P6 - Electricity For Gadgets

Question 1

P6 - Electricity For Gadgets

What is current?

Answer 1

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

Question 2

P6 - Electricity For Gadgets

What is voltage?

Answer 2

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

Question 3

P6 - Electricity For Gadgets

What is resistance?

Answer 3

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

Question 4

P6 - Electricity For Gadgets

What causes resistance?

Answer 4

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.

Question 5

P6 - Electricity For Gadgets

What is resistance like in longer wires?

Answer 5

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

Question 6

P6 - Electricity For Gadgets

What is a variable resistor?

Answer 6

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

Question 7

P6 - Electricity For Gadgets

What are variable resistors used for?

Answer 7

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

Question 8

P6 - Electricity For Gadgets

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

Answer 8

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.

Question 9

P6 - Electricity For Gadgets

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

Answer 9

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

Question 10

P6 - Electricity For Gadgets

What is the total resistance in a series circuit?

Answer 10

Sum of individual resistors

Question 11

P6 - Electricity For Gadgets

How is a circuit with resistors in parallel different?

Answer 11

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

Question 12

P6 - Electricity For Gadgets

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

Answer 12

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

Question 13

P6 - Electricity For Gadgets

What is the output of the potential divider?

Answer 13

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

Question 14

P6 - Electricity For Gadgets

How are potential dividers useful?

Answer 14

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

Question 15

P6 - Electricity For Gadgets

What is an LDR?

Answer 15

Light Dependent Resistor - in bright light resistance falls, in darkness resistance is highest. Useful for devices like automatic lights and burglar detectors.

Question 16

P6 - Electricity For Gadgets

What are thermistors?

Answer 16

In hot conditions, resistance drops. In cool conditions, resistance increases. Useful temperature sensors e.g. Car engine temperature gauges and electronic thermostats.

Question 17

P6 - Electricity For Gadgets

How can you make a temperature sensor?

Answer 17

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

Question 18

P6 - Electricity For Gadgets

What is a transistor?

Answer 18

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

Question 19

P6 - Electricity For Gadgets

What are the 3 parts of a transistor?

Answer 19

Base, collector, emitter

Question 20

P6 - Electricity For Gadgets

What does the base do in a transistor?

Answer 20

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.

Question 21

P6 - Electricity For Gadgets

What does the collector do in a transistor?

Answer 21

Current flows into transistor through collector

Question 22

P6 - Electricity For Gadgets

What does the emitter do in a transistor?

Answer 22

Current flows out of transistor through emitter.

Question 23

P6 - Electricity For Gadgets

What is an LED?

Answer 23

A diode that gives out light

Question 24

P6 - Electricity For Gadgets

What does a relay do?

Answer 24

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

Question 25

P6 - Electricity For Gadgets

What is an AND logic gate made from?

Answer 25

2 transistors

Question 26

P6 - Electricity For Gadgets

Why is a relay safer?

Answer 26

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.

Question 27

P6 - Electricity For Gadgets

What is a magnetic field?

Answer 27

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

Question 28

P6 - Electricity For Gadgets

Why is an LED better than an incandescent bulb?

Answer 28

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

Question 29

P6 - Electricity For Gadgets

What is the rule for AND gates?

Answer 29

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.

Question 30

P6 - Electricity For Gadgets

How does a relay work?

Answer 30

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.

Question 31

P6 - Electricity For Gadgets

What is the rule for NOT gates?

Answer 31

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

Question 32

P6 - Electricity For Gadgets

Where is a magnetic field created?

Answer 32

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

Question 33

P6 - Electricity For Gadgets

What is the rule for NAND gates?

Answer 33

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).

Question 34

P6 - Electricity For Gadgets

What is an LED often connected to to protect it?

Answer 34

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

Question 35

P6 - Electricity For Gadgets

What rule is used to work out the magnetic field?

Answer 35

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

Question 36

P6 - Electricity For Gadgets

What is the rule for OR gates?

Answer 36

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.

Question 37

P6 - Electricity For Gadgets

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

Answer 37

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

Question 38

P6 - Electricity For Gadgets

What is the name givento a coil of wire?

Answer 38

Solenoid

Question 39

P6 - Electricity For Gadgets

What is an electromagnet?

Answer 39

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

Question 40

P6 - Electricity For Gadgets

What are the rules for NOR gates?

Answer 40

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)

Question 41

P6 - Electricity For Gadgets

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

Answer 41

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

Question 42

P6 - Electricity For Gadgets

How can the strength of the electromagnet be increased?

Answer 42

By adding more turns to the solenoid.

Question 43

P6 - Electricity For Gadgets

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

Answer 43

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

Question 44

P6 - Electricity For Gadgets

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

Answer 44

It won’t experience any force at all.

Question 45

P6 - Electricity For Gadgets

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

Answer 45

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

Question 46

P6 - Electricity For Gadgets

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

Answer 46

If the current or magnetic field is made stronger.

Question 47

P6 - Electricity For Gadgets

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

Answer 47

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.

Question 48

P6 - Electricity For Gadgets

What does Fleming’s Left Hand Rule tell you?

Answer 48

Which way force acts in a current carrying wire.

Question 49

P6 - Electricity For Gadgets

What 4 factors speed up the simple electric motor?

Answer 49

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

Question 50

P6 - Electricity For Gadgets

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

Answer 50

Direction of field (magnetic)

Question 51

P6 - Electricity For Gadgets

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

Answer 51

Forces act one up and one down - rotates.

Question 52

P6 - Electricity For Gadgets

What is the split-ring commutator?

Answer 52

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

Question 53

P6 - Electricity For Gadgets

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

Answer 53

Direction of current

Question 54

P6 - Electricity For Gadgets

How can the direction of the motor be reversed?

Answer 54

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

Question 55

P6 - Electricity For Gadgets

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

Answer 55

Direction of force (motion)

Question 56

P6 - Electricity For Gadgets

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

Answer 56

Left Hand

Question 57

P6 - Electricity For Gadgets

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

Answer 57

Right hand

Question 58

P6 - Electricity For Gadgets

How are motors made practical?

Answer 58

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.

Question 59

P6 - Electricity For Gadgets

What is electromagnetic induction?

Answer 59

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

Question 60

P6 - Electricity For Gadgets

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

Answer 60

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

Question 61

P6 - Electricity For Gadgets

How can electromagnetic induction be generated?

Answer 61

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.

Question 62

P6 - Electricity For Gadgets

How is AC generated?

Answer 62

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

Question 63

P6 - Electricity For Gadgets

What 4 factors affect the size of the induced voltage?

Answer 63

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

Question 64

P6 - Electricity For Gadgets

How is AC generated by turning a magnet?

Answer 64

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.

Question 65

P6 - Electricity For Gadgets

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

Answer 65

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

Question 66

P6 - Electricity For Gadgets

How does a generator work?

Answer 66

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

Question 67

P6 - Electricity For Gadgets

What do generators have instead of split-ring commutators?

Answer 67

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

Question 68

P6 - Electricity For Gadgets

What current do generators produce?

Answer 68

AC

Question 69

P6 - Electricity For Gadgets

What do faster revolutions produce in a generator?

Answer 69

More peaks and higher overall voltage.

Question 70

P6 - Electricity For Gadgets

What are dynamos?

Answer 70

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

Question 71

P6 - Electricity For Gadgets

How is electricity in a power station generated?

Answer 71

Rotating an electromagnet in a coil of wire.

Question 72

P6 - Electricity For Gadgets

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

Answer 72

Adding more turns to electromagnetic coil.

Question 73

P6 - Electricity For Gadgets

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

Answer 73

By rotating electromagnet coil faster.

Question 74

P6 - Electricity For Gadgets

What are transformers?

Answer 74

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

Question 75

P6 - Electricity For Gadgets

What is a step up transformer?

Answer 75

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

Question 76

P6 - Electricity For Gadgets

What is a step down transformer?

Answer 76

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

Question 77

P6 - Electricity For Gadgets

What is an isolating transformer?

Answer 77

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

Question 78

P6 - Electricity For Gadgets

How does a transformer work?

Answer 78

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.

Question 79

P6 - Electricity For Gadgets

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

Answer 79

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

Question 80

P6 - Electricity For Gadgets

Why doesn’t a transformer work with DC?

Answer 80

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.

Question 81

P6 - Electricity For Gadgets

What do you have to assume with transformers?

Answer 81

It is 100% efficient

Question 82

P6 - Electricity For Gadgets

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

Answer 82

VpIp = VsIs

Question 83

P6 - Electricity For Gadgets

What is the formula for power supplied?

Answer 83

Power = voltage x current P = V x I

Question 84

P6 - Electricity For Gadgets

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

Answer 84

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

Question 85

P6 - Electricity For Gadgets

What is needed to transmit a lot of power?

Answer 85

Either a high voltage or high current

Question 86

P6 - Electricity For Gadgets

What is the problem with a high current?

Answer 86

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

Question 87

P6 - Electricity For Gadgets

What is the formula for power loss?

Answer 87

Power loss = current² x resistance P = I²R

Question 88

P6 - Electricity For Gadgets

What is the significance of the I² in powerloss?

Answer 88

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

Question 89

P6 - Electricity For Gadgets

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

Answer 89

For efficient transmission

Question 90

P6 - Electricity For Gadgets

Where can isolating transformers be used?

Answer 90

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

Question 91

P6 - Electricity For Gadgets

What is the purpose of isolating transformers?

Answer 91

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.

Question 92

P6 - Electricity For Gadgets

What do diodes do?

Answer 92

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)

Question 93

P6 - Electricity For Gadgets

What are diodes made from?

Answer 93

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.

Question 94

P6 - Electricity For Gadgets

What is the n-type semiconductor in a diode?

Answer 94

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

Question 95

P6 - Electricity For Gadgets

What is the p-type semiconductor in a diode?

Answer 95

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.

Question 96

P6 - Electricity For Gadgets

What happens in the diode when there is no voltage?

Answer 96

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

Question 97

P6 - Electricity For Gadgets

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

Answer 97

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.

Question 98

P6 - Electricity For Gadgets

What is half-wave rectification?

Answer 98

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

Question 99

P6 - Electricity For Gadgets

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

Answer 99

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

Question 100

P6 - Electricity For Gadgets

How do you charge a capacitor?

Answer 100

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

Question 101

P6 - Electricity For Gadgets

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

Answer 101

Flow of current decreases.

Question 102

P6 - Electricity For Gadgets

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

Answer 102

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

Question 103

P6 - Electricity For Gadgets

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

Answer 103

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

Question 104

P6 - Electricity For Gadgets

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

Answer 104

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

Question 105

P6 - Electricity For Gadgets

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

Answer 105

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

Question 106

P6 - Electricity For Gadgets

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

Answer 106

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

Question 107

P6 - Electricity For Gadgets

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

Answer 107

Smaller devices can be more expensive - easier to lose.

Question 108

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.

Answer 108

What is current?

Question 109

P6 - Electricity For Gadgets

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

Answer 109

What is voltage?

Question 110

P6 - Electricity For Gadgets

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

Answer 110

What is resistance?

Question 111

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.

Answer 111

What causes resistance?

Question 112

P6 - Electricity For Gadgets

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

Answer 112

What is resistance like in longer wires?

Question 113

P6 - Electricity For Gadgets

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

Answer 113

What is a variable resistor?

Question 114

P6 - Electricity For Gadgets

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

Answer 114

What are variable resistors used for?

Question 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.

Answer 115

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

Question 116

P6 - Electricity For Gadgets

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

Answer 116

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

Question 117

P6 - Electricity For Gadgets

Sum of individual resistors

Answer 117

What is the total resistance in a series circuit?

Question 118

P6 - Electricity For Gadgets

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

Answer 118

How is a circuit with resistors in parallel different?

Question 119

P6 - Electricity For Gadgets

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

Answer 119

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

Question 120

P6 - Electricity For Gadgets

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

Answer 120

What is the output of the potential divider?

Question 121

P6 - Electricity For Gadgets

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

Answer 121

How are potential dividers useful?

Question 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.

Answer 122

What is an LDR?

Question 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.

Answer 123

What are thermistors?

Question 124

P6 - Electricity For Gadgets

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

Answer 124

How can you make a temperature sensor?

Question 125

P6 - Electricity For Gadgets

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

Answer 125

What is a transistor?

Question 126

P6 - Electricity For Gadgets

Base, collector, emitter

Answer 126

What are the 3 parts of a transistor?

Question 127

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.

Answer 127

What does the base do in a transistor?

Question 128

P6 - Electricity For Gadgets

Current flows into transistor through collector

Answer 128

What does the collector do in a transistor?

Question 129

P6 - Electricity For Gadgets

Current flows out of transistor through emitter.

Answer 129

What does the emitter do in a transistor?

Question 130

P6 - Electricity For Gadgets

A diode that gives out light

Answer 130

What is an LED?

Question 131

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.

Answer 131

What does a relay do?

Question 132

P6 - Electricity For Gadgets

2 transistors

Answer 132

What is an AND logic gate made from?

Question 133

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.

Answer 133

Why is a relay safer?

Question 134

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.

Answer 134

What is a magnetic field?

Question 135

P6 - Electricity For Gadgets

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

Answer 135

Why is an LED better than an incandescent bulb?

Question 136

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.

Answer 136

What is the rule for AND gates?

Question 137

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.

Answer 137

How does a relay work?

Question 138

P6 - Electricity For Gadgets

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

Answer 138

What is the rule for NOT gates?

Question 139

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.

Answer 139

Where is a magnetic field created?

Question 140

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).

Answer 140

What is the rule for NAND gates?

Question 141

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.

Answer 141

What is an LED often connected to to protect it?

Question 142

P6 - Electricity For Gadgets

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

Answer 142

What rule is used to work out the magnetic field?

Question 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.

Answer 143

What is the rule for OR gates?

Question 144

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.

Answer 144

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

Question 145

P6 - Electricity For Gadgets

Solenoid

Answer 145

What is the name givento a coil of wire?

Question 146

P6 - Electricity For Gadgets

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

Answer 146

What is an electromagnet?

Question 147

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)

Answer 147

What are the rules for NOR gates?

Question 148

P6 - Electricity For Gadgets

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

Answer 148

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

Question 149

P6 - Electricity For Gadgets

By adding more turns to the solenoid.

Answer 149

How can the strength of the electromagnet be increased?

Question 150

P6 - Electricity For Gadgets

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

Answer 150

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

Question 151

P6 - Electricity For Gadgets

It won’t experience any force at all.

Answer 151

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

Question 152

P6 - Electricity For Gadgets

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

Answer 152

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

Question 153

P6 - Electricity For Gadgets

If the current or magnetic field is made stronger.

Answer 153

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

Question 154

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.

Answer 154

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

Question 155

P6 - Electricity For Gadgets

Which way force acts in a current carrying wire.

Answer 155

What does Fleming’s Left Hand Rule tell you?

Question 156

P6 - Electricity For Gadgets

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

Answer 156

What 4 factors speed up the simple electric motor?

Question 157

P6 - Electricity For Gadgets

Direction of field (magnetic)

Answer 157

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

Question 158

P6 - Electricity For Gadgets

Forces act one up and one down - rotates.

Answer 158

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

Question 159

P6 - Electricity For Gadgets

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

Answer 159

What is the split-ring commutator?

Question 160

P6 - Electricity For Gadgets

Direction of current

Answer 160

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

Question 161

P6 - Electricity For Gadgets

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

Answer 161

How can the direction of the motor be reversed?

Question 162

P6 - Electricity For Gadgets

Direction of force (motion)

Answer 162

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

Question 163

P6 - Electricity For Gadgets

Left Hand

Answer 163

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

Question 164

P6 - Electricity For Gadgets

Right hand

Answer 164

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

Question 165

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.

Answer 165

How are motors made practical?

Question 166

P6 - Electricity For Gadgets

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

Answer 166

What is electromagnetic induction?

Question 167

P6 - Electricity For Gadgets

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

Answer 167

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

Question 168

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.

Answer 168

How can electromagnetic induction be generated?

Question 169

P6 - Electricity For Gadgets

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

Answer 169

How is AC generated?

Question 170

P6 - Electricity For Gadgets

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

Answer 170

What 4 factors affect the size of the induced voltage?

Question 171

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.

Answer 171

How is AC generated by turning a magnet?

Question 172

P6 - Electricity For Gadgets

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

Answer 172

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

Question 173

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.

Answer 173

How does a generator work?

Question 174

P6 - Electricity For Gadgets

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

Answer 174

What do generators have instead of split-ring commutators?

Question 175

P6 - Electricity For Gadgets

AC

Answer 175

What current do generators produce?

Question 176

P6 - Electricity For Gadgets

More peaks and higher overall voltage.

Answer 176

What do faster revolutions produce in a generator?

Question 177

P6 - Electricity For Gadgets

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

Answer 177

What are dynamos?

Question 178

P6 - Electricity For Gadgets

Rotating an electromagnet in a coil of wire.

Answer 178

How is electricity in a power station generated?

Question 179

P6 - Electricity For Gadgets

Adding more turns to electromagnetic coil.

Answer 179

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

Question 180

P6 - Electricity For Gadgets

By rotating electromagnet coil faster.

Answer 180

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

Question 181

P6 - Electricity For Gadgets

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

Answer 181

What are transformers?

Question 182

P6 - Electricity For Gadgets

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

Answer 182

What is a step up transformer?

Question 183

P6 - Electricity For Gadgets

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

Answer 183

What is a step down transformer?

Question 184

P6 - Electricity For Gadgets

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

Answer 184

What is an isolating transformer?

Question 185

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.

Answer 185

How does a transformer work?

Question 186

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.

Answer 186

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

Question 187

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.

Answer 187

Why doesn’t a transformer work with DC?

Question 188

P6 - Electricity For Gadgets

It is 100% efficient

Answer 188

What do you have to assume with transformers?

Question 189

P6 - Electricity For Gadgets

VpIp = VsIs

Answer 189

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

Question 190

P6 - Electricity For Gadgets

Power = voltage x current P = V x I

Answer 190

What is the formula for power supplied?

Question 191

P6 - Electricity For Gadgets

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

Answer 191

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

Question 192

P6 - Electricity For Gadgets

Either a high voltage or high current

Answer 192

What is needed to transmit a lot of power?

Question 193

P6 - Electricity For Gadgets

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

Answer 193

What is the problem with a high current?

Question 194

P6 - Electricity For Gadgets

Power loss = current² x resistance P = I²R

Answer 194

What is the formula for power loss?

Question 195

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.

Answer 195

What is the significance of the I² in powerloss?

Question 196

P6 - Electricity For Gadgets

For efficient transmission

Answer 196

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

Question 197

P6 - Electricity For Gadgets

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

Answer 197

Where can isolating transformers be used?

Question 198

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.

Answer 198

What is the purpose of isolating transformers?

Question 199

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)

Answer 199

What do diodes do?

Question 200

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.

Answer 200

What are diodes made from?

Question 201

P6 - Electricity For Gadgets

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

Answer 201

What is the n-type semiconductor in a diode?

Question 202

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.

Answer 202

What is the p-type semiconductor in a diode?

Question 203

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.

Answer 203

What happens in the diode when there is no voltage?

Question 204

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.

Answer 204

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

Question 205

P6 - Electricity For Gadgets

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

Answer 205

What is half-wave rectification?

Question 206

P6 - Electricity For Gadgets

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

Answer 206

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

Question 207

P6 - Electricity For Gadgets

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

Answer 207

How do you charge a capacitor?

Question 208

P6 - Electricity For Gadgets

Flow of current decreases.

Answer 208

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

Question 209

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.

Answer 209

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

Question 210

P6 - Electricity For Gadgets

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

Answer 210

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

Question 211

P6 - Electricity For Gadgets

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

Answer 211

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

Question 212

P6 - Electricity For Gadgets

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

Answer 212

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

Question 213

P6 - Electricity For Gadgets

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

Answer 213

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

Question 214

P6 - Electricity For Gadgets

Smaller devices can be more expensive - easier to lose.

Answer 214

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