Paper 2-SP10,SP11 Flashcards
(128 cards)
1
Q
What metal is used for electrical wiring?
A
Copper.
2
Q
What do metal wires need?
A
Free electrons.
3
Q
What happens when a battery is attacked to the wire?
A
The voltage ‘pushes’ the free electrons around the circuit. The electrons are negative so they move towards the positive terminal of the battery.
4
Q
What is the conventional current?
A
Positive to negative.
5
Q
Show the difference between the conventional direction of current flow and the direction of electron flow?
A
6
Q
What is the symbol and component for a switch(open)?
A
7
Q
What is the symbol and component for a cell?
A
8
Q
What are the symbol and component for a battery?
A
9
Q
What are the symbol and component for a lamp?
A
10
Q
What are the symbol and component for an ammeter?
A
11
Q
What is the symbol and component for a voltmeter?
A
12
Q
What are the two types of circuits?
A
Series and parallel.
13
Q
What is a series circuit?
A
There is just one route the current can take around the circuit.
14
Q
What is a parallel circuit?
A
There are are junctions that allow the current to take different routes.
15
Q
How do lamps work in series circuits as compared to parallel?
A
Lamps cannot be switched on and off individually, and if one lamp fails, they will all switch off whereas in parallel circuits they can be switched separately.
16
Q
What is electrical current measured in?
A
Amperes(Amps)(A).
17
Q
What is electrical current measured with?
A
An ammeter.
18
Q
Is current conserved?
A
Yes and the current leaving the positive terminal of the battery is the same as the current arriving at the negative terminal. Total current entering junction same as leaving.
19
Q
What do you need to push current around an electrical circuit?
A
A potential difference.
20
Q
What is potential difference also called?
A
Voltage.
21
Q
What also must happen for a current to flow?
A
The circuit must be closed and contain a source of potential difference such as a cell or battery. The elctrons will then all move together.
22
Q
What is the potential difference like across each of the branches in a parallel circuit?
A
It is always the same, when there is more than one component in a branch of a circuit, the potential differences across all components add up.
23
Q
What is potential difference measured in?
A
Volts.
24
Q
What is potential difference measured with?
A
A voltmeter,
25
Where does the electric current flow from?
Negative to positive.
26
Is energy conserved in a current?
No.
27
What is conventional current?
Pos to neg and we draw it like that as scientists used to be dumb.
28
What happens to energy in electrical circuits?
It is transferred.
29
What happens to the voltage in series circuits?
It is split.
30
What happens to potential differences on parallel circuits?
For components connected in parallel, the potential differences is the same.
31
Look at this.
32
What do all the cells in a battery have to be?
Pointing in the same direction or the PT will be 0, well if there is more it just cancels out so like yh watch "potential difference from batteries" by free science lessons.
33
What is the equation for charge flow?
Current x time
34
What is charge flow measured in?
C(coulombs)
35
What is the equation for energy transferred?
Charge flow x potential difference.
36
What is resistance measured in?
Ohms (omega symbol)
37
What is the equation for potential difference?
Current x resistance
38
What do resistors do in series?
Total resistance is increased because pathway becomes harder, PD is shared between resistors but may not be equal. Greater PD across resistors with higher resistances.
39
What do resistors do in parallel circuits?
Total resistance is less the resistance of individual resistors because there are more paths for the current.
40
Show the graph of current with different things.
41
What happens to filament lamps as the potential difference increases?
Hotter and brighter but the resistance increases so they are not in proportion.
42
How does the resistance of diodes change?
Low resistance if PD is in one direction but high PD is in the opposite direction so current can only flow in one direction.
43
What is an LDR?
Light-dependant resistor has a high resistance in the dark but the resistance gets smaller when the light intensity increases.
44
What is the resistance of thermistors like?
High resistance at low temperatures but as the temperature increases the resistance decreases.
45
What is resistance?
The PD required to drive a current through a component.
46
Why is resistance not bad?
Sometimes we want to add it through a resistor.
47
What is the symbol for a resistor?
Hollow rectangle.
48
What is the current through a resistor?
Directly proportional to the potential difference. Resistors like these are called These are called ohmic conductors but this only applies if the temp does not change.
49
What is the graph for current and PD like for an ohmic conductor?
Constant.
50
What does the word filament mean?
A very fine wire.
51
What is the graph for a filament lamp like for PD and current?
Not directly proportional as the filament gets hot so the resistance increases.
52
What happens to the filament when it is hot?
The atoms vibrate more so the electrons in the current now collide more with the atoms.
53
Is a filament lamp an ohmic conductor?
No.
54
What does LED stand for?
Light emitting diode.
55
What is the symbol for a diode?
56
What is the key feature of a diode?
The current flows in one direction only.
57
Why does the current in a diode only flow in one direction?
Because diodes have a very high resistance in the reverse direction.
58
What does the arrow on a diode show?
Direction the conventional current is flowing.
59
What are diodes extremely useful for?
Controlling the flow of current in circuits.
60
What is the symbol for an LED?
61
What does an LED do when a current flows through it?
It gives off light.
62
Are LED's an efficient source of light?
Yes.
63
What happens to resistors in series?
They add together.
64
What is it called when, 20r + 40r or 60r?
Equivalent resistamce.
65
What happens to resistors in parallel?
The total resistance of two resistors in parallel is less than the resistance of the smallest individual resistor.
66
What is the symbol for an LDR?
67
What happens to the resistance of LDR's in dark conditions?
It has a high resistance, it is low in the light.
68
What is one use of an LDR?
When you put your phone to your ear to talk on it the light turns off to save battery.
69
What is the symbol for a thermistor?
70
What are thermistors?
The resistnace of a thermistor decreases if the temperature increases.
71
What are thermistors useful as?
Thermostats and fire alarms
72
What is work done against in a circuit?
The resistance. The energy is transferred by heating and the resistor gets warm.
73
How do resistors work?
74
How can resistance be reduced?
Using wires made from metals with lower resistance like copper, or using thicker wires. You can cool metals so the lattice ions dont vibrate as much.
75
What is the equation for energy transferred?
Current x PD x time
76
What is the equation for power?
Energy transferred/time
77
What is the units for power?
Watts (joules per second)
78
What is the equation for electrical power?
Electrical power=current x PD
79
What is another equation for electrical power?
Electrical power= current squared x resistance.
80
What do appliances that need large amounts of power use?
The mains electricity.
81
How is electricity carried to our homes?
Network of wires and cables known as the national grid.
82
What is the UK mains voltage?
230V
83
What shows the power?
Power rating.
84
What are the two types of supply?
A.C and D.C
85
DC?
Direct current.
86
AC?
Alternating current.
87
What is the current from a cell?
Only moves in one direction so is a direct current.
88
What is mains electricity?
Alternating current.
89
What is alternating current?
Current is constantly changing direction.
90
What is the benefit of alternating current?
it is very easy to use a transformer to increase or decrease the potential difference.
91
What is the frequency of UK main AC?
50hz so switches between direction 50 times a second. It has to go back tho so like not just there.
92
What is used to see the pattern of an electrical current?
An oscilloscope.
93
Does the PD change with DC?
No.
94
Does the PD change with AC?
Yes.
95
What cable does the mains use?
3 core cable.
96
What are the wires made of?
Copper as it is a good conductor of electricity.
97
What are the coatings of the wire made of?
Plastic as it does not conduct electricity.
98
What is the brown wire?
Live wire- carries the alternating PD from the supply.
99
What is the brown wire connected to?
A fuse in the plug.
100
What is the blue wire?
Neutral wire-completes the circuit, potential difference = 0v compared to the brown wire.
101
What is the green and yellow striped wire?
Earth wire- this is a safety wire to stop the appliance from becoming live.
102
What wire is dangerous?
The live wire and it could be fatal if it is touched.
103
Why can appliances with a metal case be dangerous?
If the live wire comes loose and touches the metal case the case can become live.
104
What is done to make sure the metal casing is not dangerous?
The metal case is attached to the earth wire and the earth wire is connected to the ground with a metal rod so if the case becomes live the huge current will go to the earth, the fuse melts and shuts off the current.
105
What is the fuse?
A safety device marked with the current it can carry, 3,5 or 13A. It is a tube with a thin wire inside and the current passes through the wire and the wire gets hotter, if the currents exceeds a certain value the wire melts and the circuit is broken so the current stops.
106
How is a switch used as a safety feature?
Switches are connected in the live wire, when they are off, no current goes through the appliance.
107
How does a fuse stop fires?
If a faulty appliance draws too much current it can overheat. a fuse stops fires.
108
What is an alternative to fuses?
Cicrcuit breakers, they detect a change in the current and safely switch off the supply.
109
What is an advantage of circuit breakers?
Once a fault is fixed they can be switched back on again, whereas a fuse has to be replaced. Another advantage of some types is that they work very quickly so can save lives. A fuse takes time to melt and will not prevent you getting a shock.
110
What is the national grid a system of?
Transformers and high-voltage cables.
111
What is the problem with getting electricity to homes?
Energy is always lost in the power cables due to the resistance of the wires.
112
How can we reduce the energy loss when getting energy to homes?
We can build the power statins near to homes. Or we can use transformers.
113
What materials can collect charge?
Insulates as the charges cannot flow through them.
114
Why does hair stick up?
Charge cant flow to surroundings so they repel each other.
115
What can a build up of static electricity cause?
A spark.
116
When can a spark be dangerous?
It can build up as the fuel flows through the refuelling pipe. This could cause a spark and trigger an explosion.
117
How are planes kept safe when refuelling?
Both the refuelling truck and the aeroplane are earthed. This prevents any charges building up.
118
Explain charging by induction?
119
What causes lightning?
Static electricity builds up due to friction between particles of ice or water moved by air currents, when the charge is large enough, charged particles travel through the air and causes thunder and lighting. Lightning can be dangerous so buildings are earthed with lightning conductors made of thick metal running down from the top to the earth.
120
What happens with static electricity at petrol filling stations?
121
Explain electrostatic spray?
122
What is a force field?
The volume of space around an object in which another object can experience a force. A magnet has a force field around it called a magnetic field. A magnetic material will feel a force from the magnet if it is inside this magnetic field.
123
What does a charged object have?
A force field around it called an electric field (electrostatic field)
124
What is a single point with charge?
A point charge.
125
What are the lines around a point charge called?
Field lines.
126
What are the rules with field lines?
they never cross, show where it is strongest as they are closer together, start on positive and end on neg.
127
What is the electric field between two parallel plates?
Uniform so it is same in all places.
128
Frequency of mains AC?
50HZ BACK AND FORTH 50 TIMES
