Physics Chapter: Forces and Energy
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Questions and Answers

What do you call quantities that have both magnitude and direction?

  • Scalars
  • Constants
  • Vectors (correct)
  • Coefficients

    • How is weight defined scientifically?

  • The force due to gravity acting on an object (correct)
  • The total mass of an object irrespective of gravity
  • The gravitational pull experienced only in a vacuum
  • The mass of an object divided by gravitational field strength

    • Which equation is used to calculate gravitational potential energy?

  • GPE = mgh (correct)
  • GPE = mg
  • GPE = mg^2
  • GPE = Fd

    • What must be done to keep an object stationary in the presence of gravitational force?

    <p>Apply an upward force equal to its weight</p> Signup and view all the answers

    What is the relationship between work done and force at an angle?

    <p>Only the component of force parallel to the distance contributes to work done</p> Signup and view all the answers

    Which of the following statements is true under Newton's First Law?

    <p>An object will remain in motion unless a resultant force acts on it</p> Signup and view all the answers

    How is power defined in terms of force and velocity?

    <p>Power = F * v</p> Signup and view all the answers

    To calculate the resultant force of two forces acting at right angles to each other, which mathematical principle is applied?

    <p>Pythagorean theorem</p> Signup and view all the answers

    What does Hooke's law state about the relationship between force and extension for elastic materials?

    <p>F = kx</p> Signup and view all the answers

    What is the unit of the spring constant k?

    <p>Newtons per meter (N/m)</p> Signup and view all the answers

    What does stress measure in a material?

    <p>The force divided by the area over which it is applied</p> Signup and view all the answers

    What occurs when a material reaches its elastic limit?

    <p>It undergoes plastic deformation and does not return to original shape.</p> Signup and view all the answers

    What is the equation used to calculate voltage?

    <p>V = E/Q</p> Signup and view all the answers

    What does Ohm's Law state about the relationship between voltage, current, and resistance?

    <p>V = IR</p> Signup and view all the answers

    How is the total resistance calculated in a series circuit?

    <p>By summing all individual resistances</p> Signup and view all the answers

    What happens to the current in a parallel circuit when more branches are added?

    <p>The total current increases</p> Signup and view all the answers

    What is the main characteristic of a thermistor?

    <p>Its resistance decreases with increasing temperature</p> Signup and view all the answers

    What does resistivity measure in materials?

    <p>Resistance of a 1m cube of a material</p> Signup and view all the answers

    In a complete circuit, what is the primary role of electrons?

    <p>To transfer energy from a source to a component</p> Signup and view all the answers

    What defines the ultimate tensile stress of a material?

    <p>The maximum stress the material can withstand before failure</p> Signup and view all the answers

    What does a diode do in an electronic circuit?

    <p>Restricts current flow to one direction</p> Signup and view all the answers

    What is the significance of the area under a force-extension graph for a spring?

    <p>It represents the work done on the spring</p> Signup and view all the answers

    What does Newton's third law state about forces acting on two objects?

    <p>For every action force, there is an equal and opposite reaction force.</p> Signup and view all the answers

    How is the component of weight acting parallel to a slope calculated?

    <p>mgsinθ</p> Signup and view all the answers

    What must be true for an object to remain stationary on a slope?

    <p>The net force acting on it must equal zero.</p> Signup and view all the answers

    What is the relationship between gravitational potential energy at the top of a slope and kinetic energy at the bottom of a slope in the absence of friction?

    <p>Potential energy equals kinetic energy.</p> Signup and view all the answers

    What constitutes momentum in physics?

    <p>Mass multiplied by velocity.</p> Signup and view all the answers

    What happens to an object's momentum in a collision?

    <p>Momentum is conserved.</p> Signup and view all the answers

    What is true about the impulse experienced by an object?

    <p>Impulse is equal to the change in momentum.</p> Signup and view all the answers

    In the context of moments, under what condition does an object remain in equilibrium?

    <p>Sum of clockwise moments equals the sum of anticlockwise moments.</p> Signup and view all the answers

    What does Stokes' law help to calculate?

    <p>The magnitude of drag acting on a sphere in a fluid.</p> Signup and view all the answers

    Under which condition does upthrust act on an object submerged in a fluid?

    <p>It is equal to the weight of the fluid displaced by the object.</p> Signup and view all the answers

    When launching an object at an angle, what should be done to analyze its motion effectively?

    <p>Resolve the initial velocity into vertical and horizontal components.</p> Signup and view all the answers

    What is the principle underlying the concept of density?

    <p>Density is mass divided by volume.</p> Signup and view all the answers

    What does the equation for calculating moments not account for?

    <p>The parallel distance between force and pivot.</p> Signup and view all the answers

    What describes a couple in terms of its effects on an object?

    <p>It creates a resultant moment causing rotation without acceleration.</p> Signup and view all the answers

    What is the relationship between RMS voltage and peak voltage?

    <p>RMS voltage is peak voltage divided by the square root of 2.</p> Signup and view all the answers

    How does increasing load resistance affect terminal PD and current?

    <p>Terminal PD increases while current decreases.</p> Signup and view all the answers

    What defines the behavior of electrons in semiconductors?

    <p>Electrons can move only when they have enough energy to reach the conduction band.</p> Signup and view all the answers

    What is the formula for calculating drift velocity?

    <p>v = I / (n * A * e)</p> Signup and view all the answers

    What happens to light waves when they move from one medium to another?

    <p>They change speed and wavelength.</p> Signup and view all the answers

    What does Snell's Law describe?

    <p>The angle at which light bends when moving between different media.</p> Signup and view all the answers

    What occurs during total internal reflection?

    <p>Light reflects entirely back into the denser medium.</p> Signup and view all the answers

    How is the frequency of harmonics on a string defined?

    <p>f = (1/2L) * √(T/μ)</p> Signup and view all the answers

    What is a characteristic of stationary waves?

    <p>Antinodes have maximum amplitude.</p> Signup and view all the answers

    What does the Young double-slit equation determine?

    <p>The fringe spacing in an interference pattern.</p> Signup and view all the answers

    What is modal dispersion in optic fibers?

    <p>The varying time taken for light rays traveling different paths.</p> Signup and view all the answers

    What happens to amplitude during wave interference?

    <p>It can increase or decrease based on constructive or destructive interference.</p> Signup and view all the answers

    What is the critical angle in refraction?

    <p>The angle of incidence leading to total internal reflection.</p> Signup and view all the answers

    What is the significance of number density in semiconductors?

    <p>It indicates the number of charge carriers per unit volume.</p> Signup and view all the answers

    What is the process by which an electron transitions from a higher energy level to a lower energy level?

    <p>De-excitation</p> Signup and view all the answers

    What determines the energy of an emitted photon when an electron transitions between energy levels?

    <p>The frequency of the photon</p> Signup and view all the answers

    What type of spectrum illustrates the wavelengths of photons absorbed by a gas or plasma?

    <p>Absorption spectrum</p> Signup and view all the answers

    Which of the following best describes the photoelectric effect?

    <p>Electrons are emitted from a metal surface when illuminated by light.</p> Signup and view all the answers

    What does the term 'threshold frequency' refer to in the context of the photoelectric effect?

    <p>The minimum frequency of light needed to liberate an electron</p> Signup and view all the answers

    In particle-wave duality, what is the De Broglie wavelength of a particle defined as?

    <p>$h/p$</p> Signup and view all the answers

    What kind of error is caused by viewing a measurement from an angle?

    <p>Parallax error</p> Signup and view all the answers

    What is the relationship between percentage uncertainty and multiplying values?

    <p>Add all percentage uncertainties regardless of the operation.</p> Signup and view all the answers

    What does a straight-line graph in physics experiments aim to determine?

    <p>The gradient and relationship between variables</p> Signup and view all the answers

    In the context of Kepler's laws, what does the gradient of the log graph reveal?

    <p>The relationship between orbital period and distance from the sun</p> Signup and view all the answers

    How does the uncertainty of a measurement relate to the resolution of the measuring tool?

    <p>It is equal when the tool is properly aligned.</p> Signup and view all the answers

    What is the formula for calculating the kinetic energy of emitted electrons in the photoelectric effect?

    <p>KE = hf - Φ</p> Signup and view all the answers

    In log graphs, what does the manipulation of log identities help establish?

    <p>The proportional relationship between variables.</p> Signup and view all the answers

    What does the work function represent in the photoelectric effect?

    <p>The minimum energy required to liberate an electron</p> Signup and view all the answers

    Study Notes

    Representing Forces

    • Forces can be represented using vectors, which are arrows that show both the direction and magnitude of the force.
    • When two forces act on an object, we can find the resultant force by adding the vectors.
    • If forces act in opposite directions, one is considered negative.
    • The resultant force is found by adding the vectors, taking into account the positive and negative direction.
    • To find the resultant force of vectors at right angles, use Pythagoras theorem.
    • Use trigonometry (SOH CAH TOA) to find angles.
    • A scalar quantity has magnitude but no direction.
    • Examples of scalar quantities include speed, distance, mass, and energy.
    • Examples of vector quantities include velocity, displacement, force, weight, and momentum.

    Weight, Work Done, and Gravitational Potential Energy

    • Weight is the force due to gravity acting on an object.
    • Weight can be calculated using the equation weight = mass * gravitational field strength (W = mg).
    • On Earth, the gravitational field strength is approximately 9.8 N/kg.
    • To keep an object stationary, an upward force equal to the object's weight needs to be applied.
    • To lift an object at a constant speed, an upward force equal to the object's weight needs to be applied.
    • Work done is calculated using the equation work done = force * distance moved (W = Fs).
    • When an object is lifted, the work done equals the gain in gravitational potential energy.
    • The equation for gravitational potential energy can be written as GPE = mgh.
    • This is the same equation as the one for work done when lifting the object, where force equals weight.
    • Work done requires the force and distance moved to be parallel.
    • If the force is at an angle, resolve the force into components parallel and perpendicular to the distance traveled.
    • The component parallel to the distance is used to calculate work done.
    • The equation for work done can be adjusted to account for force at an angle: W = Fscosθ.

    Power

    • Power can be calculated using the equation *power = force * velocity * (P = Fv).
    • Power is also known as power developed and represents the rate of work done.

    Newton's Laws of Motion

    • Newton's First Law: When there is no resultant force acting on an object, its motion remains constant (no change in velocity). This can occur because there are no forces acting on the object, or because the forces are balanced.
    • Newton's Second Law: Unbalanced forces result in a resultant force. This resultant force is equal to the mass of the object multiplied by its acceleration (F = ma). Only one of these conditions can be true at a time. Either there is no resultant force, or there is a resultant force.
    • Newton's Third Law: This law states that for every action force, there is an equal and opposite reaction force. This is not referring to balanced forces, but rather to the perspective of forces acting upon two objects.

    Forces on an Object on a Slope

    • If an object is placed on a slope, its weight (mg) acts downwards.
    • The reaction force of the slope acts perpendicular to the slope, and is calculated as reaction force = mgcosθ.
    • The component of weight acting parallel to the slope is mg sinθ.
    • This component always pulls the object down the slope.
    • If the object is stationary or moving at a constant speed, there must be another force equal to mg sinθ acting upwards to balance the forces. This force is often friction.
    • To find the resultant force on an object on a slope, sum all forces in one direction and subtract all forces acting in the opposite direction.
    • Use F = ma to calculate the acceleration of the object.
    • The height of the slope can be used to calculate changes in gravitational potential energy and kinetic energy.

    Energy Changes on a Slope

    • If there are no frictional forces, the total energy of the object remains constant.
    • The gravitational potential energy at the top of the slope will be equal to the kinetic energy at the bottom of the slope.
    • If there are frictional forces, energy will be lost due to work done by friction.
    • The work done by friction can be used to find the average frictional force.
    • Be careful to use the distance traveled as the distance moved in the work done equation, not the height.

    Equations of Motion

    • If an object is accelerating, use one of the equations of motion to analyze its movement.
    • The equations of motion relate the following variables:
      • s - displacement
      • u - initial velocity
      • v - final velocity
      • a - acceleration
      • t - time
    • If an object is moving in one direction, all values can be positive, even if the object is moving downwards.
    • Watch out for acceleration, which can be negative for objects decelerating.

    Objects Thrown Upwards

    • When an object is thrown upwards and returns to its original position, the total displacement is technically zero.
    • To simplify calculations, split the problem into two parts: from the start to the apex (where v = 0), and from the apex back to the start.
    • Double the time taken for the upward journey to find the total time taken for the round trip.

    Objects Thrown Horizontally

    • For objects launched horizontally off a cliff, split the motion into vertical and horizontal components.
    • Use the equations of motion for vertical movement:
      • u = 0 (initial vertical speed is zero)
      • a = g (acceleration due to gravity)
      • s = height of the cliff
    • The horizontal velocity remains constant.
    • Use the equation speed = distance / time for horizontal motion.

    Oblique Launch

    • Resolve the initial velocity of an object launched at an angle into vertical and horizontal components.
    • Use the equations of motion for vertical movement.
    • Use speed = distance / time for horizontal movement.

    Momentum

    • Momentum is a measure of an object's motion.
    • It is calculated using the equation momentum = mass * velocity (p = mv).
    • The unit of momentum is kg m/s.
    • Momentum is a vector.
    • Objects moving to the left will have negative momentum.
    • In a collision, the total momentum before the collision is equal to the total momentum after the collision.
    • Be careful with signs when calculating momentum.

    Impulse and Change of Momentum

    • Impulse is the change in momentum.
    • It can be calculated using the equation impulse = force * time (Ft)
    • The unit of impulse is Ns (Newton seconds).
    • Impulse can also be calculated as the area under a force-time graph.
    • The impulse is the momentum gained by a stationary object.

    Force and Momentum

    • Force is related to the rate of change of momentum, F = Δp/Δt.
    • When a fluid exerts force on an object, the force can be calculated using the equation *F = ρav².
    • This equation represents the momentum carried per second by the fluid.

    Moments

    • A moment, or torque, is a turning force about a pivot point.
    • The equation for moment is moment = force * perpendicular distance to the pivot (M = Fd).
    • The unit of moment is Nm (Newton meters).
    • Moments are not the same as work done, as force and distance need to be perpendicular, not parallel.
    • The principle of moments states that for an object to be in equilibrium, the sum of clockwise moments must equal the sum of anticlockwise moments.
    • Moments can be taken about any point, even without a physical pivot.

    Couples

    • A couple is a pair of forces acting in opposite directions on an object, causing a resultant moment but no resultant force.
    • A couple causes an object to rotate but does not cause it to accelerate.
    • An object will topple over if its centre of gravity is moved past the pivot vertically.

    Upthrust

    • Upthrust is the upward force exerted by a fluid on an object.
    • It is equal to the weight of the fluid displaced by the object.
    • Upthrust can be calculated using the equation upthrust = weight of displaced fluid = ρVg.
    • When calculating the resultant force on an object in a fluid, consider both upthrust and drag.

    Stokes Law

    • Stokes law provides the magnitude of drag acting on a sphere moving through a fluid: F = 6πηRv.
    • This equation assumes laminar flow, where the fluid is disturbed as little as possible.
    • Viscosity is a property of fluids that measures their resistance to flow.

    Density

    • Density is calculated as density = mass / volume (ρ = m/V)
    • The unit of density is kg/m³.
    • For mixtures of materials, remember that the total mass of the mixture is equal to the sum of the masses of each component.

    Elasticity

    • Forces can deform objects.
    • Hooke's law describes the relationship between force and extension for elastic materials: F = kx.
    • The spring constant k measures the stiffness of the material and is measured in N/m.
    • Elastic materials return to their original shape after the force is removed.
    • The area under a force-extension graph represents the work done on the spring and the elastic potential energy stored within the spring.
    • The spring constant of two or more springs connected in series is the reciprocal of the sum of the reciprocals of the individual spring constants.
    • The spring constant of two or more springs connected in parallel is the sum of the individual spring constants.

    Stress and Strain

    • Stress is the force per unit area applied to an object.
    • It is measured in Pascals (Pa) or N/m².
    • Strain is the ratio of the extension to the original length of the object.
    • Strain has no unit.
    • Young's modulus (E) is the ratio of stress to strain for an elastic material.
    • It is measured in Pascals (Pa) or N/m².
    • It can be calculated using the equation E = σ/ε.

    Yield Point and Ultimate Tensile Stress

    • The limit of proportionality is the point on a stress-strain graph where the relationship between stress and strain ceases to be proportional.
    • After the limit of proportionality, the elastic limit is reached.
    • If the force is removed after exceeding the elastic limit, the material will not return to its original shape, and will undergo plastic deformation.
    • The ultimate tensile stress is the maximum stress a material can withstand before failure.

    Electricity

    • Electricity is the flow of charge.
    • The flow of charge is commonly carried by electrons.
    • Electrons transfer energy from a source, such as a battery or cell, to a component in a circuit.
    • When connected in a complete circuit, a battery converts its chemical potential energy into electrical energy, causing electrons to move through the wires.
    • This flow of charge is called current.
    • Current is conventionally said to flow from the positive terminal of the battery to the negative terminal.
    • The electrons lose their energy as they pass through components, such as a light bulb, converting it to other forms of energy such as heat and light.
    • The electrons are pushed back around the circuit by the ones behind them, and replenish their energy from the battery.

    Voltage

    • Voltage, or potential difference (PD), is the energy transferred per coulomb of charge.
    • It is measured in volts (V).
    • A voltage of 1 V means that 1 J of energy is given to every 1 C of charge that passes through the component.
    • Voltage is measured with a voltmeter, which is connected in parallel with the component whose voltage is being measured.
    • The voltage across a battery is the same as the voltage provided to the entire circuit.
    • The voltage across a component is the amount of energy lost by each coulomb of charge as it passes through that component.
    • The equation for voltage is V = E/Q.

    Current

    • Current is the rate of flow of charge: I = Q/t, where I is current, Q is charge, and t is time.
    • It is measured in Amperes (A).

    Current and Resistance

    • Current (I) is measured in Amperes (A) using an ammeter placed in series with the component.
    • Resistance (R) is the opposition to the flow of charge or current.
    • Components in a circuit have resistance, necessary for functioning.
    • A bulb's resistance converts energy into light, while a resistor produces heat.
    • Ohm's Law: V = IR, where V is potential difference, I is current, and R is resistance.
    • Potential difference (PD) and current are directly proportional for a resistor, resulting in a straight-line graph.
    • The gradient of the IV graph for a resistor is constant, indicating constant resistance.
    • A resistor with a steeper gradient has lower resistance, allowing more current flow per volt.
    • The resistance of a metal filament in a bulb changes with increasing PD and current, making it non-ohmic.
    • Metals have a lattice of ions surrounded by delocalized electrons that collide with ions, creating resistance and heat.
    • A diode only allows current to flow in one direction, exhibiting high resistance in one direction and low in the other.
    • An LED is a light-emitting diode, similar to a diode but producing light.
    • A superconductor has zero resistance, usually achieved at low temperatures.

    Resistivity

    • Resistivity (ρ) is the resistance of a 1m cube of a material, measured in ohm meters.
    • The resistance of a wire varies with its length (L) and cross-sectional area (A), following the equation: R = ρL/A
    • Resistivity can be determined from the gradient of a graph of resistance against length.

    Series Circuits

    • In a series circuit, the total PD is shared between components.
    • The current is the same for all components.
    • The total resistance is the sum of all resistances.
    • Kirchhoff's Second Law: The sum of electromotive forces (EMFs) equals the sum of PD drops in a closed loop.
    • A potential divider circuit distributes the total PD across components.
    • Higher resistance leads to a greater share of the total PD.

    Parallel Circuits

    • In a parallel circuit, the PD is the same for all branches.
    • The current is shared between branches.
    • The total resistance decreases as more resistors are added in parallel.
    • Kirchhoff's First Law: Current is conserved at any junction.

    Thermistors and Light-Dependent Resistors (LDRs)

    • A thermistor's resistance decreases with increasing temperature.
    • An LDR's resistance decreases with increasing light intensity.

    Power

    • Power (P) is the rate of energy transfer, calculated as P = VI, where V is potential difference and I is current.

    Alternating Current (AC)

    • AC is used to transmit electricity over long distances.
    • Transformers convert AC voltage, stepping up the voltage and reducing the current.
    • The neutral wire in mains electricity has a potential of 0V, while the live wire varies between +325V and -325V.
    • Peak voltage is 325V, and peak-to-peak voltage is 650V.
    • RMS values are used to convert AC to DC equivalent.
    • RMS voltage (VRMS) = Peak Voltage/
    • RMS current (IRMS) = Peak Current/
    • Average power is half the peak power.

    Internal Resistance

    • Batteries and cells have internal resistance (r).
    • Terminal PD is the voltage available to the circuit.
    • EMF (ε) is the total PD provided by the battery.
    • EMF = Terminal PD + (I * r)
    • Increasing the load resistance decreases the current and increases the terminal PD.
    • The gradient of a graph of terminal PD against current equals the internal resistance.
    • The y-intercept of the graph equals the EMF.

    Semiconductors

    • Semiconductors have electrons that are only free to move when provided with enough energy to transition to the conduction band.
    • Number density represents the number of charge carriers per cubic meter, varying between conductors, semiconductors, and insulators.

    Drift Velocity

    • Drift velocity is the speed of electrons flowing through a wire, calculated using: I = nAve, where I is current, A is area, n is charge carrier density, e is electron charge, and v is drift velocity.

    Waves

    • Waves transfer energy without transferring matter.
    • Longitudinal waves oscillate parallel to the direction of energy transfer, creating compressions and rarefactions.
    • Transverse waves oscillate perpendicular to the direction of energy transfer.
    • Amplitude is the maximum displacement from equilibrium.
    • Wavelength (λ) is the distance of one complete wave cycle.
    • Time period (T) is the time for one complete wave to pass a point.
    • Frequency (f) is the number of waves passing a point per second, calculated as: f = 1/T
    • The wave equation: V = fλ, where V is wave speed, f is frequency, and λ is wavelength.
    • The intensity of a wave is proportional to its amplitude squared.

    Refraction

    • Light waves change speed and wavelength when moving from one medium to another.
    • Refraction is the bending of light as it passes from one medium to another at an angle.
    • The angle of refraction is smaller than the angle of incidence if light slows down.
    • Refractive index (n) is the ratio of the speed of light in a vacuum to the speed of light in the medium.
    • Snell's Law: n1 sin θ1 = n2 sin θ2, where n1 and n2 are refractive indices, and θ1 and θ2 are angles of incidence and refraction, respectively.
    • The critical angle is the angle of incidence that results in an angle of refraction of 90 degrees.
    • Total internal reflection occurs when the angle of incidence exceeds the critical angle, reflecting all light back into the denser medium.

    Optic Fibers

    • Optic fibers use total internal reflection to transmit light.
    • Modal dispersion occurs due to light rays taking different paths and times to travel through the fiber, resulting in pulse broadening.
    • Solutions to modal dispersion include using thin fibers, repeaters, and graded index fibers.

    Polarization

    • Unpolarized light oscillates in all orientations.
    • A polarizing filter only allows waves of a specific orientation to pass through, reducing light intensity by half.
    • Two polarizing filters at 90 degrees will block all light.

    Phase Difference

    • Two points on a wave are in phase if they are doing the same thing at the same time.
    • Their phase difference is 0 degrees or 2π radians.
    • Points on opposite sides of a wave are out of phase or in antiphase, with a phase difference of 180 degrees or π radians.

    Phase Difference

    • Two points on a wave are a quarter of a wavelength out of phase: 90° or π/2 radians phase difference.
    • Phase difference can be calculated as a fraction of a whole cycle: (distance between points / wavelength) * 360° or (time difference / time period) * 2π.

    Superposition and Stationary Waves

    • When two waves with identical frequency and wavelength, traveling in opposite directions, meet, they superpose.
    • A stationary wave forms: no energy is transferred.
    • Nodes: points of destructive interference, where amplitude is zero.
    • Antinodes: points of constructive interference, where amplitude is a maximum.

    Stationary Waves on a String

    • First Harmonic (Fundamental): one loop, one antinode, nodes at both ends, L = λ/2.
    • Second Harmonic: two loops, two antinodes, L = λ.
    • Third Harmonic: three loops, three antinodes, L = 3λ/2.
    • Frequency of harmonics on a string: f = (1/2L) * √(T/μ), where T is tension and μ is mass per unit length.

    Stationary Waves in Air Columns

    • Closed end of an air column: node.
    • Open end of an air column: antinode.
    • First harmonic in an air column may differ from a string due to open/closed ends.

    Interference of Waves

    • Thomas Young's double-slit experiment demonstrated interference with coherent light.
    • Coherent light: all waves have a constant phase difference.
    • Double slit interference: bright fringes (Maxima) due to constructive interference; dark fringes (Minima) due to destructive interference.
    • Path difference: the difference in distance traveled by light from the two slits.
    • Young double-slit equation: W = λD/s, where W is fringe spacing, D is slit-screen distance, and s is slit separation.

    Diffraction of Waves

    • Diffraction occurs when waves pass through a narrow opening or around an obstacle.
    • Single slit diffraction: central maximum is twice the width of subsequent fringes.
    • Intensity of diffraction pattern falls away quicker than interference patterns.
    • Monochromatic light (e.g., a laser) produces clearly defined fringes.
    • White light splits into different colors due to different wavelengths diffracting at different angles.

    Diffraction Gratings

    • Diffraction grating: multiple narrow slits separated by a small distance (d).
    • Orders: bright fringes are produced at specific angles depending on wavelength and slit separation.
    • Zeroth order: central maximum.
    • Equation for diffraction grating: nλ = d sin θ, where n is the order, λ is the wavelength, d is the line spacing.

    Atomic Energy Levels

    • Electrons in atoms orbit the nucleus at specific energy levels (n = 1, 2, 3...).
    • Ground state: lowest energy level (n = 1).
    • Excited state: higher energy level.
    • Excitation: an electron can be excited by absorbing a photon or colliding with another electron.
    • De-excitation: an electron will fall back down to lower energy levels, emitting photons.
    • Energy of emitted photon: E = hf, where h is Planck's constant and f is the frequency.
    • Ionization: an electron is removed from the atom, leaving a positively charged ion.

    Emission and Absorption Spectra

    • Emission spectrum: shows the wavelengths of photons emitted by an object.
    • Absorption spectrum: shows the wavelengths of photons absorbed by a gas or plasma.
    • Spectra can be used to identify elements and determine the recessional speed of galaxies.

    Fluorescent Tubes

    • Fluorescent tubes use a cathode and anode to accelerate electrons through mercury gas.
    • Excited mercury atoms emit UV photons.
    • UV photons are absorbed by the fluorescent coating, causing it to emit visible light.

    Photoelectric Effect

    • Light can behave like particles (photons).
    • Photoelectric effect: electrons are emitted from the surface of a metal when light shines on it.
    • Kinetic energy (KE) of emitted electrons: KE = hf - Φ, where h is Planck's constant, f is the frequency, and Φ is the work function.
    • Work function: minimum energy required to liberate an electron from the surface of a metal.
    • Threshold frequency (f0): minimum frequency of light needed to liberate an electron.

    Wave-Particle Duality

    • Particles can also behave like waves.
    • Electron diffraction: electrons diffract when passed through a graphite target, producing an interference pattern.
    • De Broglie wavelength: λ = h/p, where h is Planck's constant and p is the momentum of the particle.

    Uncertainty in Measurements

    • All measurements have uncertainty.
    • Parallax error: error caused by viewing a measurement from an angle.
    • Zero error: systematic error that occurs if an instrument is not properly calibrated.
    • Resolution: the smallest difference that an instrument can measure.
    • Uncertainty: usually ±0.5 of the resolution.
    • Mean value: used to reduce random errors.
    • Error bars: used to represent uncertainty on graphs.
    • Line of best fit: used to represent the trend of data points.
    • Line of worst fit: used to determine the maximum and minimum possible gradients.

    Uncertainty and Resolution

    • The uncertainty of a measurement is equal to the resolution of the measuring tool when the tool is aligned with the edge of the object being measured.
    • When the measuring tool is fixed and the measurement is determined by finding the difference between two points, the uncertainty doubles the resolution. This is because two uncertainties are combined.
    • Absolute uncertainty is a standard uncertainty with a unit, just like the measurement.

    Percentage Uncertainty

    • When multiplying or dividing values with uncertainties, convert absolute uncertainties into percentage uncertainties.
    • Add all percentage uncertainties regardless of the operation (multiplication or division).
    • Uncertainties always increase, except when taking the square root of a value. In this case, halve the percentage uncertainty.

    Calculating Final Uncertainty

    • To convert the total percentage uncertainty back into an absolute uncertainty for the final calculated value, multiply the total percentage uncertainty (as a decimal) by the calculated value.

    Straight Line Graphs in Physics

    • Aim for straight line graphs in physics experiments to determine the gradient and relationship between variables.
    • Variables are not always directly proportional.
    • Use transformations to ensure a linear relationship on the graph. For example, if frequency is proportional to the square root of tension (f^2 is proportional to T), plot f^2 on the y-axis and T on the x-axis to get a straight line.

    Log Graphs

    • Powerful for finding relationships between variables when the relationship is unknown.
    • Kepler used log graphs to discover his third law of planetary motion.
    • Plotting log T against log R for planets in the solar system results in a straight line, revealing the relationship between the planet's orbital period (T) and distance from the Sun (R).
    • The gradient of the log graph reveals the relationship between the variables. In Kepler's case, the gradient is 1.5 (3/2), indicating that T^2 is proportional to R^3.
    • Log graphs always result in a straight line. The gradient determines the relationship.
    • The general straight line formula (y = mx + c) applies to log graphs. In Kepler's example, log T = 3 log R + log K.

    Interpreting Log Graphs

    • The gradient of a log graph provides the relationship between the variables.
    • Use log identities to manipulate the equation from the log graph.
    • In Kepler's example:
      • The gradient of 3/2 indicates the power of R (R^(3/2)).
      • The sum of two logs is equal to the log of the two things multiplied. Therefore, log(K * R^(3/2)) = log T.
    • Removing the log function on both sides, we arrive at the relationship: T is proportional to R^(3/2) or T^2 is proportional to R^3.

    Interpreting Graphs with Log Scales

    • A graph with a log scale is non-linear.
    • The scale is divided into powers of 10 (1, 10, 100, etc.), with smaller divisions within each power (1, 2, 3, …, 9, 10).
    • When reading values on a log scale, make judgments about values between lines.
    • Remember that 3 halfway to the next line is more like 3, not 5 (halfway 5).

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    Description

    This quiz covers key concepts related to forces, including vector representation, resultant forces, and the distinction between scalar and vector quantities. Additionally, it explores weight, work done, and gravitational potential energy with relevant calculations and applications. Test your understanding of these fundamental physics principles!

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