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BMAT > Physics > Flashcards

Physics Flashcards

1
Q

What are insulators?

A
  • materials that inhibit the flow of electrical current

- the opposite of conductors, which allow electric particles to flow freely

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2
Q

What are conductors?

A
  • substance where electrons, move easily from atom to atom

- with the application of voltage

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3
Q

What is conductivity? And examples of good conductors?

A
  • the capacity to transmit something, such as electricity or heat
  • Copper, steel, gold, aluminum, and brass
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4
Q

How are insulators charged?

A
  • by friction (when they are rubbed together)
  • a substance that gains electrons becomes negatively charged
  • a substance that loses electrons becomes positively charged
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5
Q

Charging is caused by what?

A

Loss or gain of electrons

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6
Q

Like charges do what?

A

Repel

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7
Q

Unlike charges do what?

A

Attract

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8
Q

Applications of electrostatics

A
  • one main use: printers and photocopiers where static electric charges attract the ink, or toner, to the paper
  • other uses include paint sprayers, air filters, and dust removal.
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9
Q

Problems with static electricity

A
  • can build up in clouds, can cause a huge spark to form between ground and cloud. Causes lightning – a flow of charge through the atmosphere
  • dangerous when there are flammable gases or a high conc of oxygen - spark could ignite the gases + cause an explosion.
  • dangerous when you touch something with a large electric charge on it - the charge will flow through body causing an electric shock
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10
Q

Describe what the dangers are of static electricity when refuelling aircraft tanks, what stops this from occurring?

A
  • If the fuel passing along the hose to vehicle was allowed to build up a static charge, a resulting spark might ignite the fuel
  • The hoses are earthed to stop this occurring
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11
Q

What does it mean for something to be earthed?

A
  • connected to ground directly or indirectly so that electric charge flows from an object
  • preventing dangerous build-up of static electricity
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12
Q

How is static electricity used in paint spraying?

A
  • paint spray goes past a high voltage positive needle
    as it leaves the spray gun
  • tiny droplets of paint pick up a positive charge (lose and e-)
  • car body given a high voltage negative charge
    which attracts the positively charged paint droplets
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13
Q

State two ways in why paint spraying using static electricity is efficient

A

1 paint droplets spread out more as they leave the gun - happens because they all get the same positive
charge and so they all repel each other
2 paint droplets attracted to negative
metal car body so less paint will be wasted
by landing on the floor

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14
Q

What is static electricity?

A
  • an electrical charge produced by friction that causes sparks or crackling, can also attract dust and hair
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15
Q

Describe how static electricity is used in dust extraction

A
  • used in pollution control
  • by applying a static charge to dirt particles in the air and then collecting those charged particles on a plate or collector of the opposite electrical charge.
  • device known as electrostatic precipitators
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16
Q

Why does smoke need to be removed and how is it done?

A
  • power stations burn fossil fuels like coal and oil - smoke produced, smoke comprises tiny solid particles, like unreacted carbon, which can damage buildings and cause breathing difficulties
  • Electrostatic precipitators
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17
Q

Describe (in 3 steps) how an electrostatic precipitator works

A

1 Smoke particles pick up a negative charge.
2 Smoke particles are attracted to the collecting plates.
3 Collecting plates are knocked to remove the smoke particles.

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18
Q

What’s an electric current?

A
  • the rate of flow of electric charge
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19
Q

An electric current flows when?

A
  • when electrons move through a conductor e.g. a metal wire.
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20
Q

Definition of current

A
  • the flow of negatively charged electrons, from negative to positive
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21
Q

What’s ‘conventional current’?

A
  • original definition of current (which is wrong)

- the flow of charges from positive to negative

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22
Q

Calculation for current

A 
current (in amps) = charge in (coulombs) / time (in seconds)
or I= Q/T
I - current
Q - charge
T - time
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23
Q

What is amperes?

A
  • amperes, amps, A is the unit of current
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24
Q

What is coulombs?

A
  • coulombs, C is the unit of charge
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25
Q

What is voltage?

A
  • measure of how much energy the electrons are carrying around to the things in the circuit
  • measured in (V) volts
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26
Q

What is resistance?

A
  • measure of how hard it is for the electrons to travel through a part of the circuit - measured in Ohms, Ω
27
Q

Use of a voltmeter

A
  • measures voltage (potential difference) across a component
28
Q

Use of ammeter

A
  • ammeter needs to measure the flow of charge, so it is in a series
  • means that all the charge has to flow through it and can be counted
  • also means that an ammeter needs to have a very low resistance
29
Q

Why is a voltmeter in parallel?

A
  • the voltmeter compares the energy difference between two points in a circuit, to see how much has been used up
  • means it is in parallel
30
Q

Why does the voltmeter need to have high resistance?

A
  • otherwise all the current would flow through the meter instead of the component
31
Q

Structure of a parallel circuit

A
  • ## current divides into two or more paths before recombining to complete the circuit
32
Q

Structure of a series circuit

A
  • connected to a circuit in a way that same current flows through each component in turn
  • opposite of in parallel
33
Q

There is a resistance to the flow of an electric current through most what?

A

conductors

34
Q

Resistance in a wire increases as what two things increase/decrease?

A
  • the length of the wire increases

- the thickness of the wire decreases

35
Q

What causes resistance in circuits?

A
  • moving electrons colliding with the ions in the metal

- makes it more difficult for the current to flow therefore resistance

36
Q

Describe the relationship between wire length and resistance

A
  • resistance of a long wire is greater than the resistance of a short wire because electrons collide with more ions as they pass through
  • relationship between resistance and wire length is proportional
37
Q

Describe the relationship between wire thickness and resistance

A
  • resistance of a thin wire is greater than the resistance of a thick wire because a thin wire has fewer electrons to carry the current
  • relationship between resistance and the area of the cross section of a wire is inversely proportional.
38
Q

What happens to current when resistance increases?

A
  • when resistance is increased in a circuit, (e.g. by adding more electrical components) the current decreases as a result.
39
Q

Calculating resistance equation

A 
re-arrange this: voltage = current × resistance into 
R = V ÷ I
R - resistance (Ω, Ohms)
V - Voltage (V, volts)
I - current  (A, amps)
40
Q

What increases as potential difference (voltage) increases?

A
  • for given amount of electrical charge that moves, amount of energy transferred increases as potential difference increases
41
Q

Calculating energy transferred equation

A
  • energy transferred = potential difference × charge
  • E = V × Q
    E - energy (joules, J)
    V - volts (amps, A)
    Q - charge (coulombs, C)
42
Q

How can volts be defined in terms of its equation?

A

one volt as one joule per coulomb

V = E / Q

43
Q

x and y axis on a force-extension graph

A 
x= extension (m)
y= force (N)
44
Q

describe the force-extension graph

A
  • extension directly proportional to force applied (so steady increasing line)
  • begins to plateau (change) at limit of proportionality and is now non-linear
45
Q

limit of proportionality also referred to as?

A
  • elastic limit
46
Q

Where is non-linear extension and inelastic deformation seen on a force-extension graph?

A
  • above limit of proportionality
47
Q

gradient of force-extension graph before limit of proportionality shows what?

A

spring constant

48
Q

what is the limit of proportionality ?

A
  • furthest point material can be stretched/deformed while being able to return back to its original shape
49
Q

What is Hooke’s law?

A

force = spring constant x extension

50
Q

What’s elastic deformation?

A
  • reversed when force removed
51
Q

What’s inelastic deformation?

A
  • not fully reversed when force is removed

- permanent change in shape

52
Q

what’s extension(1) and what is compression(2) ?

A

(1) object increases in length

(2) object decreases in length

53
Q

Units of spring constant (k) in Hooke’s law

A

N/m Newtons per meters

54
Q

Units of extension in Hooke’s law

A

m Meters

- its the INCREASE in length

55
Q

what does a higher spring constant indicate?

A
  • a stiffer spring
56
Q

energy stored in a spring is called what?

A

the elastic potential energy

57
Q

elastic potential energy calculation

A

Ee= 0.5Ke(squared)

so 1/2 x spring constant x extension (sqaured)

58
Q

State newtons first law

A
  • if a body is at rest and the forces acting on it are balanced then the body will remain at rest
59
Q

State newtons second law

A

force(N) = mass (kg) x acceleration (m s-2)

60
Q

What’s inertia?

A

Inertia is a resistance to a change in motion

61
Q

how does mass affect an object’s inertia?

A

more mass means more inertia

62
Q

what’s needed to change the motion of an object with high inertia?

A

a greater resultant force

63
Q

describe the motion of a car with 5000N drag and 5000N thrust

A
  • forces acting on this car are balanced
  • thrust is equal and opposite to the drag
  • no net (resultant) force as the forces add up to zero
  • car will be travelling at constant speed in a straight line
64
Q

State Newton’s 3rd Law

A
  • ‘if body A exerts a force on body B then body B exerts an equal and opposite force of the same type on body A’

BMAT (3 decks)

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