Physics > P4.2 - Electrical Quantities > Flashcards

P4.2 - Electrical Quantities Flashcards

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1
Q

What’s the relationship between positive and positive charges? [1]

A

they repel

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2
Q

What’s the relationship between positive and negative charges? [1]

A

they attract

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3
Q

What’s the relationship between negative and negative charges? [1]

A

they repel

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4
Q

What happens to the force the closer the charges are? [1]

A

the greater the force between them

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5
Q

Where do charges come from? [1]

A
  • when two materials are rubbed together
  • electrons may be transferred from one to another
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6
Q

What are the charges of the materials being rubbed together? [2]

A
  • one has a net negative charge
  • one has a net positive charge
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7
Q

What are conductors? [1]

A
  • materials that let electrons pass through them
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8
Q

What are the best electrical conductors? [1]

A
  • metals
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9
Q

What makes ___ good thermal conductors and why? [2]

A
  • metals
  • because they have free electrons
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10
Q

What are insulators? [1]

A
  • materials that hardly conduct at all
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11
Q

Why don’t insulators conduct? [2]

A
  • electrons are held tightly to their atoms
  • not free to move
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12
Q

How can electrons be transferred? [1]

A

by rubbing - static charging

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13
Q

What are examples of insulators? [3]

A
  • plastics
  • glass
  • PVC
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14
Q

What are semi-conductors? [1]

A

neither an insulator or a conductor

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15
Q

What are the properties of semi-conductors? [2]

A
  • poor conductors when cold
  • better conductors when warm
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15
Q

What is charge measured in? [1]

A

Coulombs

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16
Q

What is Static Electricity? [2]

A
  • charges which are not free to move
  • charges are at rest
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17
Q

What does the charging of solids by friction involve? [1]

A

ONLY the transfer of negative charge (electrons)

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18
Q

What is an electric field? [2]

A

the region in which an electric charge experiences a force

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19
Q

How much is 1 micro coulomb in coulombs? [1]

A

10⁻⁶ C = one millionth of a coulomb

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20
Q

What are the two types of electricity? [2]

A
  • Static
  • Current
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21
Q

What is current? [2]

A
  • when charges are moving
  • when you can get the electrons to drift
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22
Q

What is an Electric Current? [1]

A

The rate of flow of charge

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23
Q

What is formula relating current and charge? [2]

A

Current = Charge / Time

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24
What is the symbol formula for current? [1]
I = Q / T
25
What is the unit for current? [1]
Amperes
26
What is A.C.? [2]
- when the current swings back and forth in every halfcycle
27
What is D.C? [1]
- current only flows in one direction
28
What is electrical conduction in metals? [1]
- the movement of delocalised electrons
29
Where is conventional current from? [1]
POSITIVE TO NEGATIVE
30
Where is the flow of electrons from? [1]
NEGATIVE TO POSITIVE
31
What is the use of an ammeter? [2]
- measures current - how much charge flows per second through the wire
32
What is the use of a voltmeter? [1]
tool used to measure voltage
33
What is Electromotive Force (E.M.F)? [3]
the electrical work done by a source in moving a unit charge around a complete circuit
34
What is E.M.F measured in? [1]
Volts
35
What is Potential Difference (P.D.)? [2]
the work done by a unit charge passing between two points in a circuit
36
What is P.D. measured in? [1]
Volts
37
What is the formula for resistance? [2]
Resistance = Voltage / Current
38
What is the symbol formula for Resistance? [1]
R = V / I
39
What is resistance? [2]
ratio of voltage to current in an appliance
40
What is the unit for Resistance? [1]
Ohms
41
Where is a Voltmeter meant to be connected? [1]
across the appliance
42
What's the formula for E.M.F? [2]
volts = joules / coulomb
43
What's the symbol formula for E.M.F? [1]
V = J / C
44
What's is Ohm's Law? [1]
voltage / current
45
What is Ohm's Law in symbols? [1]
V / I
46
Why is copper used for wiring? [2]
- good electrical conductor - cheap
47
What are some factors which affect resistance? [3]
- length - cross-sectional area - temperature
48
What is the relationship between length and resistance? [2]
R ∝ L
49
What does the relationship between length and resistance mean? [2]
- if length increases, resistance increases too
50
What is the relationship between temperature and resistance? [2]
- the greater the temperature, the greater the resistance
51
What is the relationship between the cross-sectional area of a wire and resistance? [2]
- the smaller the cross-sectional area of a wire, the greater the resistance
52
What are Ohmic conductors and how do their graphs look? [2]
- conductors which obey Ohm's Law - their I-V graph is a straight line through the origin
53
What are Non-Ohmic conductors and how do their graphs look? [2]
- conductors that do not obey Ohm's Law - their I-V graph is not a straight line and doesn't go through the origin
54
What is the formula for energy? [2]
Energy = Voltage x Current x Time
55
What is the symbol formula for energy? [1]
E = VIT
56
What is the formula for power? [2]
Power = Voltage x Current
57
What is the symbol formula for power? [1]
P = VI
58
How do you work out the total resistance in a series circuit? [1]
Rₜ = R₁ + R₂ + R₃
59
How do you work out the E.M.F of the source in a series circuit? [2]
- sum of PD across each - E.M.F. = V₁ + V₂ + V₃
60
What happens to the current if there's a bigger resistance in a parallel circuit? [1]
- current decreases
61
What happens to the current in a parallel circuit when it reaches a branch point? [1]
the current splits ups
62
How do you work out the total resistance in a parallel circuit? [2]
1/Rₜ = 1/R₁ + 1/R₂ + ...
63
How much voltage does each branch get in a parallel circuit? [1]
same voltage as the supply
64
How do I find out the total voltage in a parallel circuit? [2]
Vₜ = V₁ = V₂
65
What is the formula for power dissipated in a resistor? [2]
power = current² x resistance
66
What is the symbol formula for power dissipated in a resistor? [2]
P = I²R
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