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Physics ATAR U1 > Electricity > Flashcards

Electricity Flashcards

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1
Q

What is charge

A

Where particles have positive / negative / neutral charge

Like charges repel, opposite charges attract

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2
Q

What are electric forces

A

Non-contact

Vector quantity (Has magnitude and direction)

Strength of force depends on distance between charges
- Greater unbalanced charge = Greater force

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3
Q

What are electrical conductors

A

Electrons free to move, charge can flow easily

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4
Q

What are electrical insulators

A

Electrons can’t move, charge can’t flow

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5
Q

What are electrical semi-conductors

A

Conducts electricity under certain circumstances

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6
Q

What is current

A

The flow of electric charge, net amount of charge passing certain point in given time interval

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7
Q

What do you need for current

A

An electric field, supply energy to move charges

Charges being free to move

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8
Q

How to measure current in circuits

A

Current is conserved quantity, charge carriers always somewhere

Current that flows in = Current that flows out

Measured using ammeter, connected anywhere

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9
Q

What is formula for current

A

Current (A) = Charge (C) / Time (s)

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10
Q

What is Direct-Current (DC)

A

Net charge flows in 1 direction, power from batteries

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11
Q

What is Alternating-Current (AC)

A

Charge flow alternates, moves back and forth, power from wall socket

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12
Q

What is electric potential

A

Potential energy per unit of charge (Coulomb)

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13
Q

What is potential energy

A

“Stored” energy with capacity to do work
- Gravitational Potential Energy
- Elastic Potential Energy
- Electric Potential Energy

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14
Q

What is potential difference / voltage

A

Change in potential energy per unit charge between two defined points in circuit

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15
Q

Why do electrons require energy to move

A

Charged particles naturally move from high to low potential

Requires energy to move from low to high potential = Electrons require energy to move

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16
Q

What is 1 volt

A

1 J/ Coulomb

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17
Q

How do you measure potential difference using voltmeter

A

Measured by comparing two different locations on circuit

Exists if charged particles gain/lose potential energy

Measured using voltmeter

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18
Q

What is formula for potential difference

A

Voltage = Change in Potential Energy / Work (J) / Electric Charge (C)

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19
Q

How do you create a current

A

Potential difference applied to conductor

  • Creates electric field
  • Exorts force on electric charges
  • Electric charges move = Current
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20
Q

What is power

A

Rate of energy transfer

Power usage of element determined from voltage & current of element

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21
Q

What are the formulas of power

A

Power = Work Done (J) / Time (s)

Power = Voltage (V) * Current (A)

22
Q

What is a circuit

A

Path through where electricity flows

23
Q

What are the requirements for a circuit

A

Power source, produces EMF

Complete path of conducting material

24
Q

What is a series circuit

A

All elements arranged in chain, only one path for current

25
Q

What is the resistance in a series circuit

A

Total Resistance = Sum of individual resistances

Rt = R1 + R2 + R3 + …

26
Q

What is voltage in a series circuit

A

Total Voltage = Sum of individual voltages

Vt = V1 + V2 + V3 + …

27
Q

What is current in a series circuit

A

Current is the same in every part of circuit

Current in = Current out

28
Q

What is a parallel circuit

A

Each component directly connected to power source

Atleast two pathways for current to travel

29
Q

What is the resistance in a parallel circuit

A

Total Resistance = Amount of resistance a ‘single’ resistor needs to equal overall effect

1 / Rt = (1/R1) + (1/R2) + (1/R3) + …

30
Q

What is the voltage in a parallel circuit

A

Same voltage applied to each pathway of circuit

31
Q

What is the current in a parallel circuit

A

Current in = Current out

Current split between each branch

Split equally if resistance of each branch is the same

32
Q

What is electrical resistance

A

Measure of how hard it is for current to flow through material

33
Q

How does resistance work in wires

A

Charge moves through wire in zig-zags, as it collides with atoms

In collisions, charges transfer some energy to atoms = Being resisted

34
Q

How does resistivity affect resistance

A

How much a material opposes flow of charge

Some materials resist movement of charge more than others

35
Q

How does temperature affect resistance

A

Increase in temperature = Increase in resistance

Atoms vibrate faster, charge through conductor has more collisions

36
Q

How does length of wire affect resistance

A

Longer wire = Higher resistance

Charges experience more collisions before reaching end of wire

37
Q

How does area of wire affect resistance

A

Higher area = Lower resistance

More area for charges to move = Less collisions

38
Q

What is Ohm’s Law

A

Current flowing through substance directly proportional to voltage

Resistance affects current & voltage

39
Q

What is the formula for resistance

A

Resistance (Ohms) = Voltage (V) / Current (A)

40
Q

What are ohmic devices

A

Resistance constant for wide range of voltages & currents

Obeys Ohm’s Law

Most wires & resistors

41
Q

What are non-ohmic devices

A

Resistance not constant, varies depending on current & voltage

Doesn’t obey Ohm’s Law

Light diodes, digital devices

42
Q

What are thermal hazards

A

Excessive electric power, undesired thermal effect

Eg. Starting a fire in the wall of a house

43
Q

What are short circuits

A

Low resistance path between positive & negative terminals of voltage source

  • Resistance small, power large = Melt / Cause Fire
44
Q

What are shock hazards

A

Current passes through body (Severely painful to lethal)

  • Voltage related to flow, energy available for flow

Amount of current depends on bodies resistance
- Dry skin = High resistance (Good)
- Wet skin = Low resistance, can be lethal (Bad)

45
Q

What are electric shock fatalities

A

Current puts heart into fibrillation (Irregular heartbeat)

Effect of shock depends on:
- Amount of current
- Path of current
- Duration of shock
- Frequency of current

46
Q

How do you prevent electrical shocks)

A

Unplug appliances when working on / cleaning them

Keep appliances dry, use dry hands

Qualified professionals do maintenance

Touch something ‘live’ with back of hand, if muscles contract, will pull away from object instead of grabbing it

47
Q

What is a fuse and circuit breaker, and what is the difference

A

Wire overload

Innner wires overheat & melt when current too high (Breaks circuit)

Limits excessive currents

Works for small voltages / currents (Eg. Household)

Won’t save from electrocution

Circuit breakers can be reset, fuses need to be replaced

48
Q

What are the types of wires in a household

A

Active Wire: Carries current from power station

Neutral Wire: Closes circuit so current can flow

Earth Wire: Safety device, connected to conductive parts of appliances

49
Q

What does an earth wire do

A

If active wire in metal case touches the metal casing, whole case becomes electrically live

To prevent this, a short circuit is created by earth wire, current immediately flows to the Earth

50
Q

What is double insulation

A

Device never exposes operator to active wire even if it becomes disconnected / loose

  • Done by ensuring outer casing insulated from inner workings
  • Earth wire not needed
51
Q

What are residual current devices (RCDs)

A

Cuts the circuit when Active Current != Neutral Current

  • Should be the same as current in = current out
  • If not same, leakage of current (Eg. To Earth or To Person)

Cuts at as little different as 30mA

Physics ATAR U1 (6 decks)

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