2 - electricity Flashcards
1
Q
what is the relationship between power, current, and voltage?
A
P=IV
2
Q
what is the relationship between energy transferred, current, voltage, time
A
E =I x t x V
3
Q
what is current?
A
the rate of flow of charge around the circuit
4
Q
what carries charge?
A
electrons - they are negatively charged particles
in solid metal conductors!
5
Q
when will current flow?
A
current will only flow when there is a voltage across the component
6
Q
what is the unit for current?
A
ampere (amps) , A
7
Q
what is another name for voltage?
A
potential difference
8
Q
what does resistance do
A
slows the flow down
9
Q
what is voltage measured in
A
volts, V
10
Q
what can resistance be?
A
anything that slows the flow down. If you add more components to a circuit, there will be a higher overall resistance
11
Q
what is the unit for resistance?
A
ohms, Ω
12
Q
what happens if you increase the voltage?
A
more current will flow
13
Q
what happens if you increase resistance?
A
less current will flow. more voltage is needed to keep the same current flowing
14
Q
what does an ammeter do?
A
measure current flowing through the component. they must be placed in series, never in parallel
15
Q
what does a voltmeter do?
A
measures the voltage across the component. must be placed in parallel around the component under test - NOT around the variable resister of battery
16
Q
draw a variable resistor.
A
17
Q
what does a variable resistor do?
A
A variable resistor is an electronic component that changes the resistance in a circuit, which in turn controls the flow of current
18
Q
what is mains supply?
A
A.C
19
Q
what is battery supply?
A
D.C
20
Q
what is the Uk mains supply in volts?
A
around 230 volts
21
Q
what does a.c mean?
A
current is constantly changing direction whereas in dc it keeps flowing in the same direciton
22
Q
what does an I-V graph show?
A
how current varies as you change voltage
23
Q
what does the i-v graph of a wire look like?
A
the current through a wire is proportional to temperature at constant temp. it is a straight line crossing through 0,0
24
Q
what does the i-v graph of a metal filament lamp look like?
A
as the temperature of the metal filament increases, the resistance increases, hence it is a curve. the line is shaped like a very light s of fancy f w/o the line through (ƒ this vibe but more diagonal)
25
what does the i-v graph of different resistors look like?
the current through a resistor at constant temp is proportional to voltage. diff resisters have different voltages so they will have different slopes, however all will be a straight line (goin in diagonal direction)
26
what does the i-v graph of a diode look like?
current will only flow through a diode in one direction, so its flat until voltage it positive and it goes like basically straight up (like the right half of a U)
27
draw the symbol of a cell
28
draw a battery
multiple cells
29
draw the different symbols for the power supply
check p.18 of CGP books
30
draw what a switch open/closed looks like
31
what does an earth/ground look like?
32
draw a fuse/circuit brekaer
33
draw a transformer
34
draw a filament lamp
35
draw an LED
36
draw a loudspeaker
37
draw a microphone
38
draw an electric bell
39
draw a motor
40
draw a heater
41
draw a generator
42
draw a fixed resistor
43
draw a variable resistor
44
draw an ammeter
45
draw a voltmeter
46
draw a diode
47
draw an LDR
48
draw a thermistor
49
draw a relay
50
what can LED lamps indicate?
that current is present in a circuit
51
what is an LDR? what is a use?
A dependant resistor is a special type of resistor that changes its resistance depending on how much light falls on it. in bright light, the resistance falls and in darkness, the resistance is highest.
this makes it a useful device for electronic circuits like burglar detectors
52
what is a thermistor? what is a use?
a temperature-dependent resistor. in hot conditions, the resistance drops, and in cool conditions, the resistance goes up.
this makes them useful in temperature detectors like in a car engine, temperature sensors, thermostats, and fire alarms
53
what is the relationship between voltage, current, resistance
v = ir
54
what is the relationship between charge, current, time?
Q = I x t
55
what is the symbol for charge?
Q
56
what is voltage?
the energy transferred per unit charge passed
57
what a volt also = to?
volt = joules per coulomb
58
what is the relationship between energy transferred, charge, and voltage?
energy transferred = charge x voltage
E = Q x V
59
what happens to voltage in a series circuit?
it is split (shared among all components)
60
what happens to current in a series circuit?
current is constant in all parts (stays the same)
61
what happens to voltage in a parallel circuit?
the voltage stays the same in all branches
62
what happens to resistance in a series circuit?
total resistance is the sum of all resistance in components. this depends on the number of components and the type of components used
63
what happens to current in a parallel circuit?
current is split (between the branches based on resistance)
64
what can series circuits be used for?
fairy lights
65
what does the potential difference in each component depend on in a series circuit?
resistance
66
what can parallel circuits be used for?
household electrics, cars, lights in your house
67
why are parallel circuits better than series circuits?
if one component breaks, then it still works
68
what does the current in a branch depend on?
depends on the resistance of the branch - the higher it is, the harder it is for charge to flow, so current is lower. the total resistance of the circuit decreases if you add a second resistor in parallel
69
if the current is large, what is the current?
also large
70
what is charge measured in?
coulombs (C)
71
what is charge?
charge is a property of matter that describes how many more or fewer electrons an object has than protons
72
what happens when an electrical charge goes through a change in voltage?
energy (E) is transferred
73
why is current conserved at a junction in a circuit?
This is because no charge is gained or lost. idk its on the checklist and google isn't helping
74
what happens when current passes through resistors? why?
they get hot. this is because there is an energy transfer that heats the resistor. this happens when electrons collide with ions in the lattice that make up the resistor as they flow through it. this gives the ions energy, which causes them to vibrate and heat up.
75
what happens to a resistor when it is heated?
its resistance increases, so less current will flow, or a greater voltage will be needed to produce the same current.
this can also cause components in the circuit to melt, meaning the circuit will stop working properly.
76
what do fuses do?
protect circuits as they melt and break the circuit if the current gets too high
77
what are some positives of the heating effect?
you can heat things e.g., toasters use this (they contain a coil of wire with really high resistance, so when current passes though, temperature increases so much that it glows and gives off infrared (heat) radiation which cooks the bread
78
how does current vary in metal filament lamps
In a metal filament lamp, the current increases more slowly than the potential difference because the filament's resistance increases as the filament heats up
79
how does current vary in a diode?
The current that varies in a diode depends on the voltage applied across it, and whether the diode is forward-biased or reverse-biased:
80
what are some hazards and controls that you need to keep when measuring how current is affected
Hazards and control measures
Hazards
Heating of the resistance wire
Consequence
Burns to the skin
Control measures
Do not touch the resistance wire whilst the circuits are connected and allow it time to cool
81
how would you investigate the effect of a diode on current?
Method
Connect the circuit as shown in the diagram having chosen a suitable protective resistor (between 100 Ω and 500 Ω).
Set the variable resistor to give the lowest potential difference and record the readings on the voltmeter and milliammeter.
Alter the variable resistor to increase the potential difference by 0.2 V.
Record the new readings on the voltmeter and milliammeter.
Repeat steps three to four, each time increasing the current slightly.
Reverse the power supply connections and repeat steps two to six.
Plot a graph of current against potential difference for the diode.
(V=IR)
82
how would you investigate the effect of a resistor on current? or filament lamp
Method
Connect the circuit as shown in the first diagram.
Ensure that the power supply is set to zero at the start.
Record the reading on the voltmeter and ammeter
Use the variable resistor to alter the potential difference.
Record the new readings on the voltmeter and ammeter.
Repeat steps three to four, each time increasing the potential difference slightly.
Reverse the power supply connections and repeat steps two to six.
Plot a graph of current against potential difference for each
component
Repeat the experiment but replace the
fixed resistor with a bulb.
do the same with a filament lamp
83
how would you investigate the effect of a filament lamp on current?
Method for Filament Lamp
Set up a circuit. Set up a circuit with a cell, an ammeter, variable resistor and a filament lamp in series. Attach a voltmeter in parallel across the filament lamp. In the experiment, we need to ensure that the temperature stays constant.
Alter the current. Change the current in the circuit by moving the variable resistor. This will change the resistance in the circuit, therefore altering the current flow through the filament lamp.
Record values for current and voltage for a given resistance. For a given resistance, record a value for the current (from the ammeter) and the potential difference (from the voltmeter), in the results table below.
Repeat step 3 two more times. Repeat step 3 twice. You should keep the same resistance, so the current stays the same, but you might get slightly different values for potential difference. After, find an average pd for each value of current. This step improves reliability.
84
what do like charges do? what do opposite charges do?
like charges repel, opposite charges attract (there are forces of attraction between unlike charges)
85
when do forces get weaker?
the further away you are
86
what conducts charge? what doesn't?
conductors conduct charge, insulators don't
87
what is a static charge?
a static charge is a charge which builds up in one place and is not free to move.
88
where is static charge more common?
on insulators, where current cannot flow
89
what is a common cause of static electricity? what happens when this happens?
friction. when two insulating materials are rubbed together, electrons will be scraped off on and dumped on the other. they will leave a positive electrostatic charge on one and a negative electrostatic charge on the other.
which way the electrons transfer depends on the material
90
what are positive and negative electrostatic charges produced by?
the movement of electrons
91
name an example of when electrostatic charges have affected conductors.
cars often get a static charge on the outside because they've gained or lost electrons from air rushing past them as they travel at high speeds
92
how can a charged conductor be discharged safely?
by connecting it to earth with a metal strap so that the electrons can flow down the strap to the ground it the charge is negative and flow up the strap from the ground if the charge is positive
93
what happens when electrical charge on an isolated object builds up?
the voltage between the object and earth increases. if the voltage becomes large enough, the electrons can jump across the gap between the charged object and the earth aka a spark. they can also jump to any earthed conductor that is nearby which is why you can get static shocks from clothes or getting out a car
94
what are common electrical conductors?
metals like silver, copper, aluminium, steel, brass
95
what are common insulators?
plastic as well as wood, glass, and rubber
96
suggest why the wires in the clothes iron cable are thicker than the wires in
the lamp cable.
higher current, lower resistancw
97
Suggest why the lamp is safe to use, even though its cable only has two wires.
double insulated
does not have a metal case / has a
plastic case
98
what is a variable resistor? why use it?
an electronic component that allows you to change the resistance in an electric circuit to control the flow of current.
you woudl use it to control the flow of current
99
if a quastion asks you to comment on a graph, what are 2 things you can automatically comment on?
whether or not the graph is proportional/inversly proportional, and whether the relaitonship is linear or non- linear (like a straight line or not)
100
The resistance of the filament lamp changes as the voltage is increased.
(i) How can you tell this from the graph? (or V-I with filament lamp)
idea that gradient changes;
e.g.
voltage increases more rapidly than the current
101
The resistance of the filament lamp changes as the voltage is increased.
(ii) Explain these changes in resistance.
MP1. Lamp heats up;
MP2. Greater chance of electron collisions;
MP3. (hence) resistance increases;
102
