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Physics > Electricity 1 > Flashcards

Electricity 1 Flashcards

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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

Q

A

magnitude of charge causing electric field

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26
Q

d

A

distance

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27
Q

e

A

permitivity

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28
Q

how many decimal places should you put down for e

A

4 decimal places

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29
Q

charge of electron

A

pg 47 log tables

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30
Q

charge of proton

A

same as electron

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31
Q

alpha particle charge

A

half an electron

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32
Q

quark charges

A

the one in table is wrong

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33
Q

negative charge is not a negative when?

A

in calculations

34
Q

definition of potential difference

A

the potential difference between points a and b is the work done per unit charge to move the charge from b to a

35
Q

2 units for potential differents

A

J/C

Volt

36
Q

other word for potential difference

A

voltage

37
Q

simple explanation for voltage

A

ability to attract or repel

38
Q

gain in kinetic energy formula

A

1/2 m v squared

39
Q

work done to accelerate formula

A

Vq

40
Q

formula for gain in kinetic energy and work done to accelerate

A

v sqared = 2Vq
——–
m

41
Q

V

A

potential difference (volt)

42
Q

W

A

work done (joule)

43
Q

q

A

charge (cuolomb)

44
Q

m

A

mass (kg)

45
Q

v

A

speed (m/s)

46
Q

s

A

displacement (m/s/s)

47
Q

definition of capacitance

A

the ratio of charge q on the object to the voltage of the object

48
Q

C

A

capacitance

49
Q

unit of capacitance

A

f = farad

50
Q

1 farad =

A

1 coulomb / 1 volt

51
Q

how big is capacitance usually?

A

very small around x X 10 -6 or x X 10 -12

52
Q

what do capacitors consist of?

A

2 metal plates separated by an insulator

53
Q

name of the insulator between capacitor plates

A

dielectric

54
Q

what’s the use of a capacitor

A

to store electrical charge

55
Q

A in capacitors

A

common area

56
Q

4 uses of capacitors

A

tuning a radio
flash on a camera
block dc flow and allow ac flow
smoothing capacitor makes voltage constant

57
Q

the build up of charge in a capacitor is…

A

non-linear

58
Q

output of energy in a capacitor

A

non-linear

59
Q

to charge a gold leaf electroscope by induction:

first step

A

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
Q

to charge a gold leaf electroscope by induction:

once the leaf is positively charged and the cap i negatively charged

A

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
Q

to charge a gold leaf electroscope by induction:

once it has been earthed

A

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
Q

to charge a gold leaf electroscope by induction:

conclusion

A

the gold leaf electroscope has been charged by induction

63
Q

if you have 15 plates acting as capacitors, how many capacitors do you have

A

14

64
Q

what is relative permitivity 1.5

A

Eo x 1.5

65
Q

TO SHOW THE FACTORS THAT A CAPACITOR DEPENDS ON DISTANCE

what do you do

A

move the plates closer together and keep A and E constant

66
Q

TO SHOW THE FACTORS THAT A CAPACITOR DEPENDS ON DISTANCE

what happens

A

smaller distance, larger capacitance

inversely proportional

67
Q

TO SHOW THE FACTORS THAT A CAPACITOR DEPENDS ON COMMON AREA

A

slide them apart (less common area same distance)
keep E and d constant
smaller common area, smaller capacitance
directly proportional

68
Q

TO SHOW THE FACTORS THAT A CAPACITOR DEPENDS ON PERMITTIVITY

A

wax between plates
A and d constant
larger permittivity, larger capacitance
directly proportional

69
Q

charging a capacitor

A

positive curve

non linear

70
Q

when the capacitor is fully charged

A

the current stops flowing and the voltage across the plates is the same as the voltage of a battery

71
Q

DISCHARGING A CAPACITOR

A

discharge time very short
negative curve
output non-linear

72
Q

DISCHARGING A CAPACITOR

what would happen to the electric field of the charged capacitor

A

would adversely affect surrounding electrical components

73
Q

what type of current do capacitors allow

A

ac but not dc

74
Q

how to charge a gold leaf electroscope by induction (3 steps)

A
  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
Q

Charging a capacitor:

graph of charge over time

A

non linear, rises quickly and starts to level off

76
Q

Charging a capacitor:

when a capacitor is fully charged

A

the current stops flowing and the voltage across the plates is the same as the voltage of the battery

77
Q

Discharging a capacitor:

graph of charge over time

A

output is non-linear, discharge time very short - a few seconds

78
Q

what would the electric field of a charged capacitor do?

A

it would adversely affect surrounding electrical components

79
Q

circuit of a capacitor, a.c source and a bulb:

the larger the capacity of capacitor

A

the brighter the light from the bulb

80
Q

circuit of a capacitor, a.c source and a bulb:

the higher the frequency of a.c supply

A

the brighter the bulb

Physics (11 decks)

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