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Past Difficulties Flashcards

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
what is the resultant force
The resultant force is the single force obtained by combining all the forces on the body
26
newtons second law
the rate if change of momentum on an object is directly proportional to the net force which acts on the object
27
newtons third law
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
definition for force
rate of change of momentum on a body
29
what is impulse
the change in momentum:
30
what is impulse on a force-time graph
the area under the graph
31
principle of conservation of momentum
The total momentum before a collision = the total momentum after a collision provided no external force acts
32
define external forces
External forces are forces that act on a structure from outside e.g. friction and weight
33
define internal forces
Internal forces are forces exchanged by the particles in the system e.g. tension in a string
34
define scalar quantities
calar quantities only have a magnitude
35
define vector quantities
Vector quantities have both magnitude and direction
36
how is the velocity shown on a displacement time graph
The gradient (or slope) equals velocity
37
how is the initial discplacement shown on a displacement time graph
The y-intercept equals the initial displacement
38
define electric current
Electric current is defined as the rate of flow of positive charge carriers
39
how is a coulumb defined
This is defined as the quantity of charge that passes a fixed point per second when a current of 1 A is flowing
40
another definition for electric current
Electric current is the rate of flow of charge carriers
41
definition of an electrolyte
An electrolyte is a substance that produces an electrically conducting solution
42
kirchoffs first law
The sum of the currents entering a junction always equal the sum of the currents out of the junction
43
what are conductors
conductors are materials that have a very high number density often in the range of 10^28
44
what are semiconductors
Semiconductors are materials that have a conductivity between conductors and insulators
45
what are characteristics of semi conductors
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
what is resistance
the opposition to current
47
what is ohms law
For a conductor at a constant temperature, the current through it is proportional to the potential difference across it
48
what does an iv graph for an ohmic onductor look like
This is demonstrated by the straight-line graph through the origin
49
how do you know an electrical component obeys ohms law when looking at an IV graph
An electrical component obeys Ohm’s law if its graph of current against potential difference is a straight line through the origin
50
iv for semiconductor diode
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
what happens to the resistance for an LDR
As the light intensity increases, the resistance of an LDR decreases
52
uses of LDR
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
what causes electrical heating
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
if you double the length of a wire, what will happen to the resistance
it will also double
55
what is resistivity
Resistivity is a property that describes the extent to which a material opposes the flow of electric current through it
56
how does resistance vary on a thermistor
hermistors are negative temperature coefficient (ntc) components This means that if the temperature increases, the resistance of the thermistor decreases (and vice versa)
57
kirchoffs second law
The sum of the e.m.f’s in a closed circuit equals the sum of the potential differences
58
What is a progressive wave
A wave that carries energy from one point to another without transferring any matter
59
Speed of a wave equation
Speed of wave = frequency x wavelength
60
What is diffraction
This is the way that waves spread out as they come through a narrow gap or around obstacles

Physics (13 decks)

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