Physics Interview Questions & Answers

Physics Interview Questions

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Physics Interview Questions And Answers

Physics Interview Questions
    1. Question 1. What Is The Measure Of The Force Of Gravity On An Object?

      Answer :

      Force is the vector product of mass and acceleration: F = ma. Weight is a special case of that formula, where you substitute the acceleration of gravity, g, for a. We can therefore write: W = mg.1

      For example, if an object has a mass of 10 slugs2, its weight near the surface of the Earth is 10 x 32.2 (ft/s2) = 322 pounds (pound-force).

      If an object has a mass of 10 kilograms, its weight near the surface of the Earth is 10 x 9.8 (m/s2) = 98 newtons.

      You can measure the force of gravity on an object (i.e., its weight) by putting it on a scale.

    2. Question 2. What Is Neutral Buoyancy?

      Answer :

      Buoyancy is the net upward force experienced by an object submersed in a fluid. Pascal's principle dictates that fluid pressure on an object increases with depth, so there is greater pressure on the bottom of the object than the top, resulting in a net upward force. When an object's buoyancy is greater than its weight, the object will float.

      An object with neutral buoyancy has a density such that when it is fully submerged the upward force due to buoyancy is exactly equal to the downward force due to the weight of the object.

      In pure water this is a density of 1000 kg/m3 (1kg/litre)
      In seawater, this is a density of about 1025 kg/m3 (1.025kg/litre)

    3. Question 3. What Affect Does Electricity Have On Soil?

      Answer :

      Electrical current and ions can cause certain molecules (and moisture) to adhere to soil. Large amounts of current, such as a lightning strike, can fuse particles of soil into a crystalline structure, somewhat like glass.

    4. Question 4. What Is The Proper Formula Used To Calculate Acceleration?

      Answer :

      There are a few. The most famous is a = F/m, where F is the net force applied to a mass, m.

      Acceleration is also the change in velocity, Delta-V, divided by the change in time, Delta-t. So, a = Δv/Δt. For example, if an object's velocity changes from 10 meters per second to 20 meters per second in five seconds, its acceleration is (20-10)/5 = 2 meters per second per second, or 2 meters per second squared (m/s2).

    5. Question 5. How Much Does Automotive Oil Weigh?

      Answer :

      As a rough guide engine oil usually weighs about 0.87 kg/liter or about 7.2 pounds per US gallon.

      Unfortunately a rough answer is the best that can be done as there are hundreds of different types of engine oil with slightly different densities. To get an exact density we would have to know the details of the oil you're using. For a really accurate answer we would also have to state the temperature as the density of oil as with most fluids varies with temperature.

      Most oil manufacturers' provide data sheets for their products that should include density. If you search the manufacturer's web site you should be able to get an accurate figure for a particular grade.

    6. Question 6. What Is A Newton Meter?

      Answer :

      A unit of energy also known as a Joule. When a force of 1 Newton is applied on an object for a distance of 1 meter then 1 Joule of energy is used. It is the result of a vector calculation involving the meter (a unit of length in the SI system) and the Newton (the unit of force in the SI system).

      A unit of torque. (Turning force.) When a force of 1 Newton is applied at a distance of 1 meter from the pivot at right angle to the radius then a torque of 1 Newton Meter is present. It is the metric equivalent of lb ft. It is the name given to a device that measures force. It is a meter that measures Newtons.

    7. Question 7. What Instrument Is Used To Measure Volume?

      Answer :

      Liquid volume is measured with beakers, measuring cups, spoons, graduated cylinders, and the like. For regular objects, solid volume can be calculated. For irregular objects, their volumes can be determined by measuring the amount of liquid that is displaced by the object when it is submerged in the liquid. It is also used to measure the amount of pigs that fall from the sky!!!

    8. Question 8. How Does The Elevation And Air Pressure Affect The Boiling Point Of Water?

      Answer :

      The only factor that determines the boiling point of water at any altitude is the barometric pressure (the altitude itself doesn't actually matter, it's just that at higher elevation, the barometric pressure usually drops). However, water will boil at two different temperatures at the same elevation if you are in a high pressure weather system instead of a low pressure system.

    9. Question 9. What Is Time?

      Answer :

      This is the question that every true scientist dreads to be asked especially in a public setting by extremely inquisitive young students. We have learned to measure and calculate it relative to the natural arrangement of known and visible celestial bodies. This is the ultimate question you ask a theoretical astro physicist if you want to see them shake in their pants.

      To this day time can only be described by the measure of elapsed period using the SI unit, Seconds. It is the only SI unit that is freely allowed to shift depending on subject topic. For example in Astro physics, to measure distance between galaxies it would be impractical to use seconds as the measure of time it takes light to travel between the two galaxies.

      Time transcends everything known to man up to and including the universe, time has no beginning or end. Time is constant and infinite and we just tap in and out of it in reference to occurrence of an event.

    10. Question 10. What Are Wave Fronts?

      Answer :

      A wave front is an imaginary surface joining all points in space that are reached at the same instant by a wave propagating through a medium.

      Let's try some examples. When a rock is tossed into a calm lake, a surface disturbance radiates from the point where the rock broke the water. The leading edge of that entire wave forms a circle, and that circle is the wave front for that event. It is moving outward at a constant speed in all directions. Note that it's two-dimensional (2D). Want 3D? You got it.

      In a burst of chemical energy, a star shell explodes at a fireworks display. The light moves away from the origin in all directions at the same speed - the speed of light. And the 3D surface of this wave front is a sphere, and it is expands around the origin at the speed of light. Pick an arbitrary distance, say, 1 kilometer. Anyone at a distance of 1 km from the event in any direction will find that the wave front reaches him at the same instant of time as anyone else in any direction who is that 1 km from the event. Even someone in an airplane that is 1 km away will be on the wave front for an instant - that same instant as any other observers 1 km away. Note that the sound will arrive later - but it, too, radiates forming a spherical wave front. Our observers at 1 km distance from the event all experience the arrival of the sound wave at the same time.

    11. Question 11. How Many Pounds Does One Gallon Of Water Weigh?

      Answer :

      One wine measure or US gallon of water weighs 8.34 pounds. An Imperial Gallon is ten pounds of water at 62F and 30 inches of mercury air pressure.

      At 60F. The density of water (and any other liquid) is dependent on temperature. So a gallon of boiling water weighs less (8.00 pounds) than a gallon of water at 60F.

      So fill up your car first thing in the morning when it should be the coolest, you'll get more pounds of gasoline.

      Except that most vehicle fuels are stored underground and are at a pretty constant temperature. Fortunately it's pretty cool down there...

      Make it easy to remember; an ounce of water weights, about an ounce. can't be easier than that. So an American pint, 16 ounces, weighs about a pound. And an American gallon, 8 pints, about 8 pounds. Whereas an Imperial pint, 20 ounces; and an Imperial gallon, 160 ounces, about ten pounds. Just like it says, up top.

    12. Question 12. When A Radar Gun Says The Pitch Is 90 Miles Per Hour At What Point In The Balls Travel To Home Plate Is The Radar Gun Measuring The Velocity?

      Answer :

      The measurement is made at the point where the ball is when the trigger is squeezed and the contacts close to activate the unit. The gun responds in a "split second" by sending out a pulse, catching the return, and then comparing the two to discover the difference (the Doppler shift). It is so fast that the ball doesn't travel very far in the time it takes the unit to respond and resolve the speed.

    13. Question 13. Does Sunlight Reflected Off A Mirror Increase The Temperature Of The Sun-rays?

      Answer :

      A standard planar mirror will not increase the energy contained in the rays that reflect off it. In fact, there will be some loss of energy since the reflective surface is not perfect. There is some reduction in the light's intensity as it passes through the mirror's glass and reflects off the backing surface.

      Parabolic mirrors, on the other hand, focus and concentrate the light rays on a single point in front of the mirror, aptly named the focus. Although the energy is not amplified, it will be effectively increased because of the additive effect that will result when the light energy is concentrated.

    14. Question 14. How Is Radiation Emitted From The Body?

      Answer :

      The body radiates energy through thermal conduction through the skin to the air, clothes, etc, around the body. A small amount of energy would also be radiated as electromagnetic radiation with a peak wavelength directly related to the Kelvin temperature of the skin.

      Also very small amounts of other radiation are emitted due to naturally occurring radioactive isotopes in the body (i.e. Carbon-14).

    15. Question 15. What Are The Steps To The Scientific Notation?

      Answer :

      To write in scientific notation, you should first move the decimal point of the number to where the number is between 1 and 9. For example, change 567 to 5.67. Then count the number of places you moved the decimal. If you moved it left then the number is positive. If you moved it right then the number is negative. Finally times the number with the decimal point by 10 to the power of the number the decimal moved.
      Example: 500000 --> 5.00000 --> over 5 --> 5 x 105

    16. Question 16. Give One Advantage Of A Scanning Electron Microscope Over A Transmission Electron Microscope?

      Answer :

      The SEM has become more popular than the TEM as it can produce images of high resolution, greater clarity and three dimensional qualities and requires less sample preparation.

    17. Question 17. How Is Specific Gravity Defined?

      Answer :

      Specific Gravity, SG, is a unit less quantity that gives the scientist or engineers an idea of how dense a substance is compared to water. The density of water, which is one kilogram per liter (at 4 degrees C), is assigned a SG of 1.000. If a substance is denser than water, it will have a SG greater than 1.000; if it is less dense than water, its S.G. will be a value less than 1.000 (but greater than zero). Let's say a substance has a density of 2.5 kilograms per liter. That means that its SG is 2.5 (2.5 divided by 1.000).

    18. Question 18. What Is A Neutron?

      Answer :

      A neutron is a subatomic particle; it is one of the building blocks of the atom. It has a mass of about 1.675 x 10-27 kg. Its spin is + 1/2 and that makes it a fermions. Additionally, it has no electric charge, which is a distinctive feature. It is unstable when free in nature, and has a half life of about 886 seconds.

      The neutron could be said to be only "alive" to be part of an atomic nucleus as it ceases to exist after a while if left alone. When it wanders around loose, like after its release following decay event or a fission event, it may bump into another atomic nucleus and become captured by it. This process is called - no surprise - neutron capture. It is, after all, a nucleon, as is a proton, both of which make up an atomic nucleus. The neutron is made up of two down quarks and an up quark. When a neutron decays, it releases a proton (or, if you prefer, a hydrogen nucleus), an electron, and an antineutrino.

    19. Question 19. How Much Does Sea Salt Weigh Per Cubic Foot?

      Answer :

      Sodium chloride, NaCl, weighs 72 lb/ft3.

    20. Question 20. How Can Light Be Defined In Simplest Form?

      Answer :

      The common definition of 'light' (visible) is electromagnetic radiation visible to the human eye. It is only a small part of what is known as the 'electromagnetic spectrum' - which is the range of wavelengths of all possible electromagnetic radiation.

    21. Question 21. Does Weight Affect How Far You Jump?

      Answer :

      For the same leg strength / jumping technique, weight affects how far one can jump.
      Acceleration = Force / Mass

      With more mass, you cannot accelerate yourself as much when you jump with the same force. Imagine trying to jump with a small backpack full of sand strapped to your back. Your strength hasn't changed. That is, the amount of force you can deliver hasn't changed, but your mass has. You can't jump as high.


    22. Question 22. Is Air Travel Time The Same Whether Or Not The Plane Is Flying With Or Against The Rotation Of The Earth?

      Answer :

      All air travel takes the earth's rotation into account. Flights from east to west take less time in absolute terms, having nothing to do with time zones. The reverse is true with west to east flights, and even north-south flights must calculate the amount of rotational deviance while the aircraft is in flight. Long range naval cannons have been computing the earth's rotation under the projectile in aiming calculations for more than a century. Satellites in synchronous orbit that appear stationary are actually traveling at the earth's rate of rotation.

    23. Question 23. What Would Happen If A Disk One Light Second In Circumference Were To Spin At 60 Rpm?

      Answer :

      60 revolutions per minute is one revolution per second. 1 light second is the distance light travels in one second.

    24. Question 24. What Are Newton S Laws Of Motion?

      Answer :

      1. A body at rest will remain at rest and one in motion will remain in motion, until and unless acted upon by an external force. (Law of inertia).
      2. The rate of change of momentum of a body is proportional to the resultant force acting on the body in the same direction as its motion. (F = ma)
      3. For every action there is an equal an opposite reaction.

      Note: These laws apply only at speeds not approaching the speed of light and do not apply to sub-atomic particles.

    25. Question 25. Will A Dc Motor Actually Produce Voltage If It Is Spun In Reverse?

      Answer :

      It'll produce voltage if you spin it forwards, too. The only difference between a DC motor and a DC generator is what you use it for.
      A long time ago, cars had DC generators on them instead of AC alternators. When you replaced a generator, you had to "polarize" it so it would make electricity. You hooked it up to your battery and let it run, as a motor, for a few seconds. Don't try that with an alternator because you'll break it.

      If you're looking for a neat little elementary-school science project, you can use little Radio Shack electric motors as generators for things like windmills, water wheels, dynamos turned by bicycle tires..

    26. Question 26. What Is Density?

      Answer :

      Density is a physical characteristic, and is a measure of mass per unit of volume of a material or substance. It is a measurement of the amount of matter in a given volume of something.

      The higher an object's density, the higher it's mass per unit of volume. The average density of an object equals its total mass divided by its total volume. A denser object (such as iron) will have less volume than an equal mass of some less dense substance (such as water).

    27. Question 27. What Is An Alloy?

      Answer :

      An alloy is a homogeneous hybrid of two or more elements, at least one of which is a metal, and where the resulting material has metallic properties. The resulting metallic substance often have unexpected characteristics.

      Classification of Alloys :Alloys can be classified by the number of their constituents. An alloy with two components is called a binary alloy; one with three is a ternary alloy, and so forth. Alloys can be further classified as either substitution alloys or interstitial alloys, depending on their method of formation. In substitution alloys, the atoms of the components are approximately the same size and the various atoms are simply substituted for one another in the crystal structure. An example of a (binary) substitution alloy is brass, made up of copper and zinc. Interstitial alloys occur when the atoms of one component are substantially smaller than the other and the smaller atoms fit into the spaces (interstices) between the larger atoms.
      An alloy is a metal mixed with another metal to make it stronger.

    28. Question 28. What Is The Law Of Machines?

      Answer :

      Machines which are used to lift a load are governed by the "Law of machines", which states that the effort to be applied on the machine (p) is related to the weight (w) which it can lift as -
      p = mw + c
      Where m and c are positive constants which are characteristics of the machine.

    29. Question 29. What Is Pascal S Principle?

      Answer :

      Pascal's Principle states that the pressure is transmitted evenly through a liquid. That's why when you inflate a balloon with air it expands evenly in all directions.

    30. Question 30. How Does The Arrangement Of Atoms In Most Solids Differ From The Arrangement Of Atoms In A Liquid?

      Answer :

      The arrangement of atoms in solids are different from those in liquids in that they are unable to move from their location in the solid, where they can move in the liquid. A solid's atoms are vibrating very rapidly, but the molecules are all locked into place, whereas in a liquid the molecules are free to move around. Also in general the atoms of a solid are closer together than those of a liquid with the exception of water, whose solid form is less dense.

    31. Question 31. When An Object Moves With Constant Velocity Does Its Average Velocity During Any Time Interval Differ From Its Instantaneous Velocity At Any Instant?

      Answer :

      No. Its velocity, average velocity and instantaneous velocity will all be the same at any (or every) time an investigator makes an observation.

    32. Question 32. What Is Cardiac Output?

      Answer :

      Cardiac output is the volume of blood the heart pumps within one minute. Cardiac output (CO) is equal to the stroke volume (SV) of the heart multiplied by the heart rate (HR). Thus, cardiac output is given by the equation: CO=HR X SV.

    33. Question 33. What Is The Longest Lasting Synthetic Periodic Element?

      Answer :

      A good candidate would be curium 247 (247Cm), which has a half-life of 1.56 × 107 years. That's 15,600,000 years (15.6 million years).

    34. Question 34. What Happens When You Travel Across The Dateline?

      Answer :

      If westbound, the day changes to the next day. If eastbound, the day is the day before. Seems strange, but it all works out.
      Let's imagine we're on the beach in the early evening west of the dateline at 4:59 PM Tuesday. If we swim eastward across the dateline and continue east seven time zones, it will be 11:59 PM Monday. We rest from all this exercise and ponder the strangeness of turning back a day. Whew! One more minute and it will be Tuesday anyway. Continue 17 more time zones (24 totals) eastward and it will be 4:59 PM Tuesday. Just like we left it. It works just fine in the reverse going the other way.

    35. Question 35. What Are The Applications Of Nmr Spectroscopy?

      Answer :

      The main applications of NMR stereoscopy are the elucidation of the carbon-hydrogen backbone of organic compounds and the determination of the relative stereochemistry of the same molecule.

    36. Question 36. What Are The Weights In Pounds Of Liquid Gallons?

      Answer :

      First, you must know the specific gravity of the liquid then you can calculate the weight by multiplying the specific gravity by 8.34 lbs. 8.34 lbs is the weight of a gallon of water that has a specific gravity of 1.

    37. Question 37. How Do You Calculate Tensile Strength?

      Answer :

      Tensile strength isn't really calculated; it's measured. It is defined as the point at which a sample of material fails when subjected to tensile stress. The unit of measure of tensile strength (and stress) is the Newton per square meter (N/m2), also known as the Pascal (Pa). Tensile strengths of various building materials, such as steel, are measure in millions of Pa.

    38. Question 38. Why Is It Important Not To Expose A Patient To X-rays For Too Long?

      Answer :

      Someone who is exposed to x-rays too long can develop cancer, skin burns, anemia, or other serious conditions.

    39. Question 39. Why Does The Pilot Tilt The Outer Wing Of The Airplane Inward While Taking A Turn?

      Answer :

      Airplanes have two control surfaces involved when turning, the ailerons are on the trailing edge of the wings. By moving them in opposite directions, one up one down, the plane tilts, the lift the wings are generating now causes the plane to turn instead of going up. The rudder which is vertical at the back turns the plane to the left and right, but the rudder alone can turn the plane but not change its direction (side slipping) so in order to turn correctly you must use both the rudder and the ailerons.

    40. Question 40. What Is Ntu In Thermodynamics?

      Answer :

      ntu is nothing but number of transfer units it is one of the method used to find the heat transfer of hot and cold body it is applicable to both parallel and counter flow.

    41. Question 41. Why Have The Electron And The Proton The Same Charge Whereas The Proton Is 1836 Times Heavier?

      Answer :

      Because the electric charge depends on the mass times the radius of a particle and whereas the mass of the proton is 1836 heavier than the mass of the electron, the radius of the proton is 1836 times smaller. Thus, the product of mass time's radius is in both particles the same and therefore they have the same charge.

    42. Question 42. How Do You Convert From Pascal To Torr?

      Answer :

      Converting Pascal to torr

      The pascal is a smaller unit of pressure than the torr. There are 133.32 Pascal per torr. Hence, divide your pressure measurement in pascal by 133.32 to convert to torr.

      If your measurement is in torr to begin with, multiply it by 133.32 to convert to pascal.

    43. Question 43. Which Atomic Model Did Erwin Schrodinger Create?

      Answer :

      Schrödinger's wave equation was based on the Heisenberg uncertainty principal that the position and velocity of a electron cannot be determined accurately (accuracy in one will sacrifice accuracy in another). Schrödinger's wave equation gave a wave function, which squared gave the probability cloud of electrons. Therefore, Schrödinger's contribution resulted in the electron cloud model of the atom.

    44. Question 44. Is A Sewing Needle Magnetic Or Non Magnetic?

      Answer :

      When you buy it in the store it is not magnetized, but if you rub it with a magnet it becomes magnetic.

    45. Question 45. What Is Meant By 4th Dimension?

      Answer :

      When a reference is used to four-dimensional co-ordinates, it is likely that what is referred to, is the three spatial dimensions plus a time-line.

    46. Question 46. What Are The Three Particles That Make Up An Atom?

      Answer :

      Atoms are made up of protons, neutrons, and electrons. The protons and neutrons are found together in the core of the atom, called the nucleus, which is in the center. The electrons are found moving around the nucleus (at different energy levels) in what is called the electron cloud.

      Note that in hydrogen most all of it is made up of just a lone proton and an electron. There are no neutrons in the most common isotope of hydrogen (1H).

      Protons and neutrons, which are called nucleons when they're found in an atomic nucleus, are further made of still smaller subatomic particles called quarks.

    47. Question 47. Advantage Of Fixed Pulley?

      Answer :

      Fixed pulleys are used to change the direction of a force.

    48. Question 48. What Is The Difference Between Isolation Transformers And Step Up Or Step Down Transformer?

      Answer :

      Actually an isolation transformer may be physically the same as a Step up/Step Down transformer. The main difference is in the way  they are used.

      Another difference is that in a normal transformer there will be capacitance between the 2 windings, between the windings and core, between the core and shell, etc.

      These capacitances bring in high frequency noise from outside, which will be transmitted in the secondary circuit. So [in an isolation transformer] wires are connected between each component, (not direct contact, but with insulation present). This permits a leakage current and eliminates unnecessary capacitance.

    49. Question 49. How Do You Calculate Shaft Power?

      Answer :

      Shaft power P = (2(pi) * (angular Speed in rpm) * (Torque at shaft))/ 60
      Torque of a solid shaft is given by (pi/16)* (Shear stress of material of shaft) * (Dia of shaft3)

    50. Question 50. What Is Free Fall Acceleration?

      Answer :

      On earth free fall acceleration is 9.81 meters per second per second or 32.2 feet per second per second, not including air resistance.

      Around these parts, free fall acceleration is the acceleration due to earth gravity on a body that is not acted on by an outside force (like air resistance or a bungee tether).

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