
Which hand is used to find the force of a generator?
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They use pole pieces which are so curved they form a hollow cylinder - coil spins inside cylinder. Curved pole pieces have a radial magnetic field which increases magnetic field strength around coil, so motor is more efficient.
How are motors made practical?
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Creation of a voltage and maybe current in a wire which is experiencing a change in magnetic field.
What is electromagnetic induction?
167
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Voltage/current will be reversed, similar to if (magnet) polarity is reversed.
What happens to if a magnet/conductor is moved in the opposite direction?
168
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Moving a magnet in a coil of wire OR moving a conductor (wire) in a magnetic field. Shifting magnet from side to side creates a bit of current.
How can electromagnetic induction be generated?
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If you keep magnet/coil moving back and forth, produce a voltage that keeps swapping direction.
How is AC generated?
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Strength of magnet. Area of coil. Number of turns on coil. Speed of movement.
What 4 factors affect the size of the induced voltage?
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Turning a magnet end to end in a coil creates a current that lasts as long as you spin magnet. As magnet turns, magnetic field through coil changes - this change in magnetic field induces a voltage which makes a current flow. After 1/2 turn, magnetic field direction reverses and this reverses voltage, current flows in opposite direction around coil of wire. Keep turning magnet in same direction and voltage changes each 1/2 turn - AC.
How is AC generated by turning a magnet?
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If turned faster, higher peak voltage, but also higher frequency - because magnetic field is reversing more frequently.
What do you get if you increase the speed of the magnet?
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Rotate a coil in a magnetic field. As coil/magnet spins, current is induced in coil. Current changes direction every half turn.
How does a generator work?
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Slip rings and brushes so contacts don’t swap every half turn.
What do generators have instead of split-ring commutators?
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AC
What current do generators produce?
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More peaks and higher overall voltage.
What do faster revolutions produce in a generator?
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Different type of generator. They rotate magent instead of coil to produce AC.
What are dynamos?
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Rotating an electromagnet in a coil of wire.
How is electricity in a power station generated?
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Adding more turns to electromagnetic coil.
How can the size of the output voltage be changed in a dynamo?
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By rotating electromagnet coil faster.
How can the size and frequency of the output voltage be changed in a dynamo?
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2 coils of wire round iron core. Used to change size of an alternating voltage. There are 3 types.
What are transformers?
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They step up voltage. Have more turns on secondary coil than primary coil.
What is a step up transformer?
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Step voltage down. Have more turns on primary coil than secondary.
What is a step down transformer?
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Don’t change voltage at all. Have same number of turns on primary and secondary coils.
What is an isolating transformer?
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Primary coil produces magnetic field which stays within iron core, meaning nearly all passes through secondary coil and hardly any lost. Because AC in primary coil, current in iron core constantly changing direction - it is a changing magnetic field and this is felt by secondary coil. Changing field induces an alternating voltage in secondary coil (with same frequency) - electromagnetic induction.
How does a transformer work?
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Relative number of turns on 2 coils determines whether voltage induced in secondary coil will be greater or less than voltage in primary.
What determines the size of the voltage induced in the secondary coil in a transformer?
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Only work with AC. If supplied DC, get nothing from secondary coil. Would be a magnetic field in iron core, but wouldn’t be constantly changing so there'd be no induction in secondary coil because you need a changing field to induce a voltage.
Why doesn’t a transformer work with DC?
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It is 100% efficient
What do you have to assume with transformers?
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VpIp = VsIs
How can power in = power out be re-written?
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Power = voltage x current P = V x I
What is the formula for power supplied?
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Primary voltage ÷ secondary voltage = number of turns on primary ÷ number of turns on secondary
What is the equation to calculate output voltage from a transformer?
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Either a high voltage or high current
What is needed to transmit a lot of power?
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Loss (heat) due to resistance of cables (and transformers)
What is the problem with a high current?
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Power loss = current² x resistance P = I²R
What is the formula for power loss?
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If current is 10x bigger, losses will be 100x bigger. Makes it cheaper to boost voltage to 400,000V and keep current very low.
What is the significance of the I² in powerloss?
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For efficient transmission
Why do transformers have to step the voltage up and down?
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In some mains circuits in home, such as bathroom shaver socket.
Where can isolating transformers be used?
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Safety. Mains circuit connected to earth so if you touch live parts and ground, you complete circuit. Isolating transformers allow shaver to be used without being physically connected to mains. Minimises risk of live parts touching earth lead - less risk of electrocution.
What is the purpose of isolating transformers?
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Only let current flow freely in one direction - very high resistance in other direction. Can tell direction of current from circuit symbol (triangle points in direction of current)
What do diodes do?
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Semiconductors such as silicon, meaning they can conduct electricity, just not as well as a conductor. 2 different types of silicon joined together at a p-n junction.
What are diodes made from?
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1/2 diode made from silicon - impurity added to provide extra free electrons (n = negative charge of electrons)
What is the n-type semiconductor in a diode?
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P = positive charge of holes. Different impurity added to this half so fewer free electrons than normal. Lots of empty spaces left by missing electrons - called holes.
What is the p-type semiconductor in a diode?
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Electrons and holes recombine where 2 parts of diode join. Creates region with no holes/free electrons, which acts as an electrical insulator.
What happens in the diode when there is no voltage?
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Applying voltage in RIGHT direction means free holes and electrons have enough energy to get across insulating region to other side - CURRENT flows. Applying voltage in WRONG direction means free holes and electrons pulled away from insulating region so stay on same side - NO CURRENT FLOWS.
Why is the direction very important when there is a voltage across a diode?
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A single diode only lets through current in half of cycle.
What is half-wave rectification?
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Bridge circuit with 4 diodes. Current always flows through component in same direction, output voltage always has same sign.
What needs to be done to get full-wave rectification?
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By connecting it to source of voltage e.g. battery. Current flows around circuit and charge gets stored on capacitor.
How do you charge a capacitor?
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Flow of current decreases.
What happens to the flow of current after time in a capacitor?
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When voltage is equal to that of battery, current stops and capacitor fully charged. Voltage across capacitor won't rise above voltage of battery.
What happens to a capacitor when the voltage across it is equal?
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Capacitor discharges - flow of current is same for discharging as charging but current flows in opposite direction around circuit.
What happens if the battery is removed from a circuit with a capacitor?
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Smaller devices use less raw materials. Most customers like smaller devices.
What are the benefits to makers if electronic components get smaller?
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More portable electronic devices available. More powerful and feature-filled devices produced.
What are the benefits to users if electronic components get smaller?
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Can be more complex to produce small devices, and more expensive.
What are the drawbacks to makers if electronic components get smaller?
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Smaller devices can be more expensive - easier to lose.
What are the drawbacks to users if electronic components get smaller?
