Definitions 2 Flashcards
Brittle materials
Materials which do not undergo plastic deformation. Force is proportional to extension until it breaks
Ductile materials
Materials which undergo plastic deformation after a considerable elastic deformation. Initially force is proportional to extension then a large extension for a small change in force
Elastic deformation
Object returns to its original length (zero extension) when load is removed
Force-extension graph
The area under such a graph is the work done in stretching the material; for the straight-line portion of the graph, it is a measure of the elastic potential energy stored by the material
Hooke’s law
Force/load is proportional to extension/compression if proportionality limit is not exceeded
Plastic deformation
Body does not return to its original shape/length when load is removed
Strain
Extension over original length (ratio); stress is the cause and strain is the effect
Stress
It is the force per uint cross-sectional area required to stretch a material
Ultimate tensile strength
The maximum value of stress that an object can sustain before it breaks
Ultimate tensile stress
The maximum value of stress that an object can sustain before it breaks
Young’s modulus
Ratio of stress to strain
Electric current
The amount of charge flowing pass a point per unit time or rate of flow of charged particles
Potential difference
Potential difference is the difference in or amount of electrical potential energy per unit charge between two points because some of the energy is converted to other forms
E.M.F
The amount of chemical energy converted into electrical energy per unit charge supplied
Potential divider
Series circuits which produce an output voltage as a fraction of its input voltage
The ratio of the output voltage to the input voltage = the ratio of the output resistance over the total resistance
What is the unified atomic mass unit (u)?
It is the standard unit of mass for atomic particles; it is roughly equal to the mass in kg of one proton or one neutron: 1.66x10^-27 kg
1 elementary charge of an electron or proton
How many coulombs does an electron or proton have?
An electron or proton consists of +/- 1.6x10^-19 coulombs (C)
What is the value of one coulomb?
6.24x10^18 electrons or protons
State the masses of alpha, beta and gamma rays:
State the speeds of alpha, beta and gamma rays:
State the masses of alpha, beta and gamma rays:
How do you calculate the mass of an element in u?
It’s mass is equal to the sum of its protons and neutrons = nucleon number
Equation for the number of charge carriers
Q = ne
Q = total charge transferred
e = 1.6 x 10^-19 (the charge on one electron)
Work done
The amount of energy transferred from one place to another
The equation for work done
W = Fscosθ
F = force in N
s = displacement in m
To use this equation, there must be a component of the force that is in the same direction as the displacement
When is work done positive or negative?
- Work done is a force acts in the direction that an object is moving
- Work done is negative in a force acts in the opposite direction to the movement
The principle of conservation of energy
Energy cannot be created or destroyed, it can only be transferred from one energy store to another
Energy dissipation
This is used to describe ways in which energy is wasted
Efficiency
The ratio of the useful energy output from the system to the total energy input
The equation for efficiency
Efficiency = useful energy output / total energy input
OR
Efficiency = useful power output / total power input
Power
The work done or energy transferred per unit time
The equation for power
P = W/t = E/t
The equation for the power of a moving object
P = Fv
When do you use P = Fv?
When a constant force moves a body at a constant velocity; the force must be applied in the same direction as the velocity
How do you derive P = Fv?
Power is the rate of doing work: P = W/t
→
Work is done when a force moves an object over a distance: W = Fs
At a constant velocity, the distance moved by the object can be described as: d = vt
→
Substituting this into the work done equation gives: W = Fvt
→
And substituting this into the power equation gives: P = Fv
Kinetic energy
The energy an object has due to its motion
How do you derive EK = (1/2)mv^2?
The work done in accelerating a mass is: W = Fs
→
Newton’s 2nd law states that: F = ma
→
The SUVAT equation for velocity is: v^2 = u^2 + 2as
→
If u = 0, then: v^2 = 2as
→
Rearrange to make a the subject: a = v^2 / 2s
→
Substituting this a into Newton’s 2nd law gives: W = mv^2 / 2s
→
Substituting this expression for F into the work done equation gives: W = (1/2)mv^2
Gravitational potential energy
The energy stored in a mass due to its position in a uniform gravitational field
How do you derive GPE = mgh?
This equation can be therefore derived from the work done: W = Fs
→
Consider a mass, m, lifted through a displacement equal to height, h, the weight of the mass is mg: W = mgs = mgh = GPE
What were the results and conclusions of the α-particle scattering experiment?
- The majority of the α-particles went straight through, showing that an atom is mainly empty space
- Some α-particles deflected through small angles of < 10°, showing there is a dense and positively charged centre
- Only a small number of α-particles deflected straight back at angles of > 90° → the centre of an atom is where all the mass and charge of an atom is concentrated
What are the masses of a proton, neutron and electron?
Both a proton and a neutron have a mass equal to (1)u, while an electron has a mass equal to (0.0005)u
What is the mass or neutron number?
It is the number summing the number of protons and neutrons in the nucleus
What is the atomic or proton number?
It is the number equal to the number of protons; since atoms are neutral, it is also equal to the number of electrons
What does nucleon mean?
A nucleon refers to the particles in the nucleus, protons and neutrons
What is a nuclide?
A nuclide is a specific combination of protons and neutrons in the nucleus
What is an isotope?
An atom of an element that has a different amount of neutrons compared to the other atoms of the same element and hence, they have a different nucleon number
What happens to isotopes over time?
Isotopes have an unstable nucleus due to their imbalance of protons and neutrons and so they will undergo radioactive decay over time to become more s table
What is the stability of an atom determined by?
The stability of an atom is determined by stability of the nucleus or the combination of protons and electrons and it is unaffected by the imbalance of protons or electrons (this affects the charge of an atom)
What are the rules for writing nuclear equations?
The nucleon number and the charge (atomic number) are always conserved
What are alpha particles?
Alpha particles high energy particles made up of 2 protons and 2 neutrons, which is the same as a helium nucleus
What are beta particles?
They are high energy electrons emitted from the nucleus; beta minus is a high energy electron, beta plus is a high energy position
What are gamma rays?
Gamma rays are high energy electromagnetic waves that are released from nuclei that need to lose energy
When are α, β, γ emitted?
- α particles are emitted from nuclei that are too large and contain too many protons and neutrons
- β- particles are emitted by nuclei that have an imbalance between protons and neutrons
- γ particles are emitted by nuclei that have too much or excess energy
How are ionising are α, β, γ?
- An α particle is highly ionising as it has a large charge of (+2)e
- A β particle is moderately ionising due to its charge of (-1)e or (1)e
- A γ ray is less ionising because it has a charge of (0)e
How penetrating are α, β, γ?
- α particles are weakly penetrating and is blocked by a sheet of paper or skin
- β particles are moderately penetrating and can move through a few m in air, but is stopped by a few mm of aluminium
- γ rays are highly penetrating and can penetrate a few m of concrete
Quarks
Quarks are fundamental particles that up hadrons
Fundamental particles
Particles that are not made up of any other particles
Hadrons
Hadrons include any particles made up of quarks
What are the six types of quarks?
Quarks are never by themselves, they are either in a pair or group of three, consisting of:
- Up, down, charge, strange, top or bottom quarks
Leptons
Leptons are the collection of fundamental particles that electrons belong to
What are the six types of leptons?
Electron (e-), electron neutrino (Ve), muon (μ-), muon neutrino (Vμ), tao (τ-), tao neutrino (Vτ)
What are the charges of an electron, muon and tau?
They all have a charge of (-1)e
Neutrinos
Neutrinos are types of leptons, including electron, muon and tau neutrinos, that have a neutral charge and an extremely small/negligible mass
What forces do leptons interact with?
Leptons interact with the weak interaction, electromagnetic forces and gravitational forces, but they do not interact with the strong force
What forces do quarks interact with?
Quarks only interact with the strong force
What are the charges on the six quarks?
- Up, charm and top all have a charge of (+2/3)e
- Down, strange and bottom all have a charge of (-1/3)e
What are protons and neutrinos made up of?
- Protons are formed from two up quarks and one down quark (uud)
- Neutrons are made up one up quark and two down quarks (udd)
Anti-quarks
Anti-quarks are the anti-particles of quarks and are identical except with opposite charges
What are the two types of hadrons?
A hadron may be either a baryon or a meson
Baryons
Baryons are made up of three quarks
Mesons
Mesons are formed from a pair including a quark and an anti-quark
What are the two types of anti-hadrons?
- Anti-baryons - made up of three anti-quarks
- Anti-hadrons - made up of a pair including a quark and an anti-quark (the original quarks that make of the hadron take opposite signs)
By what fundamental force does beta decay occur?
Beta decay happens via the weak interaction
β- decay
β- decay is when a neutron turns into a proton emitting an electron and an anti-electron neutrino or when an up quark turns into a down quark
β+ decay
β+ decay is when a proton turns into a neutron emitting a positron and an electron neutrino because an up quark turns into a down quark
What are the two rules for writing nuclear equations?
- The mass number is conserved
- The atomic number remains the same
Electron neutrino
An electron neutrino is a type of subatomic particle called a lepton with no charge and negligible mass which is emitted from the nucleus
α decay
α decay occurs when an unstable nucleus with too many protons emits an alpha particle from its nucleus and transforms into a different nucleus
What happens to the nucleus during α decay?
- It loses 2 protons - atomic number decreases by 2
- It loses 4 nucleons - the mass number decreases by 4
What happens to the nucleus during β- decay?
- The protons increases by 1 - atomic number increases by 1
- The nucleons remains the same - nucleon number stays constant
What happens to the nucleus during β+ decay?
- The protons decreases by 1 - proton number decreases by 1
- The nucleons stays the same - nucleon number stays constant
What type of energy values does α decay produce?
The energy released in α decay is discrete, meaning α particles always have fixed energies - graph = sharp vertical lines from the x-axis
What type of energy values does β decay produce?
The energy released during β decay is continuous since the energy is shared randomly between the β particle and neutrino - graph = smooth curve
Conventional current
Conventional current is the flow of positive charge carriers from the positive terminal of a cell to the negative terminal - this was the convention used before the discovery of the electron
Electron flow
Electron flow is the flow of negative charge carriers or electrons from the negative terminal to the positive terminal of a cell
How do you measure electric current?
Electric current is measured using an ammeter, which is always connected in series
What is meant by quantisation?
Quantisation refers to how charge carriers only carry discrete amounts of charge
What is the charge on an electron or proton?
One proton or electron carries +/- 1.60 × 10-19 coulombs of charge or 1e
e is known as an elementary charge, charge always comes in multiples of e
What is the equation that relates charge, current and time?
Q = It
Q = charge in C
I = current in A
t = time in s
What is charge?
Charge is the fundamental property of matter that determines how an object will interact in an electric field
Drift speed
It is the average speed of the charge carriers travelling through a conductor
How do you calculate the drift velocity?
I = Anvq
I = current in A
A = cross-sectional area in m^2
n = number density of charge carriers m^-3
v = average drift speed of charge carriers ms^-1
q = charge of each charge carrier in C
A cell or battery
A cell stores chemical energy that it can convert into electrical energy, while a battery is a collection of cells
Potential difference
Potential difference is the energy transferred per unit charge flowing from one to to another
If a component ha a potential difference of 3V, every coulomb of charge passing through the component will transfer 4J of energy to it
State the equation relating potential difference, work and charge:
Potential difference can also be defined as the work done per unit charge:
V = W / Q
V = potential difference in V
W = work done in J
Q = charge in C
Power
Power is the rate at which electrical energy is transferred in a circuit
What is the equation relating electrical power, current and voltage?
The power dissipated or delivered by an electrical device is defined as:
P = VI
State all the equations for electrical power:
- P = VI
- P = I^2R
- P = V^2 / R
Resistance
Resistance is the opposition to electric current, all electrical components have some value of resistance
What effect does resistance have in a circuit?
Resistance determines the amount of charge can flow per unit time, so for a given potential difference:
- A higher resistance reduces the current
- A lower resistance increases the current
Ohm’s law
In words, Ohm’s law states that if a conductor/component has a constant temperature (constant resistance), the current flowing through it is proportional to the potential difference across it, hence:
V = IR
V = potential difference in V
I = current in A
R = resistance in Ω
What is the IV graph for a metallic conductor?
Metallic conductors obey Ohm’s law, current is proportional to potential difference at constant temperature and this is demonstrated by a straight line graph going through the origin
What is the IV graph for a semi-conductor diode?
- When current flow is in the direction of the arrowhead - forward bias - this is shown by a sharp increase in current and a slow increase in potential difference on the right side of the graph
- When current flow is in the opposite direction of the arrowhead - reverse bias - this is shown by a zero reading in current and potential difference
What is a semi-conductor diode?
A diode is a component that only allows electric current to flow in one direction and blocks it in the opposite direction
What is the IV graph for a filament lamp? I DONT KNOW
As current flow increases, the temperature of the filament lamp increases and consequently the resistance too and as resistance opposes current, it begins to increase at a slower rate
Explain the relationship between temperature and resistance:
Temperature and resistance have a relationship where as one increases the other does as well
When the temperature of a conductor increases, the atoms that make it up vibrate faster and these vibrations interfere with the flow of electrons (current) in it, making it harder for them to move smoothly and this causes more collisions and more resistance
What is the formula for resistivity?
R = ρL / A
R = resistance in Ω
ρ = resistivity in Ωm
L = length in m
A = cross-sectional area in m^2
Resistivity
Resistivity is the property of a material describing to extent to which it opposes the flow of electric current
Explain how an LDR works:
A light-dependent resistor or LDR is a non-ohmic component and sensory resistor that when the light intensity incident on it increases, its resistance decreases and vice versa
Explain how a thermistor works:
A thermistor is a non-ohmic component and sensory resistor that when its temperature increases, its resistance decreases and vice versa
How do you measure potential difference?
The potential difference across a component can be measured using a voltmeter that is set up in parallel so it can measure the difference in electrical energy on each side - this is a measure of how much energy is being transferred
Internal resistance
Internal resistance is the resistance all power supplies have between their terminals causing some thermal energy to be dissipated from the power supply itself, therefore, it causes a loss of energy in the power supply, which reduces the available potential difference for the rest of the circuit
Lost volts
This is the voltage lost in the cell or battery due to internal resistance: Lost volts = E.M.F - terminal P.D
What is the equation for calculating internal resistance?
E = I(R + r) = IR + Ir
E = E.M.F in V
I = current in A
R = load resistance in Ω
r = internal resistance in Ω
Kirchhoff’s 1st law
The sum of the currents entering a junction is always equal to the sum of the currents leaving the same junction
What is Kirchhoff’s 1st law a consequence of?
It is a consequence of the law of conservation of charge
How do you tell the difference between the positive and negative terminals of a cell or battery?
The positive terminal is represented by a large line while the negative terminal is shown by a small line
Kirchhoff’s 2nd law
The total E.M.F in a closed circuit is equal to the sum of the potential differences across the components
What is Kirchhoff’s 2nd law a consequence of?
It is a consequence of the law of conservation of energy
Series circuits
A series circuit has one path for current to flow:
- Current is the same through every component
- Potential difference is shared between all components
Parallel circuits
A parallel circuit has multiple paths for current to flow:
- Current is split between the paths
- Potential difference is same across all components
How do you calculate the combined resistance for components in series?
The combined resistance of components in series is equal to the sum of the individual resistances
How do you calculate the combined resistance for components in parallel?
The reciprocal of the combined resistance is the sum of the reciprocals of the individual resistances
Provide the derivation for resistors in series:
Provide the derivation for resistors in parallel:
What are the thee main purposes of potential dividers?
- To provide a variable potential difference
- To enable a specific potential difference to be chosen
- To split the potential difference of a power source between two or more components
- They are used widely in volume controls and sensory circuits using LDRs and thermistors
How do you calculate the output voltage in a potential divider circuit?
It is equal to the ratio of between the two components, which is equal to the ratio of the resistances of the resistors:
V-out = V-in[ R2 / (R1 + R2) ]
The resistance R2 on the numerator of the fraction is always the resistance of the component that V-out is connected to
Potentiometer
A potentiometer is a variable resister connected as a potentiometer to give a continuously variable output voltage, it allows the potential differences in different parts of the circuit to be compared
Galvanometer
A galvanometer is a type of sensitive ammeter used to detect electric current, it is used in a potentiometer to measure E.M.F between two points in a circuit
How does a galvanometer work?
The arrow of a galvanometer represents a needle, which deflects depending on the amount of current passing through: When the arrow is facing directly upward, there is no current and this is known as null deflection
When does a galvanometer have a P.D of zero?
When the potential on one side equals the potential on the other side, this is at the position at which it is connected on the wire (which varies with the sliding contact) gives a P.D equal to the E.M.F of the cell connected to the galvanometer, this cell should be connected such that its potential opposes the potential on the wire - the positive terminal of the power supply faces the positive terminal of the cell
What happens when the sliding contact of a potentiometer moves?
You add or remove resistance from/to the external circuit. This changes the potential drop across X and Y
How is work done related to energy?
The total work done is equal to the total energy transferred
Provide the derivation for EK:
Provide the derivation for GPE:
