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Physics > Past Difficulties > Flashcards

Past Difficulties Flashcards

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1
Q

define a brittle material

A

A material that fractures before plastic deformation

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2
Q

what are characteristics of a brittle material

A

Elastic behaviour is shown until the breakpoint where the material snaps.
There is no plastic deformation, and the loading and unloading curves are the same

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3
Q

name 2 examples of a brittle material

A

Brittle materials include: glass, ceramic

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4
Q

what is a ductile material

A

A material that can withstand large plastic deformation without breaking

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5
Q

what are characteristics of a ductile material

A

They generally experience elastic deformation up until their elastic limit
After this, they then undergo plastic deformation before reaching their ultimate tensile stress and breakpoint
For this reason, they can be easily hammered into thin sheets or drawn into long wires

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6
Q

name a ductile material

A

copper

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7
Q

define a polymeric material

A

A material made up of long, repeating chains of molecules

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8
Q

what are characteristics of polymeric materials

A

They can endure a lot of tensile stress before breaking
There is no elastic deformation, but the unloading curve is different to the loading curve, as some energy has been lost as thermal energy

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9
Q

name 2 examples of polymeric materials

A

rubber, polythene

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10
Q

define the yield stress of a stress strain graph

A

the force per unit area at which the material extends plastically for a small increase in stress

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11
Q

define the breaking point

A

The stress at this point is the breaking stress
This is the maximum stress a material can stand before it fractures

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12
Q

define the elastic region

A

The region of the graph up until the elastic limit
In this region, the material will return to its original shape when the applied force is removed

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13
Q

define the plastic region

A

The region of the graph after the elastic limit
In this region, the material has deformed permanently and will not return to its original shape when the applied force is removed

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14
Q

what is a tensile force

A

When two forces stretch a body

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15
Q

what is a compressive force

A

When two forces compress a body

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16
Q

hookes law

A

The extension of the material is directly proportional to the applied force (load) up to the limit of proportionality

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17
Q

what does the spring constant measure

A

the stiffness of a material

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18
Q

how is hookes law shown on a force extension graph

A

This is shown on its force-extension graph by a straight line through the origin

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19
Q

where is elastic potential energy stored

A

Before a material reaches its elastic limit (whilst it obeys Hooke’s Law), all the work done is stored as elastic potential energy

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20
Q

elastic potential energy definition

A

The energy stored within a material (e.g. in a spring) when it is stretched or compressed

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21
Q

definition of tensile stress

A

Tensile stress is defined as the force exerted per unit cross-sectional area of a material

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22
Q

ultimate tensile stress defnition

A

The ultimate tensile stress is the maximum force per original cross-sectional area a wire is able to support until it breaks

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23
Q

youngs modulus definition

A

The measure of the ability of a material to withstand changes in length with an added load

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24
Q

newtons first law

A

A body will remain at rest or move with constant velocity unless acted on by a resultant force

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25
Q

what is the resultant force

A

The resultant force is the single force obtained by combining all the forces on the body

26
Q

newtons second law

A

the rate if change of momentum on an object is directly proportional to the net force which acts on the object

27
Q

newtons third law

A

If body A exerts a force on body B, then body B will exert a the same type of force on body A of equal magnitude but in the opposite direction

28
Q

definition for force

A

rate of change of momentum on a body

29
Q

what is impulse

A

the change in momentum:

30
Q

what is impulse on a force-time graph

A

the area under the graph

31
Q

principle of conservation of momentum

A

The total momentum before a collision = the total momentum after a collision provided no external force acts

32
Q

define external forces

A

External forces are forces that act on a structure from outside e.g. friction and weight

33
Q

define internal forces

A

Internal forces are forces exchanged by the particles in the system e.g. tension in a string

34
Q

define scalar quantities

A

calar quantities only have a magnitude

35
Q

define vector quantities

A

Vector quantities have both magnitude and direction

36
Q

how is the velocity shown on a displacement time graph

A

The gradient (or slope) equals velocity

37
Q

how is the initial discplacement shown on a displacement time graph

A

The y-intercept equals the initial displacement

38
Q

define electric current

A

Electric current is defined as the rate of flow of positive charge carriers

39
Q

how is a coulumb defined

A

This is defined as the quantity of charge that passes a fixed point per second when a current of 1 A is flowing

40
Q

another definition for electric current

A

Electric current is the rate of flow of charge carriers

41
Q

definition of an electrolyte

A

An electrolyte is a substance that produces an electrically conducting solution

42
Q

kirchoffs first law

A

The sum of the currents entering a junction always equal the sum of the currents out of the junction

43
Q

what are conductors

A

conductors are materials that have a very high number density often in the range of 10^28

44
Q

what are semiconductors

A

Semiconductors are materials that have a conductivity between conductors and insulators

45
Q

what are characteristics of semi conductors

A

Their conductivity depends on their temperature
At low temperatures, their resistivity rises, therefore their conductivity falls
At high temperatures, their resistivity falls, therefore their conductivity rises
Metal conductors behave in the opposite way

46
Q

what is resistance

A

the opposition to current

47
Q

what is ohms law

A

For a conductor at a constant temperature, the current through it is proportional to the potential difference across it

48
Q

what does an iv graph for an ohmic onductor look like

A

This is demonstrated by the straight-line graph through the origin

49
Q

how do you know an electrical component obeys ohms law when looking at an IV graph

A

An electrical component obeys Ohm’s law if its graph of current against potential difference is a straight line through the origin

50
Q

iv for semiconductor diode

A

forward bias is shown by the sharp increase in potential difference and current on the right side of the graph

reverse bias is shown by a zero reading of current or potential difference on the left side of the graph which then goes steeply vertically down

51
Q

what happens to the resistance for an LDR

A

As the light intensity increases, the resistance of an LDR decreases

52
Q

uses of LDR

A

LDRs can be used as light sensors, so, they are useful in circuits which automatically switch on lights when it gets dark, for example, street lighting and garden lights

53
Q

what causes electrical heating

A

free electrons move through a metal wire, they collide with ions which get in their way
As a result, they transfer some, or all, of their kinetic energy on collision, which causes electrical heating

54
Q

if you double the length of a wire, what will happen to the resistance

A

it will also double

55
Q

what is resistivity

A

Resistivity is a property that describes the extent to which a material opposes the flow of electric current through it

56
Q

how does resistance vary on a thermistor

A

hermistors are negative temperature coefficient (ntc) components

This means that if the temperature increases, the resistance of the thermistor decreases (and vice versa)
57
Q

kirchoffs second law

A

The sum of the e.m.f’s in a closed circuit equals the sum of the potential differences

58
Q

What is a progressive wave

A

A wave that carries energy from one point to another without transferring any matter

59
Q

Speed of a wave equation

A

Speed of wave = frequency x wavelength

60
Q

What is diffraction

A

This is the way that waves spread out as they come through a narrow gap or around obstacles

Physics (12 decks)

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