1
Q
what are the two types of electric charge
A
positive and negative
2
Q
what do like charges do
A
they repel
3
Q
what do opposite charges do
A
they attract
4
Q
what makes up a nucleous
A
protons and nuterons
5
Q
protons?
A
positive
6
Q
nutrons
A
nuetral
7
Q
electrons
A
- negative,
- orbit the atom,
- move when electricity flows
8
Q
conductors
A
have many free electrons so move easily allowing electricity to flow through it
9
Q
examples of conductors
A
gold,iorn,steel,copper
10
Q
insulators
A
have few electrons so cannot move easily electricty struggles to flow through it
11
Q
examples of insulators
A
plastic,rubber,wood
12
Q
electrical current
A
rate of flow of charge. 1 ampre is equal to 1 coulomb of charge flowing past a point in 1 second
13
Q
equation for charge
A
Q=It
Q=charge,coloubs(C)
I=current,ampres(A)
t-time(s)
14
Q
what happens when an object gains electrons
A
it becomes negativly charged
15
Q
what happens when an object loses electrons
A
it becomes positively charged
16
Q
electric fields
A
reigion surrounding a charged object where another charged object experiences a force.
can make particle move which depends on the the electric field
17
Q
what do electric fields lines do
A
- never touch or cross
- closer the lines stronger the field
- greater distance away the weaker
18
Q
positive field
A
lines move away
19
Q
negative field
A
move towards
20
Q
potential difference
A
measure of the difference in energy per coulomb of charge at two points in a circut
21
Q
what is the meaure between the two termials of a battery
A
electrical energy given to the eletrical circut by the battery
22
Q
can voltage and potential difference be used intergangeably
A
yes
23
Q
what does a.c stand for
A
alternating current
24
Q
what is ac
A
- flow of electrons
- regularly changes direction.
- voltage varies from 0 to peak in one direction back to 0, peak in other direction
25
what does d.c stand for
direct current
26
what is d.c
flow of electrons in one direction
voltage remains constant
27
d.c reversed
means volatge flows other direction
28
series circuts
* only has one direction
* current is same at all points
* sum of voltage across all compoments is equal to the voltage of the supply
29
parallel circuts
* has more than one path for the current
* sum of current across all branches is equal to the current drawn from the supply
* voltage is the same at all points
30
measuring current
measures eletric current
measured in ampres (A)
ammeter measures the current in a componment
31
measuring voltage
measures potential difference/voltage
measured in volts(V)
voltmeter measures the voltage across componements
32
resistance def
opposition to the flow of current
33
resistance
* better the conductor the lower the resistance
* higher the resistance the lower the current
* resistance is measured in ohms(Ω)
34
resistance in series
Rtotal=R1+R2
35
resistance in parallel
1/RT=1/R1+1/R2
36
Ohms law
explains the relationship between voltage and current. that is directly proportional
37
equation for ohms law
V=IxR
38
Experiment for ohms law
Set up circut
-vary the potential difference across the resistor by turning the control on the power supply
-record the current in the resistor at different potential differences(voltages)
39
Analysis of ohm's law experiment
voltage and current are directly proportional
gradient of V-I graph gives us the value of resistance
40
ohmic conductors
componment that obeys ohms law
41
non-ohmic conductors
does not obey ohms law on graph does not follow a straight line but curved showing resistance increases as current increases
42
cell
provides electrical energy to charges in a circut
43
battery
provides electrical energy to charges in a circut
more than one cell connected in series
44
lamp
produces light energy when a current flows through it
45
switch
used to control current in a circut by making a break
46
fixed resister
control level of current, cannot change level
47
motor
turns on when current flows through it
electrical energy to kinetic energy
48
microphone
converts sound energy to electrical energy
49
photo voltaic cell
creates voltage with light
light energy to eletrical energy
50
fuse (short)
contains thin bit of wire that melts/breaks if current to high
51
capacitor (short)
can be used to store eletric charge
52
relay (short)
switch that colses when eletrical energy passes through coil
eletrical to kinetic energy
53
varible resistor
control level of current. can be changed
54
LDR
light dependent resistor. resistance changes depending on light level present. LURD - light up, resistance down
55
Thermistor
reistance changes depending on temperture
TURD, temperture up, resistance down
56
diode
allows current to flow in one direction only
57
LED
light emmiting diode
produces light energy when a current flows through it but only in one direction
58
NPN transistor
used as switch. on when input voltage is greater than or equal to 0.7V
59
Mosfet transistor
used as switch. on when input voltage is greater than or equal to 2V
60
photo-voltic cell (long)
often called a solar cell
converts solar energy to electrical energy
61
diode(long)
allows current to flow in only one direction
should be pointing towards the smaller/negative side of power supply
62
LED (long)
* Light emmiting diode
* emmits light
* destroyed by high currents
* needs a resistor in series so can reduce current
63
working out size of resistor for LED
supply voltage- max voltage
use ohms law V=IR
64
capacitor(long)
* two metal plates seperated by an insulator
* stores electric charge
* discharged capacitor has no voltage across its plates
* when charging up voltage takes time to reise to supply voltage
* when fully charged equal to the supply
65
what impacts the time taken for a capacitor to fully charge
size of capacitor
value of charging current
66
thermistor (long)
resistance depends on it temperture
TURD- temperture up, resistance down
67
things that may have a thermistor
oven, fridge, green house
68
LDR (long)
light dependent resistor. resistance changes depending on light level present. LURD - light up, resistance down
69
thing that may have an LDR
Lampposts
70
relay (long)
switch that is operated by a magnetic field.
use low current circut to control high level circut
71
Potential dividers
* pair of resistors that can be used to divide up the voltage from a supply
* means can get exactly the voltage needed
* voltage across resistor is releated to its reistance
* higher the resistance of a resistor high voltage across it
* current passing through both resistors is the same
72
equations for potenital dividers
R1/R2=v1/v2
v2=(r2/r1+r2) vs
Rt=R1+R2
Vs=Ix Rt
V1=IxR1
73
transistor
often used in switching circuts like a switch
74
NPN transistor (long)
* if high enough voltage applied to base current flows between collector and emmitor
* switch on 0.2V
75
Mosfets (long)
* Metel Oxide Semi-conductor field effect tranistors
* can handle bigger output than NPN
* switch on about 2V
* can be used in bulb/motors
76
Power & equation
measure of the rate at which energy is transferred
P=E/T
77
Electrical power & equation
rate at which electrical energy is transferred
depends on current and voltage
P=Iv
78
Alternate power formulas
P=I²R
P=v²/r
79
fuses (long)
* if device draws too high current thin bit of metal breaks and cuts off current
* stops from overheating and causing a fire
* different ratings for size of current
80
two common fuse ratings
3A and 13A
81
fuse rule
power rating less than 720W use 3A fuse
and above use 13A
82
how to work out which fuse to use
P=IV if between 3-13 use 13A
Physcis N5
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