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AS Physics, Waves, Mechanics, Electricity, Materials, Electric and…

- - - - A line that represents points where a wave is in phase
    - - Waves that have the same frequency and phase difference
    - - Difference in distance of two waves from where they meet
    - - The vector sum of two meeting waves' displacements
    - - Is either constructive or destructive as a result of superposition
    - - The stage a point is at on a complete wave cycle
  - - - Difference in distance travelled by two waves from where they meet to their sources
      - Measured in multiples of wavelength
    - - Measured in the angle between them (° or rad)
      - Difference of stages two points are at on a wave cycle
    - - Destructive: pi or (n + 1/2)λ
      - Constructive: 2pi or nλ
  - - - T for string tension
      - μ for mass per unit length
- - - - Focal point: Where rays of light intersect / are brought to a focus at
      - Focal length: Distance between centre of lens and focal point
    - - Concave / Diverging lens
        
        Parallel rays appear to be brought / diverge from focal point
      - Convex / Converging lens
        
        Parallel rays are brought / converge to focal point
    - - The ability for a lens to refract light
      - P = 1/f
        
        P is inversely proportional to f
        
        P for Power in (D)
        
        f for focal length
      - If multiple lenses are used in series (compound lens), total power is the sum of individual powers
      - With regards to distance: 1/f = 1/u + 1/v
        
        u for object distance from lens
        
        v for image distance from lens
    - - Image height / Object height
      - Lens distance to image / Lens distance to object
    - - Real images
        
        Form on a screen
        
        Created by intersecting rays from diverging or converging
        
        Diverging: Object is at any distance
        
        Converging: Object is less than focal length away
        
        Inverted
      - Virtual images
        
        Cannot be formed on a screen
        
        Created by diverging rays
        
        Upright
- - - - Increases as the slit width narrows to the wavelength
      - More than wavelength - no more diffraction
    - - Points of a wavefront are sources of wavelets
      - Wavelets can interfere with each other constructively and destructively
    - - When a monochromatic light beam passes through a grating, light and dark fringes form due to diffraction
      - dsin0 = nλ
        
        d for spacing between slits (m)
        
        1/ No. of slits per (m)
        
        0 for angle from central maxima
        
        n for order of maxima
        
        λ for wavelength
- - - - EM radiation travels as quanta of energy or particles known as photons
    - - The energy of a photon
      - Φ for work function
        
        Minimum energy requirement for emitting electrons
      - ½mv^2 for max. kinetic energy
        
        Remaining energy transferred after work function releases electrons
      - f for threshold frequency
        
        Minimum frequency requirement for emitting electrons
      - c for speed of light
      - h for Planck's constant
  - - - Increasing intensity increases rate of electron emission
      - One electron absorbs one photon (energy), and is emitted spontaneously
      - Energy increases with frequency given that it is above the threshold
    - - Any frequency will cause electron emission
      - Increasing intensity increases energy
      - Energy absorbed by electrons gradually increases
  - - - Energy requirement equals to the energy level difference
      - Absorption can be due to temperature, absorbing photons, collisions with other atoms / ionisation
- - - - Object remains at rest or constant velocity unless acted on by a RESULTANT force
      - No resultant force if opposite forces are equal to each other
    - - Two ways to describe
        
        Resultant force is directly proportional to acceleration
        
        When a resultant force acts on an object, it accelerates at the force's direction
      - F = ma
    - - Moving objects can have a resultant force acting due to:
        
        A driving / thrust force produced by them
        
        Their own weight (if they are falling)
        
        Friction and drag forces
      - With increasing acceleration, the driving force increases, but so do drag forces
      - Those forces will equal each other to the point of no resultant force
      - A maximum terminal velocity would be reached
  - - - Exactly two objects involved
      - Same type of force
      - Same magnitude
      - Same line of direction
    - - A foot exerts a force on the ground. The ground exerts the same force on the foot for it to step forward
  - - - Closed system - no external forces or external energy transfer
    - - Understand that two objects exert equal and opposite forces on each other
      - One object gains momentum, the other loses it
      - Magnitudes of forces before and after
        
        Before: F
        
        After: -F
      - Acceleration is equal for objects of equal mass
        
        One object accelerates from 0 to v
        
        The other object decelerates from v to 0
- - - - Wider base - more stable
      - Thinner base - less stable
- - - - If not in same direction, use sin0 or cos0
  - - - Energy stored in a moving object
      - Changes with velocity / acceleration
        
        Acceleration --> Increases
        
        Deceleration --> Decreases
      - KE = 1/2 mv^2
    - - Energy stored when in a gravitational field
      - Changes with height
        
        Higher --> Increases
        
        Lower --> Decreases
        
        On ground = 0
      - GPE = mgh
    - - Energy cannot be created or destroyed, only transferred
      - There is a link between KE and GPE - one can be transferred to the other
        
        Objects in freefall
        
        Moving pendulum
      - Drag forces may have effects on the total energy in the system
- - - - Flat line: Stationary
      - Straight diagonal line: Constant speed
      - Positive slope: Moving forward
      - Negative slope: Moving backwards
      - Steeping curve: Acceleration
      - Flattening curve: Deceleration
    - - Flat line: Constant speed
      - Positive slope: Acceleration
      - Negative slope: Deceleration
      - Area underneath: Displacement
      - Below x axis: Moving in the opposite direction
    - - Flat line above x axis: Constant acceleration
      - Flat line on x axis: Constant speed
      - Flat line below x axis: Constant acceleration in the opposite direction
      - Area underneath: Speed
  - - - Speed
      - Mass
      - Distance
    - - Weight
      - Displacement
      - Velocity
  - - - Use vertical component
      - Refer to v^2 = u^2 + 2as
    - - Use vertical component
      - Refer to 2 x (v = u + at)
    - - Use horizontal component
      - Refer to s = vt
- - - - Q for charge (C)
      - t for time (s)
    - - Conventional: + to -
      - Electron: - to +
  - - - W for work done (J)
      - Q for charge (C)
  - - - V = IR
      - Current is directly proportional to p.d. for a CONSTANT TEMPERATURE
      - Obeyed by a fixed resistor
    - - R(t) = R(1) + R(2)...
      - V(t) = V(1) + V(2), so IR(t) = IR(1) + IR(2), but current is constant
    - - 1/R(t) = 1/R(1) + 1/R(2)...
      - I(t) = I(1) + I(2), so V/R(t) = V/R(1) + V/R(2), but p.d. is constant
  - - - Sum of currents entering junction = Sum of currents leaving junction
      - Charge is being conserved
        
        Q(t) = Q(1) + Q(2)...
      - Series and Parallel
        
        For series: Same at every point
        
        I(t) = I(1) = I(2)...
        
        For parallel: Total split between branches
        
        I(t) = I(1) + I(2)...
    - - Sum of e.m.f.s in a closed loop = Sum of p.d.s in that closed loop
        
        Closed loop represents series circuit
      - Energy is being conserved
      - Series and Parallel
        
        For series: e.m.f. is split across components
        
        E = V(1) + V(2)...
        
        For parallel: p.d. for each closed loop is equal to e.m.f.
        
        E = V(1) = V(2)...
  - - - As V = IR, P = I^2R
      - As I = V/R, P = V^2 / R
      - As P = W/t, then W = IVt
  - - - Straight line - resistance is constant and Ohm's law is followed
    - - Decreasing gradient - temperature increases with current, so will resistance, hence current increases much slower over time
    - - Increasing gradient - temperature increases with current, but resistance falls, so current increases at a faster rate
    - - Current is zero on one side, but very high on the other
        
        Diodes let current flow in ONE DIRECTION ONLY
        
        Forward bias - of low resistance, current can flow
        
        Reverse bias - of very high resistance, no current can flow
- - - - R is directly proportional to p (resistivity) & l (length of wire)
        
        Since V = IR, for a constant current V must also increase with length
      - R is inversely proportional to A (cross sectional area of wire)
    - - Ions reduce the flow of charge
      - Kinetic energy of electrons is transferred as heat, rate of flow decreases
  - - - v for drift velocity
        
        Drift velocity - mean velocity of charge carriers, e.g. free electrons
      - I for current
      - n for charge carrier density
        
        Charge carrier density - number of charge carriers per unit volume
      - A for cross sectional area
      - q for charge
    - - v is inversely proportional to n, A & q
      - v is directly proportional to I
    - - Insulators have high resistivity - very little or no charge carriers
      - Conductors have low resistivity - lots of charge carriers including free electrons
      - Semiconductors have varying resistivity - normally have low number of delocalised electrons, but number increases with temperature / intensity
  - - - Potentiometers and variable resistors are responsible for this variance
        
        Potentiometers
        
        Can be set from 0V-Vin
        
        V is measured even w/o current
        
        Variable resistors
        
        Cannot set to 0V with other components around
        
        Needs current for V to be measured
    - - Larger R: Greater share of Vin
      - Smaller R: Smaller share of Vin
    - - Their voltage increases with resistance, so a resistor's voltage is of a lower share then
      - Their voltage decreases with resistance, so a resistor's voltage is of a higher share then
- - - - Voltage is lost from the EMF as a result - known as lost volts
  - - - Electrons collide with vibrating ions
      - Kinetic energy is transferred as thermal energy by the electrons
      - Temperature increases, so vibrations and their amplitude increase
      - The rate of collisions between electrons and ions increase
      - Because the flow of current is resisted and overall current decreases, obviously resistance increases
    - - When temperature increases, electrons gain more energy to be emitted from shells in ions
      - The no. of charge carriers increases, so current increases, which reduces resistance
  - - - When light intensity increases, more light energy is provided for electrons to be emitted from ions
      - The no. of charge carriers increases, so current increases, which reduces resistance
- - - - An object stops falling when upthrust (and viscous drag) equals its weight
    - - Volume of object = Volume of displaced fluid
      - Weight of object ≠ Weight of displaced fluid
    - - p for fluid density
      - V for object volume
  - - - Where:
        
        r for radius
        
        v for velocity
        
        η for viscosity coefficient (how well the fluid resists flowing)
      - Only applicable for:
        
        Small, spherical objects
        
        Low velocity motion
        
        Laminar flow
    - - Falling: W = U + D
        
        Drag is in direction of upthrust
      - Rising: W = U - D
        
        Drag is in direction of weight
      - Can be expressed by:
    - - Laminar flow has layers with same direction and no mixing
      - Turbulent flow has layers with constantly changing direction and mixing
    - - For a gas - increases with it
      - For a liquid - decreases with it
- - - - F for force applied
      - Δx for extension
      - k for spring constant (Nm^-1) - measure of stiffness
  - - - C: Yield point
        
        Point where material shows increasing extension for little to no force applied
      - Elastic deformation
        
        Before B
        
        Material returns to original shape from deformation once force is removed
      - B: Elastic limit
        
        Point before elastic deformation stops being seen
      - Plastic deformation
        
        After B
        
        Material retains deformed shape once force is removed
      - A: Limit of proportionality
        
        Point where Hooke's law stops being obeyed
  - - - 1/2 FΔx
      - 1/2 kΔx^2
  - - - Stress - force applied per unit area in Pa
        
        Stress = Force / Area
      - Strain - extension per unit length (no dimensions)
        
        Strain = Extrension / Length
- - - - Electric Field Strength = Force / Charge
      - Force per unit charge acting on a positive charge
      - Direction
        
        Towards a positive charge
        
        Away from a negative charge
    - - Field Strength = kQ / r^2
      - Field produced is radial
    - - Field strength = V / d
      - Field produced is uniform
  - - - Proportional to product of charges
      - Inversely proportional to square of separation
    - - Negative due to opposite charges / attraction
      - Positive due to same charges / repulsion
  - - - Decreases the further you are from a positive charge
      - Increases the further you are from a negative charge
    - - If potential gradient changes more rapidly with displacement, field strength is stronger
      - If potential gradient changes more gradually with displacement, field strength is weaker
    - - Work done to move a positive test charge:
        
        Away from a negative charge
        
        Near to a positive charge
    - - For positive charge, V is positive and increases as r decreases
        
        More work is done to overcome repulsion
      - For negative charge, V is negative and decreases as r decreases
        
        Less work is needed since the attractive force becomes stronger