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Physics GCSE OCR Gateway B > P6 - Electricity For Gadgets > Flashcards

P6 - Electricity For Gadgets Flashcards

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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.

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2
Q

P6 - Electricity For Gadgets

What is voltage?

A

It pushes the current around. It is measured in volts V.

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3
Q

P6 - Electricity For Gadgets

What is resistance?

A

Anything in the circuit that reduces current and is measured in ohms.

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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.

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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.

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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.

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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.

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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.

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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.

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10
Q

P6 - Electricity For Gadgets

What is the total resistance in a series circuit?

A

Sum of individual resistors

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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19
Q

P6 - Electricity For Gadgets

What are the 3 parts of a transistor?

A

Base, collector, emitter

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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.

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21
Q

P6 - Electricity For Gadgets

What does the collector do in a transistor?

A

Current flows into transistor through collector

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22
Q

P6 - Electricity For Gadgets

What does the emitter do in a transistor?

A

Current flows out of transistor through emitter.

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23
Q

P6 - Electricity For Gadgets

What is an LED?

A

A diode that gives out light

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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.

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25
Q

P6 - Electricity For Gadgets

What is an AND logic gate made from?

A

2 transistors

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26
Q

P6 - Electricity For Gadgets

Why is a relay safer?

A

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.

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27
Q

P6 - Electricity For Gadgets

What is a magnetic field?

A

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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28
Q

P6 - Electricity For Gadgets

Why is an LED better than an incandescent bulb?

A

It is better to show output because it uses less power and lasts longer.

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29
Q

P6 - Electricity For Gadgets

What is the rule for AND gates?

A

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.

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30
Q

P6 - Electricity For Gadgets

How does a relay work?

A

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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31
Q

P6 - Electricity For Gadgets

What is the rule for NOT gates?

A

A NOT gate just has one input - either 1 or 0.

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32
Q

P6 - Electricity For Gadgets

Where is a magnetic field created?

A

There is a magnetic field around a straight, current-carrying wire and it is made up of concentric circles with the wire in centre.

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33
Q

P6 - Electricity For Gadgets

What is the rule for NAND gates?

A

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).

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34
Q

P6 - Electricity For Gadgets

What is an LED often connected to to protect it?

A

It is often connected in a series with a resistor to prevent it from being damaged by too large a current flowing through it.

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35
Q

P6 - Electricity For Gadgets

What rule is used to work out the magnetic field?

A

Right-Hand Thumb Rule (clenched fingers in direction of magnetic field)

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36
Q

P6 - Electricity For Gadgets

What is the rule for OR gates?

A

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.

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37
Q

P6 - Electricity For Gadgets

What happens if you bend the current-carrying wire into a coil?

A

Circular magnetic fields around sides of loop reinforce each other at centre. More turns in coil, more individual loops reinforce each other even more.

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38
Q

P6 - Electricity For Gadgets

What is the name givento a coil of wire?

A

Solenoid

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39
Q

P6 - Electricity For Gadgets

What is an electromagnet?

A

A magnet whose magnetic field can be turned on or off with an electric current.

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40
Q

P6 - Electricity For Gadgets

What are the rules for NOR gates?

A

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)

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41
Q

P6 - Electricity For Gadgets

How can the strength of the magnetic field around a solenoid be increased?

A

Add a ‘soft’ iron core in middle of coil.

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42
Q

P6 - Electricity For Gadgets

How can the strength of the electromagnet be increased?

A

By adding more turns to the solenoid.

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43
Q

P6 - Electricity For Gadgets

What happens when a current-carrying wire is put between magnetic poles?

A

2 magnetic fields affect one another - result is a force on wire.

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44
Q

P6 - Electricity For Gadgets

What happens if the current-carrying wire runs along the magnetic field?

A

It won’t experience any force at all.

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45
Q

P6 - Electricity For Gadgets

What happens to the current-carrying wire to get the full force?

A

Wire has to be at 90 degrees (right angle) to magnetic field.

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46
Q

P6 - Electricity For Gadgets

When does the force on a current-carrying wire get stronger?

A

If the current or magnetic field is made stronger.

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47
Q

P6 - Electricity For Gadgets

What direction does the force act on a current-carrying wire?

A

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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48
Q

P6 - Electricity For Gadgets

What does Fleming’s Left Hand Rule tell you?

A

Which way force acts in a current carrying wire.

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49
Q

P6 - Electricity For Gadgets

What 4 factors speed up the simple electric motor?

A

More current, more turns on coil, stronger magentic field, a soft iron core in coil.

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50
Q

P6 - Electricity For Gadgets

What does the first finger tell you in Fleming’s LHR?

A

Direction of field (magnetic)

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51
Q

P6 - Electricity For Gadgets

What happens to the forces on a current in a magnetic field if it is on a spindle?

A

Forces act one up and one down - rotates.

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52
Q

P6 - Electricity For Gadgets

What is the split-ring commutator?

A

A way of swapping conacts every half turn to keep motor rotating in same direction.

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53
Q

P6 - Electricity For Gadgets

What does the second finger tell you in Fleming’s LHR?

A

Direction of current

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54
Q

P6 - Electricity For Gadgets

How can the direction of the motor be reversed?

A

Either by swapping polarity of DC supply or swapping magnetic poles over.

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55
Q

P6 - Electricity For Gadgets

What does your thumb tell you in Fleming’s LHR?

A

Direction of force (motion)

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56
Q

P6 - Electricity For Gadgets

Which hand is used to find the force of a motor?

A

Left Hand

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57
Q

P6 - Electricity For Gadgets

Which hand is used to find the force of a generator?

A

Right hand

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58
Q

P6 - Electricity For Gadgets

How are motors made practical?

A

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.

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59
Q

P6 - Electricity For Gadgets

What is electromagnetic induction?

A

Creation of a voltage and maybe current in a wire which is experiencing a change in magnetic field.

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60
Q

P6 - Electricity For Gadgets

What happens to if a magnet/conductor is moved in the opposite direction?

A

Voltage/current will be reversed, similar to if (magnet) polarity is reversed.

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61
Q

P6 - Electricity For Gadgets

How can electromagnetic induction be generated?

A

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.

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62
Q

P6 - Electricity For Gadgets

How is AC generated?

A

If you keep magnet/coil moving back and forth, produce a voltage that keeps swapping direction.

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63
Q

P6 - Electricity For Gadgets

What 4 factors affect the size of the induced voltage?

A

Strength of magnet. Area of coil. Number of turns on coil. Speed of movement.

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64
Q

P6 - Electricity For Gadgets

How is AC generated by turning a magnet?

A

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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65
Q

P6 - Electricity For Gadgets

What do you get if you increase the speed of the magnet?

A

If turned faster, higher peak voltage, but also higher frequency - because magnetic field is reversing more frequently.

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66
Q

P6 - Electricity For Gadgets

How does a generator work?

A

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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67
Q

P6 - Electricity For Gadgets

What do generators have instead of split-ring commutators?

A

Slip rings and brushes so contacts don’t swap every half turn.

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68
Q

P6 - Electricity For Gadgets

What current do generators produce?

A

AC

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69
Q

P6 - Electricity For Gadgets

What do faster revolutions produce in a generator?

A

More peaks and higher overall voltage.

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70
Q

P6 - Electricity For Gadgets

What are dynamos?

A

Different type of generator. They rotate magent instead of coil to produce AC.

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71
Q

P6 - Electricity For Gadgets

How is electricity in a power station generated?

A

Rotating an electromagnet in a coil of wire.

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72
Q

P6 - Electricity For Gadgets

How can the size of the output voltage be changed in a dynamo?

A

Adding more turns to electromagnetic coil.

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73
Q

P6 - Electricity For Gadgets

How can the size and frequency of the output voltage be changed in a dynamo?

A

By rotating electromagnet coil faster.

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74
Q

P6 - Electricity For Gadgets

What are transformers?

A

2 coils of wire round iron core. Used to change size of an alternating voltage. There are 3 types.

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75
Q

P6 - Electricity For Gadgets

What is a step up transformer?

A

They step up voltage. Have more turns on secondary coil than primary coil.

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76
Q

P6 - Electricity For Gadgets

What is a step down transformer?

A

Step voltage down. Have more turns on primary coil than secondary.

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77
Q

P6 - Electricity For Gadgets

What is an isolating transformer?

A

Don’t change voltage at all. Have same number of turns on primary and secondary coils.

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78
Q

P6 - Electricity For Gadgets

How does a transformer work?

A

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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79
Q

P6 - Electricity For Gadgets

What determines the size of the voltage induced in the secondary coil in a transformer?

A

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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80
Q

P6 - Electricity For Gadgets

Why doesn’t a transformer work with DC?

A

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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81
Q

P6 - Electricity For Gadgets

What do you have to assume with transformers?

A

It is 100% efficient

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82
Q

P6 - Electricity For Gadgets

How can power in = power out be re-written?

A

VpIp = VsIs

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83
Q

P6 - Electricity For Gadgets

What is the formula for power supplied?

A

Power = voltage x current P = V x I

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84
Q

P6 - Electricity For Gadgets

What is the equation to calculate output voltage from a transformer?

A

Primary voltage ÷ secondary voltage = number of turns on primary ÷ number of turns on secondary

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85
Q

P6 - Electricity For Gadgets

What is needed to transmit a lot of power?

A

Either a high voltage or high current

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86
Q

P6 - Electricity For Gadgets

What is the problem with a high current?

A

Loss (heat) due to resistance of cables (and transformers)

87
Q

P6 - Electricity For Gadgets

What is the formula for power loss?

A

Power loss = current² x resistance P = I²R

88
Q

P6 - Electricity For Gadgets

What is the significance of the I² in powerloss?

A

If current is 10x bigger, losses will be 100x bigger. Makes it cheaper to boost voltage to 400,000V and keep current very low.

89
Q

P6 - Electricity For Gadgets

Why do transformers have to step the voltage up and down?

A

For efficient transmission

90
Q

P6 - Electricity For Gadgets

Where can isolating transformers be used?

A

In some mains circuits in home, such as bathroom shaver socket.

91
Q

P6 - Electricity For Gadgets

What is the purpose of isolating transformers?

A

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.

92
Q

P6 - Electricity For Gadgets

What do diodes do?

A

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)

93
Q

P6 - Electricity For Gadgets

What are diodes made from?

A

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.

94
Q

P6 - Electricity For Gadgets

What is the n-type semiconductor in a diode?

A

1/2 diode made from silicon - impurity added to provide extra free electrons (n = negative charge of electrons)

95
Q

P6 - Electricity For Gadgets

What is the p-type semiconductor in a diode?

A

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.

96
Q

P6 - Electricity For Gadgets

What happens in the diode when there is no voltage?

A

Electrons and holes recombine where 2 parts of diode join. Creates region with no holes/free electrons, which acts as an electrical insulator.

97
Q

P6 - Electricity For Gadgets

Why is the direction very important when there is a voltage across a diode?

A

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.

98
Q

P6 - Electricity For Gadgets

What is half-wave rectification?

A

A single diode only lets through current in half of cycle.

99
Q

P6 - Electricity For Gadgets

What needs to be done to get full-wave rectification?

A

Bridge circuit with 4 diodes. Current always flows through component in same direction, output voltage always has same sign.

100
Q

P6 - Electricity For Gadgets

How do you charge a capacitor?

A

By connecting it to source of voltage e.g. battery. Current flows around circuit and charge gets stored on capacitor.

101
Q

P6 - Electricity For Gadgets

What happens to the flow of current after time in a capacitor?

A

Flow of current decreases.

102
Q

P6 - Electricity For Gadgets

What happens to a capacitor when the voltage across it is equal?

A

When voltage is equal to that of battery, current stops and capacitor fully charged. Voltage across capacitor won’t rise above voltage of battery.

103
Q

P6 - Electricity For Gadgets

What happens if the battery is removed from a circuit with a capacitor?

A

Capacitor discharges - flow of current is same for discharging as charging but current flows in opposite direction around circuit.

104
Q

P6 - Electricity For Gadgets

What are the benefits to makers if electronic components get smaller?

A

Smaller devices use less raw materials. Most customers like smaller devices.

105
Q

P6 - Electricity For Gadgets

What are the benefits to users if electronic components get smaller?

A

More portable electronic devices available. More powerful and feature-filled devices produced.

106
Q

P6 - Electricity For Gadgets

What are the drawbacks to makers if electronic components get smaller?

A

Can be more complex to produce small devices, and more expensive.

107
Q

P6 - Electricity For Gadgets

What are the drawbacks to users if electronic components get smaller?

A

Smaller devices can be more expensive - easier to lose.

108
Q

P6 - Electricity For Gadgets

Flow of charge (electrons) round circuit. Only flows through a component if there is a voltage across that component. Measured in amps, A.

A

What is current?

109
Q

P6 - Electricity For Gadgets

It pushes the current around. It is measured in volts V.

A

What is voltage?

110
Q

P6 - Electricity For Gadgets

Anything in the circuit that reduces current and is measured in ohms.

A

What is resistance?

111
Q

P6 - Electricity For Gadgets

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.

A

What causes resistance?

112
Q

P6 - Electricity For Gadgets

More resistance, less current. Because longer wires have more atoms - electrons will collide.

A

What is resistance like in longer wires?

113
Q

P6 - Electricity For Gadgets

(Or rheostat) is a resistor whose resistance can be changed. Great for controlling current.

A

What is a variable resistor?

114
Q

P6 - Electricity For Gadgets

Controlling speed of motors and brightness of bulbs. Turning resistance down increases speed of motor and brightness of bulb.

A

What are variable resistors used for?

115
Q

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.

A

What does the voltage current graph look like/show for different resistors?

116
Q

P6 - Electricity For Gadgets

As current increases, temperature of filament increases (hence curve). Components with resistance that changes known as non-ohmic resistors.

A

What is the voltage current graph like for a filament bulb?

117
Q

P6 - Electricity For Gadgets

Sum of individual resistors

A

What is the total resistance in a series circuit?

118
Q

P6 - Electricity For Gadgets

Always less total resistance than branch with smallest resistance. Circuit has higher current.

A

How is a circuit with resistors in parallel different?

119
Q

P6 - Electricity For Gadgets

Larger share of total resistance, larger share of total voltage.

A

What is the rule for voltage across a pair of resistors?

120
Q

P6 - Electricity For Gadgets

Point between two resistors. Output voltage can be varied by swapping one or both resistors for variable resistor.

A

What is the output of the potential divider?

121
Q

P6 - Electricity For Gadgets

Allows you to run a device that requires a certain voltage from a battery of a different voltage.

A

How are potential dividers useful?

122
Q

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.

A

What is an LDR?

123
Q

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.

A

What are thermistors?

124
Q

P6 - Electricity For Gadgets

Using a thermistor and a fixed resistor in a potential divider.

A

How can you make a temperature sensor?

125
Q

P6 - Electricity For Gadgets

Electronic switches which use a small amount of current to control flow of a much larger current.

A

What is a transistor?

126
Q

P6 - Electricity For Gadgets

Base, collector, emitter

A

What are the 3 parts of a transistor?

127
Q

P6 - Electricity For Gadgets

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.

A

What does the base do in a transistor?

128
Q

P6 - Electricity For Gadgets

Current flows into transistor through collector

A

What does the collector do in a transistor?

129
Q

P6 - Electricity For Gadgets

Current flows out of transistor through emitter.

A

What does the emitter do in a transistor?

130
Q

P6 - Electricity For Gadgets

A diode that gives out light

A

What is an LED?

131
Q

P6 - Electricity For Gadgets

2 circuits connected by a relay isolates the low voltage electronic system from high voltage mains often needed for the output device.

A

What does a relay do?

132
Q

P6 - Electricity For Gadgets

2 transistors

A

What is an AND logic gate made from?

133
Q

P6 - Electricity For Gadgets

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.

A

Why is a relay safer?

134
Q

P6 - Electricity For Gadgets

A region where magnetic materials (e.g. iron and steel) and also wires carrying current experience a force acting on them.

A

What is a magnetic field?

135
Q

P6 - Electricity For Gadgets

It is better to show output because it uses less power and lasts longer.

A

Why is an LED better than an incandescent bulb?

136
Q

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 both the first and second output are 1.

A

What is the rule for AND gates?

137
Q

P6 - Electricity For Gadgets

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.

A

How does a relay work?

138
Q

P6 - Electricity For Gadgets

A NOT gate just has one input - either 1 or 0.

A

What is the rule for NOT gates?

139
Q

P6 - Electricity For Gadgets

There is a magnetic field around a straight, current-carrying wire and it is made up of concentric circles with the wire in centre.

A

Where is a magnetic field created?

140
Q

P6 - Electricity For Gadgets

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).

A

What is the rule for NAND gates?

141
Q

P6 - Electricity For Gadgets

It is often connected in a series with a resistor to prevent it from being damaged by too large a current flowing through it.

A

What is an LED often connected to to protect it?

142
Q

P6 - Electricity For Gadgets

Right-Hand Thumb Rule (clenched fingers in direction of magnetic field)

A

What rule is used to work out the magnetic field?

143
Q

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.

A

What is the rule for OR gates?

144
Q

P6 - Electricity For Gadgets

Circular magnetic fields around sides of loop reinforce each other at centre. More turns in coil, more individual loops reinforce each other even more.

A

What happens if you bend the current-carrying wire into a coil?

145
Q

P6 - Electricity For Gadgets

Solenoid

A

What is the name givento a coil of wire?

146
Q

P6 - Electricity For Gadgets

A magnet whose magnetic field can be turned on or off with an electric current.

A

What is an electromagnet?

147
Q

P6 - Electricity For Gadgets

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)

A

What are the rules for NOR gates?

148
Q

P6 - Electricity For Gadgets

Add a ‘soft’ iron core in middle of coil.

A

How can the strength of the magnetic field around a solenoid be increased?

149
Q

P6 - Electricity For Gadgets

By adding more turns to the solenoid.

A

How can the strength of the electromagnet be increased?

150
Q

P6 - Electricity For Gadgets

2 magnetic fields affect one another - result is a force on wire.

A

What happens when a current-carrying wire is put between magnetic poles?

151
Q

P6 - Electricity For Gadgets

It won’t experience any force at all.

A

What happens if the current-carrying wire runs along the magnetic field?

152
Q

P6 - Electricity For Gadgets

Wire has to be at 90 degrees (right angle) to magnetic field.

A

What happens to the current-carrying wire to get the full force?

153
Q

P6 - Electricity For Gadgets

If the current or magnetic field is made stronger.

A

When does the force on a current-carrying wire get stronger?

154
Q

P6 - Electricity For Gadgets

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.

A

What direction does the force act on a current-carrying wire?

155
Q

P6 - Electricity For Gadgets

Which way force acts in a current carrying wire.

A

What does Fleming’s Left Hand Rule tell you?

156
Q

P6 - Electricity For Gadgets

More current, more turns on coil, stronger magentic field, a soft iron core in coil.

A

What 4 factors speed up the simple electric motor?

157
Q

P6 - Electricity For Gadgets

Direction of field (magnetic)

A

What does the first finger tell you in Fleming’s LHR?

158
Q

P6 - Electricity For Gadgets

Forces act one up and one down - rotates.

A

What happens to the forces on a current in a magnetic field if it is on a spindle?

159
Q

P6 - Electricity For Gadgets

A way of swapping conacts every half turn to keep motor rotating in same direction.

A

What is the split-ring commutator?

160
Q

P6 - Electricity For Gadgets

Direction of current

A

What does the second finger tell you in Fleming’s LHR?

161
Q

P6 - Electricity For Gadgets

Either by swapping polarity of DC supply or swapping magnetic poles over.

A

How can the direction of the motor be reversed?

162
Q

P6 - Electricity For Gadgets

Direction of force (motion)

A

What does your thumb tell you in Fleming’s LHR?

163
Q

P6 - Electricity For Gadgets

Left Hand

A

Which hand is used to find the force of a motor?

164
Q

P6 - Electricity For Gadgets

Right hand

A

Which hand is used to find the force of a generator?

165
Q

P6 - Electricity For Gadgets

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.

A

How are motors made practical?

166
Q

P6 - Electricity For Gadgets

Creation of a voltage and maybe current in a wire which is experiencing a change in magnetic field.

A

What is electromagnetic induction?

167
Q

P6 - Electricity For Gadgets

Voltage/current will be reversed, similar to if (magnet) polarity is reversed.

A

What happens to if a magnet/conductor is moved in the opposite direction?

168
Q

P6 - Electricity For Gadgets

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.

A

How can electromagnetic induction be generated?

169
Q

P6 - Electricity For Gadgets

If you keep magnet/coil moving back and forth, produce a voltage that keeps swapping direction.

A

How is AC generated?

170
Q

P6 - Electricity For Gadgets

Strength of magnet. Area of coil. Number of turns on coil. Speed of movement.

A

What 4 factors affect the size of the induced voltage?

171
Q

P6 - Electricity For Gadgets

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.

A

How is AC generated by turning a magnet?

172
Q

P6 - Electricity For Gadgets

If turned faster, higher peak voltage, but also higher frequency - because magnetic field is reversing more frequently.

A

What do you get if you increase the speed of the magnet?

173
Q

P6 - Electricity For Gadgets

Rotate a coil in a magnetic field. As coil/magnet spins, current is induced in coil. Current changes direction every half turn.

A

How does a generator work?

174
Q

P6 - Electricity For Gadgets

Slip rings and brushes so contacts don’t swap every half turn.

A

What do generators have instead of split-ring commutators?

175
Q

P6 - Electricity For Gadgets

AC

A

What current do generators produce?

176
Q

P6 - Electricity For Gadgets

More peaks and higher overall voltage.

A

What do faster revolutions produce in a generator?

177
Q

P6 - Electricity For Gadgets

Different type of generator. They rotate magent instead of coil to produce AC.

A

What are dynamos?

178
Q

P6 - Electricity For Gadgets

Rotating an electromagnet in a coil of wire.

A

How is electricity in a power station generated?

179
Q

P6 - Electricity For Gadgets

Adding more turns to electromagnetic coil.

A

How can the size of the output voltage be changed in a dynamo?

180
Q

P6 - Electricity For Gadgets

By rotating electromagnet coil faster.

A

How can the size and frequency of the output voltage be changed in a dynamo?

181
Q

P6 - Electricity For Gadgets

2 coils of wire round iron core. Used to change size of an alternating voltage. There are 3 types.

A

What are transformers?

182
Q

P6 - Electricity For Gadgets

They step up voltage. Have more turns on secondary coil than primary coil.

A

What is a step up transformer?

183
Q

P6 - Electricity For Gadgets

Step voltage down. Have more turns on primary coil than secondary.

A

What is a step down transformer?

184
Q

P6 - Electricity For Gadgets

Don’t change voltage at all. Have same number of turns on primary and secondary coils.

A

What is an isolating transformer?

185
Q

P6 - Electricity For Gadgets

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.

A

How does a transformer work?

186
Q

P6 - Electricity For Gadgets

Relative number of turns on 2 coils determines whether voltage induced in secondary coil will be greater or less than voltage in primary.

A

What determines the size of the voltage induced in the secondary coil in a transformer?

187
Q

P6 - Electricity For Gadgets

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.

A

Why doesn’t a transformer work with DC?

188
Q

P6 - Electricity For Gadgets

It is 100% efficient

A

What do you have to assume with transformers?

189
Q

P6 - Electricity For Gadgets

VpIp = VsIs

A

How can power in = power out be re-written?

190
Q

P6 - Electricity For Gadgets

Power = voltage x current P = V x I

A

What is the formula for power supplied?

191
Q

P6 - Electricity For Gadgets

Primary voltage ÷ secondary voltage = number of turns on primary ÷ number of turns on secondary

A

What is the equation to calculate output voltage from a transformer?

192
Q

P6 - Electricity For Gadgets

Either a high voltage or high current

A

What is needed to transmit a lot of power?

193
Q

P6 - Electricity For Gadgets

Loss (heat) due to resistance of cables (and transformers)

A

What is the problem with a high current?

194
Q

P6 - Electricity For Gadgets

Power loss = current² x resistance P = I²R

A

What is the formula for power loss?

195
Q

P6 - Electricity For Gadgets

If current is 10x bigger, losses will be 100x bigger. Makes it cheaper to boost voltage to 400,000V and keep current very low.

A

What is the significance of the I² in powerloss?

196
Q

P6 - Electricity For Gadgets

For efficient transmission

A

Why do transformers have to step the voltage up and down?

197
Q

P6 - Electricity For Gadgets

In some mains circuits in home, such as bathroom shaver socket.

A

Where can isolating transformers be used?

198
Q

P6 - Electricity For Gadgets

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.

A

What is the purpose of isolating transformers?

199
Q

P6 - Electricity For Gadgets

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)

A

What do diodes do?

200
Q

P6 - Electricity For Gadgets

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.

A

What are diodes made from?

201
Q

P6 - Electricity For Gadgets

1/2 diode made from silicon - impurity added to provide extra free electrons (n = negative charge of electrons)

A

What is the n-type semiconductor in a diode?

202
Q

P6 - Electricity For Gadgets

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.

A

What is the p-type semiconductor in a diode?

203
Q

P6 - Electricity For Gadgets

Electrons and holes recombine where 2 parts of diode join. Creates region with no holes/free electrons, which acts as an electrical insulator.

A

What happens in the diode when there is no voltage?

204
Q

P6 - Electricity For Gadgets

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.

A

Why is the direction very important when there is a voltage across a diode?

205
Q

P6 - Electricity For Gadgets

A single diode only lets through current in half of cycle.

A

What is half-wave rectification?

206
Q

P6 - Electricity For Gadgets

Bridge circuit with 4 diodes. Current always flows through component in same direction, output voltage always has same sign.

A

What needs to be done to get full-wave rectification?

207
Q

P6 - Electricity For Gadgets

By connecting it to source of voltage e.g. battery. Current flows around circuit and charge gets stored on capacitor.

A

How do you charge a capacitor?

208
Q

P6 - Electricity For Gadgets

Flow of current decreases.

A

What happens to the flow of current after time in a capacitor?

209
Q

P6 - Electricity For Gadgets

When voltage is equal to that of battery, current stops and capacitor fully charged. Voltage across capacitor won’t rise above voltage of battery.

A

What happens to a capacitor when the voltage across it is equal?

210
Q

P6 - Electricity For Gadgets

Capacitor discharges - flow of current is same for discharging as charging but current flows in opposite direction around circuit.

A

What happens if the battery is removed from a circuit with a capacitor?

211
Q

P6 - Electricity For Gadgets

Smaller devices use less raw materials. Most customers like smaller devices.

A

What are the benefits to makers if electronic components get smaller?

212
Q

P6 - Electricity For Gadgets

More portable electronic devices available. More powerful and feature-filled devices produced.

A

What are the benefits to users if electronic components get smaller?

213
Q

P6 - Electricity For Gadgets

Can be more complex to produce small devices, and more expensive.

A

What are the drawbacks to makers if electronic components get smaller?

214
Q

P6 - Electricity For Gadgets

Smaller devices can be more expensive - easier to lose.

A

What are the drawbacks to users if electronic components get smaller?

Physics GCSE OCR Gateway B (7 decks)

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