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PHSI > Module 4: Electricity > Flashcards

Module 4: Electricity Flashcards

1
Q

Electric force

A

The force responsible for binding nuclei and electrons to form atoms, binding atoms to form molecules, and binding molecules to form bulk materials

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2
Q

What does electrical force act upon?

A

Charged objects

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3
Q

Unit for charge

A

C coulombs

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4
Q

Smallest nonzero charge an object can have

A

qe

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5
Q

Value of qe

A

1.6 x 10^-19 C

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6
Q

Describe charging by friction

A

Electrons are transferred from one insulator to another when they are rubbed together

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7
Q

Conductor

A

A material where charge can move freely

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8
Q

Insulator

A

A material where charge cannot move freely

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9
Q

Two examples of conductors

A

Metals

Salty water

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10
Q

Four examples of insulators

A

Plastics
Oil
Glass
Undissolved salt

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11
Q

Do conductors have a high or low resistivities?

A

Low

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12
Q

Do insulators have high or low resistance?

A

High

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13
Q

Polarisation

A

The separation of charges in a neutral object

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14
Q

In which materials does polarisation occur to a larger extent?

A

Conductors

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15
Q

|q|

A

Absolute value of charge

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16
Q

In which direction does an electric field go?

A

Positive to negative

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17
Q

Function of a battery

A

Kees constant potential difference across terminals

18
Q

How can we increase the capacitance? (3)

A

Decrease distance between plates
Increase size of plates
Add a capacitor in parallel

19
Q

Relative permittivity

A

Range between 1-100

Can find actually permittivity by multiplying this with the permittivity of a vaccum

20
Q

What circuit component does a cell membrane (and fluid around it) act like?

A

Capacitor

Membrane is insulator between two ‘plates’ of salty water

21
Q

How does capacitance relate to our reaction times?

A

The capacitance of nerve cell membranes determines how fast you can think

The smaller the capacitance, the faster the reaction time

22
Q

Which has a larger capacitance: capacitors in series or parallel?

A

Parallel

23
Q

Which has a larger resistance: resistors in series or in parallel?

A

Series

Current can split through two resistors in parallel

24
Q

Conventional current

A

The current in the direction of positive charge flow

Opposite direction to conduction (movement of electrons)

25
Q

What property determines a specific objects resistance?

A

It’s geometry (additional to the materials resistance)

26
Q

Kirchoffs law #1

A

The sum of potential charges around a loop is zero

Due to conservation of energy

27
Q

Kircchoffs law #2

A

The current flowing into a junction is the same as the current flowing out

Due to conservation of charge

28
Q

What happens to electrical energy as it passes through a resistor?

A

They lose energy- bashing into the metal atoms of the resistor

This energy is converted into heat

29
Q

Why don’t electrons slow down as they travel ‘through’ the battery, like they do in a resistor?

A

The battery provides chemical energy- which is converted into electrical energy in the electrons

30
Q

If potential is decreased in the direction of current flow, what happens to the power?

A

Dissipates

31
Q

How do we increase the potential in the direction of current flow?

A

Power input

32
Q

If two lights are connected in series, will they be as bright as one?

A

No- resistance is doubled (and voltage stays the same) so the current is halved

Power is halved

33
Q

What happens to the brightness if we add two lightbulbs in parallel?

A

Same brightness- resistance is halved, so current is doubled

Power is doubled through two lights- so each is the same as before

34
Q

Four factors determining how dangerous an electric shock can be

A

Amount of current (not voltage)

Path taken by current (through body)

Duration of shock

Frequency (DC more dangerous than AC)

35
Q

Why is most electrical interference (e.g. defibrillator) done through the skin?

A

Because skin provides a large resistance that prevents current through the body from being too large

36
Q

RC circuit

A

Resistor and capacitor in series

37
Q

When does the charging of a capacitor finish?

A

When the voltage across the capacitor = voltage across the resistor

38
Q

What happens to the rate of charge in a capacitor when discharging? What is this called?

A

Decreases as current approaches zero

Exponential decay

39
Q

RC

A

Time constant/ RC constant

Time taken for charge to drop to 37% of previous value

40
Q

For a circuit that quickly reaches equilibrium, will the time constant be small or large?

A

Small- small resistance and capacitance

PHSI (6 decks)

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