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Physics > Electricity 1 > Flashcards

Electricity 1 Flashcards

(80 cards)

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1
Q

when is an object neutral

A

when it has the same number of protons as electrons

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2
Q

positive charge

A

more protons than electrons

loss of electrons

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3
Q

negative charge

A

more electrons than protons

gain of electrons

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4
Q

like charges

A

repel

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5
Q

opposite charges

A

attract

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6
Q

charge resides…

A

… on the outer surface of the object

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7
Q

measurement of surface charge density

A

charge per m squared

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8
Q

surface charge density is greatest at

A

sharp corners of the object

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9
Q

3 uses of outer surface charge distribution

A
  1. coaxial cable
  2. electrostatic shielding
  3. faraday cage
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10
Q

what happens to air molecules near a sharp charged object

A

they are ionised, split into positive and negative ions

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11
Q

definition of electric field

A

the region around a charged object in which its electric forces act

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12
Q

electric field lines radiating from the charge

A

radial field

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13
Q

electric field lines travel from positively charged plate to negatively charged plate

A

uniform field

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14
Q

electric field lines travel from positive charge to negative charge

A

opposite charges

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15
Q

2 properties of electric field lines

A
  1. there are no electric field lines inside an electric charged conductor
  2. a metal like aluminium can be used to alter an electric field
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16
Q

what is the basis for electrostatic shielding

A

a metal like aluminium can be used to alter an electric field

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17
Q

basis of the faraday cage

A

there is no electric field inside a hollow charged conductor

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18
Q

electric field in an airplane

A

an aircraft in flight may become charged due to friction between the air and the body of the aircraft. This build up of charge could lead to sparks when the aircraft lands and is being refuelled. Tyres made of conducting materials are used to remove the charge from the body of the aircraft upon landing

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19
Q

electrostatic precipitator

A

used to remove dust particles from the chimney of a power station. The dust particles become charged as they pass through a charged wire grid, they are then attracted to the oppositely charged metal plates.

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20
Q

Coulomb’s law

A

the force between two point charges is proportional to the square of the distance between them

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21
Q

ℨ

A

permitivity value

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22
Q

Definition of electric field strength

A

the electric field strength at a point in an electric field is the force acting on a test charge q, placed at a point divided by the magnitude of the charge

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23
Q

using coulomb’s law

E=

A

Q
___________
4 pi e dsqared

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24
Q

E

A

electric field strength

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25
Q
magnitude of charge causing electric field
26
d
distance
27
e
permitivity
28
how many decimal places should you put down for e
4 decimal places
29
charge of electron
pg 47 log tables
30
charge of proton
same as electron
31
alpha particle charge
half an electron
32
quark charges
the one in table is wrong
33
negative charge is not a negative when?
in calculations
34
definition of potential difference
the potential difference between points a and b is the work done per unit charge to move the charge from b to a
35
2 units for potential differents
J/C | Volt
36
other word for potential difference
voltage
37
simple explanation for voltage
ability to attract or repel
38
gain in kinetic energy formula
1/2 m v squared
39
work done to accelerate formula
Vq
40
formula for gain in kinetic energy and work done to accelerate
v sqared = 2Vq -------- m
41
V
potential difference (volt)
42
W
work done (joule)
43
q
charge (cuolomb)
44
m
mass (kg)
45
v
speed (m/s)
46
s
displacement (m/s/s)
47
definition of capacitance
the ratio of charge q on the object to the voltage of the object
48
C
capacitance
49
unit of capacitance
f = farad
50
1 farad =
1 coulomb / 1 volt
51
how big is capacitance usually?
very small around x X 10 -6 or x X 10 -12
52
what do capacitors consist of?
2 metal plates separated by an insulator
53
name of the insulator between capacitor plates
dielectric
54
what's the use of a capacitor
to store electrical charge
55
A in capacitors
common area
56
4 uses of capacitors
tuning a radio flash on a camera block dc flow and allow ac flow smoothing capacitor makes voltage constant
57
the build up of charge in a capacitor is...
non-linear
58
output of energy in a capacitor
non-linear
59
to charge a gold leaf electroscope by induction: | first step
bring a positively charged rod near the cap of the electroscope, the gold leaf rises, the leaf is positively charged and the cap i negatively charged
60
to charge a gold leaf electroscope by induction: | once the leaf is positively charged and the cap i negatively charged
touch the cap with your finger (earth it). the leaf falls as the charge in that region is neutralised, electrons come from the earth up to neutralise the positive charges
61
to charge a gold leaf electroscope by induction: | once it has been earthed
remove finger (earth connection) from the cap,then remove the positively charged rod, leaf rises again as negative charge from the cap spreads over the leaf region
62
to charge a gold leaf electroscope by induction: | conclusion
the gold leaf electroscope has been charged by induction
63
if you have 15 plates acting as capacitors, how many capacitors do you have
14
64
what is relative permitivity 1.5
Eo x 1.5
65
TO SHOW THE FACTORS THAT A CAPACITOR DEPENDS ON DISTANCE | what do you do
move the plates closer together and keep A and E constant
66
TO SHOW THE FACTORS THAT A CAPACITOR DEPENDS ON DISTANCE | what happens
smaller distance, larger capacitance | inversely proportional
67
TO SHOW THE FACTORS THAT A CAPACITOR DEPENDS ON COMMON AREA
slide them apart (less common area same distance) keep E and d constant smaller common area, smaller capacitance directly proportional
68
TO SHOW THE FACTORS THAT A CAPACITOR DEPENDS ON PERMITTIVITY
wax between plates A and d constant larger permittivity, larger capacitance directly proportional
69
charging a capacitor
positive curve | non linear
70
when the capacitor is fully charged
the current stops flowing and the voltage across the plates is the same as the voltage of a battery
71
DISCHARGING A CAPACITOR
discharge time very short negative curve output non-linear
72
DISCHARGING A CAPACITOR | what would happen to the electric field of the charged capacitor
would adversely affect surrounding electrical components
73
what type of current do capacitors allow
ac but not dc
74
how to charge a gold leaf electroscope by induction (3 steps)
1. bring a positively charged rod near the cap, leaf rises (positively charged), cap is negatively charged 2. touch the cap with your finger (earth it), leaf falls as is neutralised by electrons coming from the earth 3. remove finger, then remove positively charged rod, leaf rises again as electrons from cap move down to it
75
Charging a capacitor: | graph of charge over time
non linear, rises quickly and starts to level off
76
Charging a capacitor: | when a capacitor is fully charged
the current stops flowing and the voltage across the plates is the same as the voltage of the battery
77
Discharging a capacitor: | graph of charge over time
output is non-linear, discharge time very short - a few seconds
78
what would the electric field of a charged capacitor do?
it would adversely affect surrounding electrical components
79
circuit of a capacitor, a.c source and a bulb: | the larger the capacity of capacitor
the brighter the light from the bulb
80
circuit of a capacitor, a.c source and a bulb: | the higher the frequency of a.c supply
the brighter the bulb

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