Physics

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  • PHYSICS
    • is a branch of science which deals with the study of matter, energy, force and motion and the way they relate to each other. is an “experimental science” wherein we observe the phenomena and nature and try to find patterns and principles that relate these phenomena
  • MEASUREMENT
    • is the process of determining the amount, quantity, degree or capacity by comparison with an accepted standard.
  • PRECISION
    • is a measure of the consistency or repeatability of measurements.
  • ACCURACY
    • is the degree of exactness of a measurement compared to the expected value, or the most probable value of the variable being measured.
  • THE TWO SYSTEM OF MEASUREMENTS
    • ENGLISH SYSTEM
    • also called the BRITISH SYSTEM.
    • used only in the United States and some African countries.
    • the system of unit used is the FPS or the “foot pound-second”.
  • 2. METRIC SYSTEM
    • established in 1791 by the French Academy of Sciences. in 1960, it has been known officially as the “International System” or SI (the abbreviation for its French name, Système Internationalè).
    • is used by most of the rest of the industrialized countries.
    • two system of units are known: the MKS (meter kilogram-second) and the CGS (centimeter-gram second
  • THE SEVEN FUNDAMENTAL SI UNITS OF MEASUREMENTS
    • METER (m)
    • the unit of length.
    • in 1960, a meter is measured using the wavelength of the orange-red light emitted by atoms of krypton in a glow discharge tube.
    • but in November 1983, the length standard was changed again: a meter is the distance that light travels in a vacuum in 1/299792458 second
  • 2. KILOGRAM (kg)
    • the unit of mass.
    • is defined to be the mass of a particular cylindrical slab of platinum-iridium alloy.
    • this cylinder is kept at constant temperature and humidity in a dustless vault in Sevres near Paris, France
  • 3. SECOND (s)
    • the unit of time.
    • from 1967 up to present, a second is based on an atomic clock, which uses the energy difference between the two lowest energy states of the cesium-133 atom.
    • when bombarded by microwaves of precisely the proper frequency, cesium atoms undergo a transition from one of these states to the other.
    • a second is defined as the time required for 9192631770 cycles of this radiation.
  • 4. KELVIN (K)
    • the unit of temperature.
    • named after William Thomson, commonly known as Lord Kelvin, the 1st baron of Kelvin. 
    • the standard is based on the point at which solid, liquid and gaseous water coexist simultaneously (the “triple point” which has an assigned value of 273.16 K
  • AMPERE (A)
    • the unit of electric current.
    • named in honor of the French scientist Andrè Marie Ampere (1775-1836).
    • the standard is based on the mutual force experienced by parallel current-carrying wires
  • CANDELA (cd)
    • the unit of luminous intensity.
    • the standard is based on the amount of radiation emitted by a certain object, known as a blackbody radiator, at 2046 K (the freezing point of platinum)
  • MOLE (mol)
    • the unit for number of particles.
    • the standard is based on the number of atoms contained in a 0.012 kilogram of carbon-12 isotope
    1. What is the SI unit for pressure?
    b. Pascal
  • 3. Which of the following is equivalent to the unit “candela”?
    d. lumen/steradian
  • 4. What refers to the mass which is accelerated at the rate of one foot per second per second when acted on by a force of one pound?
    A.1 slug
  • 5. The size of some bacteria and living cells is in the order of
    d. micrometer
  • 1 ton is equivalent to: (ECE Board Exam, October 2019)
    d. 946.25 kg
  • 1 kJ is equivalent to (ECE Board Exam, October 2019)
    b. 0.948 Btu
  • 35 lb.ft is equivalent to (ECE Board Exam, October 2019)
    c. 47.45 N.m
  • WORK
    • is defined as the product of the force and displacement in the direction of the force.
  • ENERGY – is the capability to do work.
    a. POTENTIAL ENERGY – is the energy possessed by an object by virtue of its position or configuration.
    PE = wh = mgh
    b. KINETIC ENERGY – is the energy possessed by an object by virtue of its motion.
    KE = 1/2 mv^2
  • POWER – is the time rate of doing work.
    P = W/t = Fd/t = Fv
    1W = 1J/s
    1hp = 746 W = 550 ft-lb/sec
  • Who coined the term energy in 1807?
    b. Thomas Young
  • . What is the energy something possesses by virtue of its mass?
    c. rest energy
  • POTENTIAL ENERGY – is the energy possessed by an object by virtue of its position or configuration.
    KINETIC ENERGY – is the energy possessed by an object by virtue of its motion. MECHANICAL ENERGY - the sum of potential energy and kinetic energy present in the components of a mechanical system
  • 8. An object is being pulled along the ground by a 75 N force directed 28o above the horizontal. How much work does the force do in pulling the object to a distance of 8 meters?
    W = Fd cosθ
    d. 530 J
  • 9. A ball at the end of a 180 cm long string swings as a pendulum. The ball’s speed is 4 m/s as it passes through its lowest point. To what height above the lowest point will it rise before stopping?
    PE = KE
    mgh = 1/2 mv^2
    c. 0.816 m
  • A 0.25 hp motor is used to lift a load at the rate of 5 cm/s. How great a load can it lift at this constant speed?
    P=W/t = Fd/t = Fv
    a. 381 kg
  • What is the kinetic energy of a baseball with mass of 0.15kg moving with a speed of 36m/s? (ECE Board Exam, October 2019)
    a. 97J
  • This refers to the work needed to accelerate a body of a given mass from rest to its stated velocity. (ECE Board Exam, October 2019)
    a. Kinetic energy
  • WAVE
    • is a vibratory disturbance that moves through a medium.
    • they are produced in all forms of matter even in empty space where ordinary matter does not exist.
  • TYPES OF WAVES
    1. TRANSVERSE WAVE
    • a wave in which the vibration direction is perpendicular to the direction of the wave propagation.
    • examples are water waves, waves in strings under tension, electromagnetic waves (light and radio waves).
    • in a transverse wave, the maximum upward displacement is known as CREST and the maximum downward displacement is known as TROUGH
  • 2. LONGITUDINAL WAVE
    • a wave in which the vibration direction is parallel to the direction of propagation.
    • examples are sound waves, waves in rods and in vibrating helical spring.
    • in a longitudinal wave, the area of maximum compression is called CONDENSATION while the area of maximum separation is called RAREFACTION
  • WAVE EQUATIONS:
    1. WAVE VELOCITY – the distance through which each wave moves per second.
    v = wavelength / t = wavelength f
    1. Velocity of a Transverse Waves on a stretched string: v = sqrt(FI/m) = sqrt(F/plinear)
    2. . Velocity of Longitudinal Waves in solids and liquids: v= sqrt(E/p)
    3. Velocity of Longitudinal Waves in gases: v=sqrt(kRT/MW)
  • 2. FUNDAMENTAL FREQUENCY OF A STRETCHED STRING
    f1 = v/2l = 1/2l sqrt(Fl/m)
    For the nth harmonic:
    fn = n x f1
  • 3. LAWS OF VIBRATING STRING
    • Law of Lengths
    • a.the frequency of a vibrating string is inversely proportional to its length.
    • f1l1 = f2l2
    • b. Law of Diameters  the frequency of a vibrating string is inversely proportional to its diameter.
    • f1d1 = f2d2
  • c. Law of Tensions
    • the frequency of a vibrating string is directly proportional to the square root of the tension.
    • f1/f2 = sqrt(T1/T2)
    d. Law of Densities
    • the frequency of a vibrating string is inversely proportional to the square root of its density.
    • f1/f2 = sqrt(p2/p1)
  • 11. When waves go from one place to another, they transport
    d. energy only
  • 12. A wave that needs a material medium through which it can travel as it transfers energy is called
    b. mechanical wave