Ohm's Law Viva Questions and Answers

Ohm's Law Experiment Viva Questions and Answers

(i) State Ohm's law

Ans: At constant temperature the ratio of the potential difference between the end of a conductor to the current through it is constant. V/I = constant

(ii) Distinguish between emf and potential difference

Ans: emf is the potential difference between the terminals of a cell when no current is drawn from it. It is equal to the amount of work done by the source in moving unit charge once around a complete circuit.

Potential differences between two points on a conductor are the work done in moving unit charge from one point to other.

(iii) What is meant by specific resistance or resistivity?

Ans: ρ = RA/ l. It is equal to the resistance of a wire of length one metre and cross sectional area 1 m²

(iv) What is the unit of resistivity?

Ans: Ohm-meter. Ωm

(v) Why are connecting wires thick and covered with cotton thread?

Ans: Thick copper wire has negligible resistance. They are covered with cotton to avoid short circuiting.

(vi) What is the material of wire used for making a rheostat?

Ans: Manganin or constantan

(vii) What is the effect of temperature on resistance?

Ans: Resistance of a wire increases with temperature

(viii) How will you convert a galvanometer into (a) ammeter (b) voltmeter?

Ans:

(a) By connecting a low resistance in parallel.

(b) By connecting a high resistance in series

(ix) Is Ohm's law a universal law?

Ans: No. It is not a universal law. It fails on semi conductor and for resistances at very low temperature

(x) What is super conductivity?

Ans: In some substances the resistance completely disappears below a critical temperature. This phenomenon is called super conductivity

(xi) What happens if voltmeter is connected in series in a circuit?

Ans: A voltmeter is an tool for finding the potential difference between two points. Hence the voltmeter is connected between the two points. More over the voltmeter has a very high resistance. Hence the current in the circuit is very much reduced.

(xii) Aim of the Ohm's Law Experiment?

Ans: To study current—voltage relationship (i.e. to verify Ohm's Law) using an ammeter and a voltmeter; and, hence to find the resistivity of the given resistor.

(xiii) Apparatus of the Ohm's Law Experiment?

Ans: Lead accumulator, a resistance wire (resistor), ammeter, voltmeter, rheostat, key etc.

(xiv) Theory of the Ohm's Law Experiment?

Ans: If V is the potential difference applied to a conductor of resistance R and I is the current flowing through the conductor, according to Ohm's law,

V/I = R, a constant

If r is the radius and l is the length of the conductor, the resistivity of the conductor,

ρ = R x (π r²)/l

(xv) Procedure of the Ohm's Law Experiment?

Ans: The accumulator, resistance wire R, ammeter, rheostat and key are connected in series. The voltmeter is connected in parallel to R.

The circuit is closed and the rheostat is adjusted to make voltmeter to show a definite reading V. The reading I of the ammeter is noted. V/I is calculated.

Adjusting the rheostat suitably, a number of sets of values are noted for V and I. In each case V/I is calculated. It is found to be a constant verifying Ohm's law.

A graph is drawn with V along the Y-axis and I along the X-axis. The graph is a straight line. This also verifies Ohm's law.

The mean value of V/I is calculated. This gives the resistance R of the resistor. R is also calculated from the graph by finding its slope. The average value of R is found out. The radius r of the resistor is determined using a screw gauge. Its length l is also measured. The resistivity ρ of the resistor is calculated from the equation,
ρ = R x π r²/l

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Jolly's Bulb Apparatus Experiment

The Jolly's Bulb Apparatus Experiment Viva Questions

(i) State the unit of pressure in S.I.

Ans: Nm^-2

(ii) What is one atmosphere?

Ans: It is the pressure exerted by a column of 76 cm of mercury at 0 °C.

P = hdg = 0.76 x 13.6 x 10³ x 9.8 = 1.013 x 10⁵ Nm^-2

(iii) Why should the air enclosed in the bulb be dry?

Ans: The presence of water vapour alters the reading

(iv) State Charles law

Ans: The volume of a given mass of gas varies directly as its temperature in Kelvin scale when pressure is kept constant. The pressure of a given mass of gas varies directly as its temperature when volume is kept constant ie, V ∝ T and P ∝ T

(v) Why do you use a capillary tube to connect the bulb to the reservoir?

Ans: To ensure that most of the air enclosed is at the constant temperature of the bath

(vi) What is the boiling point of pure water at normal pressure in Kelvin scale?

Ans: 273 K

(vii) How do you define pressure coefficient of a gas?

Ans: It is defined as the ratio of the increase in pressure of the gas at constant volume per degree rise of temperature to its pressure at 0 °C

(viii) Is the pressure coefficient the same for all gases? If so what is its value?

Ans: Its value is same for all gases and is equal to 1/273

(ix) Aim of the Jolly's Bulb Apparatus Experiment?

Ans: To study the relation between pressure and temperature of a sample of air at constant volume

(x) Apparatus of the Jolly's Bulb Apparatus Experiment?

Ans: Jolly's bulb apparatus, water bath, thermometer, etc. The Jolly's bulb apparatus consists of a spherical glass bulb A connected to a narrow capillary tube bent twice at right angles. There is a fixed mark M made on this tube as shown in the figure. The free end of the tube is connected to a reservoir R of mercury by means of thick rubber tubing. The reservoir can be raised or lowered and can be fixed in any position. The readings of the mercury levels may be noted on a scale S.

(xi) Theory of the Jolly's Bulb Apparatus Experiment?

Ans: For a given mass of gas (air) at constant volume, the pressure P is directly proportional to its absolute temperature T.

i.e., P ∝ T or (P/ T) = a constant

Boyles Law Viva Questions

Boyles Law Viva Questions and Answers

(i) What is the S.I. unit of pressure?

Ans: N.m^-2

(ii) Atmospheric pressure at sea level is 0.76 m of mercury. What is the pressure in N.m^-2? Density of mercury = 13.6 x 10⁵ kg/m³.

Ans: P = hdg = 0.76 x 13.6 x 10⁵ x 9.8 = 1.013 x 10⁵Nm^-2 or one Atmosphere.

(iii) State Boyles law

Ans: At constant temperature, the volume of a given mass of gas varies inversely as its pressure ie, v ∝ 1/p or, pv = constant

(iv) What is gas constant? It is a universal constant for all gases at S.T.P.

Ans: R =PV/T = 1.01 x 10⁵ x 22.4 x 10^-3/273 = 8.3 J/mol/k.

(v) What are the limitations of Boyles law?

Ans: It does not hold good for high pressures and low temperatures. It is also not true for saturated vapour.

(vi) What is critical temperature?

Ans: It is the temperature above which a gas cannot be liquefied by applying pressure.

(vii) Do all gases obey Boyles law

Ans: Real gases do not obey Boyles law. So called permanent gases like O₂, H₂, etc obey Bolyle's law at ordinary temperature and pressure.

(viii) What is an ideal gas?

Ans: A gas which obeys Boyles law and Charles law is called perfect gas or ideal gas. Intermolecular force is zero

(ix) Why do we use mercury for measuring pressure

Ans: It and does not wet glass. Hence a small column of liquid is enough

(x) What is the shape of P.V. diagram?

Ans: It is a part of a hyperbola.

(xi) Aim of Boyles Law Experiment?

Ans: To study the variation of volume of a sample of air with its pressure at constant temperature using Boyle's law apparatus.

(xii) Apparatus of Boyles Law Experiment?

Ans: Boyle's law apparatus Boyle's law apparatus consists of a uniform glass tube AB closed at one end. It is fixed vertically on a stand with its open end downwards. The tube is connected to a reservoir R by means of a rubber tube. The reservoir contains mercury. The glass tube AB contains pure dry air. The reservoir can be raised or lowered and can be fixed at any position. Thus the pressure and volume of air inside the glass tube can be varied. A scale is fixed between AB and the reservoir.

(xiii) Theory of Boyles Law Experiment?

Ans: According to Boyle's law, at constant temperature, volume V of a given mass of gas (air) is inversely proportional to its pressure P.

i.e., P ∝ 1/V

Therefore, PV = a constant.

Since the glass tube is uniform, V ∝ l, the length of the air column in the glass tube.

P ∝ (1/l); ie, Pl = a constant

Inclined Plane Viva Questions with Answers

Inclined Plane Viva Questions with Answers

(i) What do you understand by an inclined plane?

Ans: It is a smooth plane hinged to the base, so that it can be set at any desired angle.

(ii) Why do you oil the pulley and the axle of the roller?

Ans: To eliminate friction

(iii) The roller of weight W is in equilibrium on a smooth inclined plane of angle θ, and the effort ‘P' is required to keep the roller in equilibrium. How are they related

Ans: P = W sinθ

(iv) What is the shape of the graph and between P and sin θ?

Ans: The graph is a straight line.

(v) What is the significance of the slope of the graph?

Ans: The slope of the graph gives the weight of the roller

(vi) What is the mechanical advantage of the inclined plane?

Ans: It is the ratio of the weight of the roller to the effort. M.A = W/p

(vii) Theory of Inclined Plane Experiment?

If P is the force (effort) applied parallel to an inclined plane upwards on a roller of mass m just to keep roller in equilibrium, then,

P = mg sin θ; where mg sin 0 is the component of the gravitational force (ie., the component of the weight W of the roller) acting downwards along the inclined plane. P ∝ sin θ; where sin θ =h/l;l is the length and h the height of the plane.

(viii) Procedure of Inclined Plane Experiment?

The weight w of the scale pan is found out by a common balance The plane is adjusted to a convenient angle θ. The roller is placed on the plane and the pulley adjusted to make the string parallel to plane. Weight w₁ is placed in the pan to make the roller just move up the plane with a uniform speed. Next, keeping the roller near the top edge of the plane, the weight w₂ required in the scale pan to make the roller just to move down with uniform speed is found out. The mean effort,

P= [(w₁ + w₂)/2] + w

The downward force along the inclined plane acting on the roller on account of the gravitational force, i.e., mg sin θ, is equal to the effort P.

P = mg sin θ;

where m = W, is the mass of the roller.

To find sin θ, the length l and the height h of the plane are measured. Then, sin θ is calculated from the equation.

sin θ = (h/l)

The experiment is repeated for different angles of the plane. A graph is drawn with P along the Y-axis and sin θ along the X-axis. The graph is found to be straight line. This shows that P which is equal to the component of the weight of the roller along the plane is directly proportional to the sine of the angle of the inclined plane. The slope of the graph gives the weight of the roller.

The angle θ of the plane is noted from the value of sin θ (Use scientific calculator or logarithm table). A graph is drawn with P and θ. The graph is a curve bent downward. This gives the relation between the components of the weight of the roller along the plane at the angle of the plane.

For more Viva Questions on Inclined Plane

Resonance Column Viva Questions

Resonance Column Viva Questions and Answers

(i) What are stationary waves?

Ans: When two waves of the same frequency and amplitudes travel in opposite directions along a straight line at the same speed, their super position gives rise to stationary waves

(ii) What are nodes and antinodes?

Ans: Node is a position of zero displacement and antinode is a position of maximum displacement

(iii) In a stationary wave what is the distance between successive nodes?

Ans: λ/2, where λ is the wave length.

(iv) What is end correction or edge effect?

Ans: The antinode at the open end of a tube is formed slightly out side the open end. The distance from the open end to the antinode is called end correction e = 0.3d where d is the diameter of the pipe

(v) What is meant by resonance?

Ans: When two notes of the same frequency are sounded together the intensity of sound is maximum and they are said to be in resonance or in unison

(vi) The experiment is called resonance column experiment why?

Ans: When we excite a tuning fork and hold it at the mouth of the tube at resonance the frequency of the air column and the frequency of the turning fork are equal. We obtain the frequency of the air column by resonance method

(vii) What is the effect of temperature on the velocity of sound in air?

Ans: The velocity of sound in air is directly proportional to the square root of temperature in Kelvin scale v ∝ √T.

(viii) In a resonance column experiment what is the functions of water in the jar?

Ans: It only acts as an agent for closing the tube to make the tube a closed tube of easily variable length

(ix) What is meant by supersonic speed?

Ans. The speed greater than that of sound in air ie, 331 m/s at 0°C

(x) If we take kerosene oil in place of water in the resonance column experiment will the resonance position change?

Ans: Remains unchanged

(xi) Why is second resonance feebler than the first?

Ans: At second resonance the vibration in the air column corresponds to the first overtone which is very week

(xii) What type a waves you get in resonance column?

Ans: Longitudinal

(xiii) Is it necessary to have a tube of circular cross section?

Ans: Not necessary.

(xiv) Aim of Resonance Column experiment?

Ans: (a) To determine the velocity of sound in air at room temperature by the resonance column and hence to determine the velocity of sound in air at 0°C.

(b) To find the end correction.

(xv) Apparatus for the Resonance Column experiment?

Ans: Resonance column apparatus, tuning forks, rubber hammer etc. Resonance column apparatus includes a long metal tube erected vertically in a tall jar containing water. The tube can be set in any desired position. The length of the air column in the tube can be varied by stretching or lessening the tube.

Sonometer Viva Questions and Answers

Sonometer Practical Viva Questions and Answers

Sonometer Experimental Set Up

(i) Does sound travel in vaccum?

Ans: No, A material medium is needed for its propagation

(ii) What are the frequency limits of audibility?

Ans: 20 Hz and 20,000 Hz

(iii) What type of waves are light waves and sound waves?

Ans: (a) Transverse (b) Longitudinal

(iv) On what factors does the frequency of a tuning fork depend?

Ans: It depends on the nature of the material and length of the prong

(v) What type of waves are produced in a sonometer wire?

Arts: In the tuned position stationary waves are produced. Otherwise there are transverse waves

(vi) Why is the wooden box of the sonometer hollow?

Arts: Air in the box vibrates in resonance and increases the intensity of sound.

(vii) What are the functions of the bridges?

Ans: They reflect the sound and produce stationary waves

(viii) Can a rubber cord be used in place of the wire?

Ans: The rubber cord is not rigid and so its vibration die down quickly.

(ix) What are beats?

Ans: When two notes of nearly equal frequencies are sounded together there is waxing and waning of sound ie, ups and downs in intensity. This phenomenon is called beats

(x) What happen when the paper rider in the sonometer experiment flies off'?

Ans: It happens when the frequency of the wire between the bridges and the tuning fork are exactly equal

(xi) What happen to the frequency of the turning fork when one of the prongs is loaded with wax?

Ans: The frequency of the fork decreases

(xii) What are the factors on which frequency of the segment of a string depends?

Ans: n ∝ 1/l ; n ∝ 1/√T and n ∝ 1/√m

(xiii). What is a sonometer? 

Sonometer is an instrument used to measure the frequency of a vibrating body producing sound. 

(xiv). What type of waves are produced in a sonometer wire? 

In a sonometer wire stationary waves are produced which are transverse in nature. 

(xv). What is the function of knife edges placed below the wire of the sonometer? 

The transverse waves produced in the wire get reflected from the knife edges resulting in stationary waves. 

(xvi). What is the function of 'rider' in sonometer experiment? 

The rider will fly off only when the vibrations produced in the wire of very large amplitude. This happens only when the frequency of vibration of the wire becomes equal to that of tuning fork at resonance. 

(xvii). What is meant by transverse wave? 

If the particles of the medium vibrate perpendicular to the propagation of the wave motion, it is called transverse wave. 

(xviii). What is meant by progressive wave? 

A wave that propagates in an extended medium without attenuation is called progressive wave. 

(xix). What is meant by stationary wave? 

When two waves of same type propagate along a straight line, but in opposite directions, their superposition upon each other gives a resultant wave which does not travel either way with time is called stationary wave. 

(xx). Define wavelength. 

Wavelength of a wave is the distance travelled by the wave during a periodic time. 

(xxi). Why is the wooden box of sonometer hollow? 

A hollow wooden box may enclose air which vibrates in resonance and increases the intensity of sound. 

(xxii). Define node. 

In a stationary wave, point where zero amplitude is called node. 

(xxiii). Define antinode. 

In a stationary wave, the points where maximum amplitude is called antinodes. 

(xxiv). What is the distance between two consecutive nodes or antinodes? 

λ/2 (half the wavelength λ) 

(xxv). Define beats. 

The phenomenon of regular variation in the intensity of sound with time at a particular position, when two sound waves of nearly equal frequencies, superimpose on each other is called beats. 

(xxvi). What is a fundamental note? 

It is a note of the lowest frequency. 

(xxvii). What are overtones? 

Overtones are notes whose frequencies are simple multiples of the fundamental notes. 

(xxviii). What is meant by unison? 

Two notes of same frequency are said to be in unison. 

(xxix). Define pitch. 

Pitch is a characteristic of musical sound, which distinguishes a sharp sound from a dull sound. 

(xxx). How does the loading or filling at the prongs of a tuning fork affect its frequency? 

The frequency of the tuning fork decreases by loading and increases by filling at the prongs.

(xxxi) Aim of Sonometer experiment?

To find the relation between frequency and length, for a constant tension, frequency and diameter of a stretched string.

(xxxii) Apparatus for the Sonometer experiment?

Sonometer, slotted weights, tuning forks of known frequencies, rubber hammer, paper rider, steel wire, etc. The sonometer consists of a long hollow wooden box with a peg at one end and a vertical pulley at the other end. One end of the experimental wire is attached to the peg and the other passes over the pulley. To keep the wire under tension, a suitable weight is suspended at the free end of the string by a weight hanger. Two movable bridges A and B are provided for the purpose of altering the vibrating length of the wire.

(xxxiii) Theory of Sonometer experiment?

The frequency n of transverse vibration of a string stretched under a constant tension T is inversely proportional to the length l of the string.

i.e., n ∝ (1/l);

Therefore, n x l = a constant

(xxxiv) Procedure of Sonometer experiment?

The bridges A and B are placed at a small distance apart. A light paper rider is placed on the string between the bridges. A tuning fork of frequency n is excited and its stem is pressed on the sonometer box between the bridges. The length of the string is altered by adjusting the distance between the bridges till the rider vibrates vigorously. This happens when the segment AB of the string vibrates in unison with the tuning fork. The length l of the vibrating segment is measured and n x l is calculated.

The experiment is repeated with the other tuning forks without changing the tension. In all cases it is found that nl is a constant.

A graph is plotted with n along the X-axis and (1/l) along the Y-axis. The graph is found to be straight line. This also shows that n ∝ (1/l).

Surface Tension and Viscosity Viva Questions

Surface Tension and Viscosity Experiment

The surface tension (capillary rise) Viva Questions and Answers

(i) Define surface tension

Ans: It is defined as the force acting tangential to the liquid surface and perpendicular to unit length of an imaginary line drawn on the surface of the liquid

(ii) What is the unit and dimension of S.T?

Ans: Unit-Nm^-1; Dimension MLT^-1

(iii) How is surface tension related to surface energy?

Ans: They are the same.

(iv) What is the difference between adhesive and cohesive forces?

Ans: Attraction between molecules of the same kind-cohesive. Attraction between molecules of different kind-adhesive.

(v) What is angle of contact?

Ans: The angle between the tangent to the liquid surface at the point of contact and the solid inside the liquid.

(vi) What is meant by capillarity?

Ans: Rise of liquid in capillary tube is called capillarity

(vii) For mercury there is capillary depression. Why?

Ans: Angle of contact is oblige (140 °)

(viii) What are the factors on which capillary ascent depends?

Ans: Inversely proportion to the radius, inversely proportional to density and directly proportional to surface tension.

(ix) If the angle of contact were 90°. What is capillary accent?

Ans: Zero

(x) Is surface tension is a molecular phenomenon or atomic

Ans: Molecular phenomena.

(xi). What is a capillary?

Ans: A tube with fine bore.

(xii). What is the unit of surface tension?

Ans: N/m

(xiii). Give the value of surface tension of water?

Ans: It is 72.7 x 10^-3 N/m at 20° C

(xiv). Define capillary rise.

Ans: Rising of a liquid in a capillary tube is called capillary rise.

(xv). Why doesn't mercury rise in the capillary tube?

Ans: For mercury and clean glass, the angle of contact is obuse. Hence mercury does net rise in the capillary tube.

(xvi). Why does water rise in the capillary tube?

Ans: For water and clean glass, the angle of contact is acute. Hence water rises in the capillary tube.

(xvii). How does surface tension vary with temperature?

Ans: Surface tension decreases with increase in temperature.

(xvii) Aim of surface tension experiment?

Ans: To find the surface tension of water by capillary rise.

(xix) Apparatus for the Surface tension experiment?

Ans: A narrow capillary tube of uniform bore of known radius, beaker containing water, travelling microscope and so on.

The Viscosity Viva Questions and Answers

(i) Define the coefficient of viscosity.

Ans: It is the tangential force necessary to keep a unit velocity gradient amid two layers each of unit area. 

(ii). Define fluid.

Ans: Fluid is a substance which begins to flow when external force is applied on it.

(iii). Give example for fluids?

Ans: Liquids and gases.

(iv). Define viscosity.

Ans: Viscosity is a fluid property in which an internal frictional force acts while the fluid is in motion and resist the relative motion. 

(v) What is Stoke's formula?

Ans: F=6πrηv , Where r = radius, η = fluid velocity, v = sphere velocity

(vi) What is meant by Reynold's number?

Ans: Rn=(ρVL)/μ , Where ρ = density, V = flow speed, L = linear dimension, μ = dynamic velocity

(vii) Give the Newton's equation for viscous force.

Ans: F= -ηA(dvx/dz)

(viii) Define the unit 'poise'

Ans: It is the unit of viscosity in C.G.S system. The unit is in honor of Poiseuille who did important works on viscosity

1 poise = dynes. second/cm²

(ix) What is meant by terminal velocity?

Ans: Terminal Velocity is defined as the maximum constant velocity attained by a body when falling freely in a viscous medium.

(x). What happens to viscosity of a liquid when temperature increases?

Ans: Viscosity decreases

(xi). What happens to viscosity of a liquid when pressure increases?

Ans: Viscosity increases (except water) 

(xii) What is the effect of temperature on viscosity of liquids?

Ans: Viscosity decrease with the increase in temperature.

(xiii) What is the effect of temperature on the viscosity of gases?

Ans: The viscosity of gasses increase with rise in temperature.

(xiv) Aim of the viscosity experiment?

Ans: To determine the coefficient of viscosity of a given liquid by measuring the terminal velocity of a given spherical body.

(xv) Apparatus for the viscosity experiment in lab?

Ans: A tall glass jar of about 1 m long and 2 cm radius, viscous liquid (ex: castor oil or diesel), lead shots or small ball bearings of different size, screw gauge, stop watch etc.

Simple Pendulum Viva Questions and Answers

Simple Pendulum Viva Questions and Answers

(i) Who invented simple pendulum?

Ans: Galileo

(ii) Is `g' a vector quantity?

Ans: yes

(iii) What is the effective length of a simple pendulum?

Ans: It is the total length from the point of suspension to the centre of gravity of the bob

(iv) Why do we use heavy bob which is small in size?

Ans: A heavy bob has enough restoring force to overcome the air resistances. A small bob has less resistance due to air. So heavy bob, small in sizes is used as bob

(v) What is a seconds pendulum?

Ans: It is a simple pendulum whose time period is 2 seconds. It takes one second to move from one extreme position to the other end.

(vi) If the given bob is replaced by a wooden bob of the same size will the time period change?

Ans: It remains the same

(vii) What will happen to the time period if a simple pendulum is setup on the surface of the moon?

Ans: The time period will increase as the value of 'g' on the surface of the moon in less than that on the surface of the earth.

(viii) While oscillating, the amplitude of the pendulum must be small-why?

Ans: For small amplitude sin θ = θ in radians. Then the simple pendulum has simple harmonic oscillations.

(ix) What is the relation between 'g' and 'G'? Gin

Ans: g = Gm/R²

(x) What is the value of 'g' at the centre of the earth?

Ans: zero.

(xi) If you set up a simple pendulum in an artificial satellite orbiting the earth what will be the period of the pendulum?

Ans: Inside the satellite g = 0. Hence period is infinite.

(xii) What is meant by periodic motion?

Ans: A motion which repeats after equal intervals of time is called periodic motion.

(xiii) What is meant by amplitude?

Ans: It is the maximum displacement of a particle from its mean position.

(xiv) What happens if the bob of the simple pendulum has rotatory motion along with the translatory motion?

Ans: The rotatory motion will produce twist in the thread which changes the time period.

(xv) Define time period of an oscillating body.

Ans: It is the time taken by the oscillating body to complete one oscillation.

(xvi) Define frequency.

Ans: Number of periodic motions that occurs in unit time is called frequency of the periodic motion.

(xvii) How is frequency related to period of oscillation?

Ans: Period = 1/frequency

(xviii) How will the value of 'g' be affected if the earth stops rotating?

Ans: The value of 'g' would increase in general. The variation is maximum at the equator and minimum at the poles.

(xix) Apparatus of the Simple Pendulum

Ans: A simple pendulum, stop clock, metre scale, vernier calipers, stands etc. The simple pendulum consists of a metallic bob suspended by a light inextensible string passing through the split halves of a cork.

(xx) Theory of Simple Pendulum

Ans:The period of a simple pendulum of length l at a place where the acceleration due to gravity is g, which is given by,

T = 2π √(l/g);

Therefore, g = 4 π² (l/T²)

(xxi) Aim of the Simple Pendulum Experiment

Ans: (a) To determine the acceleration due to gravity at the place.

(b) To draw l – T² graph and hence to find the length and period of the Pendulum.

(xxii) Procedure of the Simple Pendulum Experiment

(a) To find the acceleration due to gravity at the place

The period of oscillation, T = (t/30), is calculated. The experiment is repeated with different lengths l (60, 70, 80 ………….. cm) of the pendulum. In each case l/T² is calculated. In all cases it is found that (l/T²) is a constant. The average value of (l/T²) is determined and the acceleration due to gravity (g) is calculated. g = 4π²(l/T²)

(b) To draw T² — I graph

The experiment is performed as explained above. A graph is drawn with l along the X-axis and T² along the Y-axis. This graph is a straight line.

(i) To find the length of the seconds pendulum

A seconds pendulum is one for which the period of oscillation is 2 seconds. From the graph the length 1 corresponding to T² = 4 is determined. This gives the length of the seconds pendulum.

(ii) To find the length of the pendulum whose period is 1.5 seconds, the length l corresponding to T² = 1.5² = 2.25 is determined from the graph.

(iii) From the graph, 1/T² = AB/BC. Therefore, g = 4π²(AB/BC)

The Concurrent Forces Viva Questions and Answers

The Concurrent Forces Viva Questions and Answers

(i) State parallelogram law of forces

Ans: If two forces acting at a point be represented in magnitude and direction by the adjacent sides of a parallelogram drawn from a point, the resultant force is represented in magnitude and direction by the diagonal of the parallelogram drawn from the same point

(ii) State triangle of forces

Ans: If three forces acting at a point can be represented in magnitude and direction by the sides of a triangle taken in order then the forces is in equilibrium,

(iii) What is meant by resultant of a set of force?

Ans: It is that single force which effectively replaces the set of forces

(iv) What are concurrent forces?

Ans: Forces acting at a point are known as concurrent forces.

(v) What is Lami's theorem?

Ans: If three forces acting at a point keep it in equilibrium, then each force is proportional to the since of the angle between the other two.

(vi)

What is the angle between them

Ans: 45°

vii) Will the forces 15N, 20N and 40N acting at a point keep it in equilibrium?

Ans: No

viii) What are the main sources of error in the experiment?

Ans: (a) Friction at the pulleys. (b) Thread cannot be weight less.

(ix) If there is a lot of friction at the pulleys in what way the result of this experiment be affected?

Ans: The forces represented by the hanging weight will have values lower than what are given by the relation W = mg

(x) Apparatus of Concurrent Forces

Ans: Parallelogram law apparatus consisting of two frictionless pulleys attached to a framework fixed on the top of a vertical drawing board, light inextensible strings, weights and weight hangers and the given body.

(xi) Theory of Concurrent Forces

Ans: If three co-planer concurrent forces P, Q and R keep a point in equilibrium, the resultant of P and Q will be equal and opposite to R, the equilibrant.

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Physics Experiment's Viva Questions

Some Physics Experiment's Viva Questions

1. The Moment Bar Viva Questions and Answers

Moment Bar

(i) What is the principle of the moment bar?

Ans: The principle of moment. That is, the algebraic sum of the moment of the forces acting on a rigid body is zero.

(ii) Why do you suspend the metre scale at the centre of gravity to find the weight of a body?

Ans: In order to make the moment of the weight of the scale about the point of suspension zero.

(iii) Can you find the relative density of a body using moment bar.

Ans: Yes

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2. The Helical Spring Viva Questions and Answers

3. The Friction Viva Questions

4. The Young's Modulus Viva Questions

5. The Newton's Law of Cooling Viva Questions

6. The Vernier Calipers

7. The Screw Gauge

8. The Spherometer

9. The Common Balance

10. The Concurrent Forces

11. The Simple Pendulum

12. The Surface Tension

13. The Viscosity

14. The Sonometer

15. The Resonance Column

16. The Inclined Plane

17. The Boyles Law

18. The Jolly's Bulb Apparatus

19. The Ohm's Law

20. The Meter Bridge

21. The Post Office Box

22. The Potentiometer

23. The Figure of Merit of Galvanometer

24. The Conversion of Galvanometer into Ammeter

25. The Conversion of Galvanometer into Voltmeter

26. Frequency of AC Mains using Sonometer

27. The Concave Mirror

28. The Convex Lens

29. The Convex Mirror

30. The Concave Lens

31. The Refraction through a Prism

32. The Refractive Index of a Glass Slab Using Travelling Microscope

33. The PN Junction Diode

34. The Zener Diode

35. The Mapping of Magnetic Field

36. The Tangent Galvanometer

37. The Spectrometer

38. The Logic Gates 1 (AND and OR gates)

39. The Logic Gates 2 (NOT gate)

40. The Logic Gates 3 (Using switches)

Spherometer and Common Balance Viva Questions

Spherometer and Common Balance Viva Questions and Answers

The Spherometer

(i) What is the principle of a spherometer?

Ans: It works on the principle of a micrometer screw.

(ii) Why is the spectrometer called so?

Ans: Since it is used to measure the radius of curvature of a spherical surface, it is known as spectrometer.

(iii) How will you calculate the least count of a spherometer?

Ans: LC = Pitch/No. of head scale divisions.

(iv) Is there any zero correction for a spectrometer? 

Ans: No

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The common balance

(i) What is the principle of a physical balance?

Ans: It is form of lever of first order and works on the principle of moments.

(ii) What are the requisites of a good balance?

Ans: Truth, sensibility and stability

(iii) What is a true balance'?

Ans: A balance is true if the beam remains horizontal when the pans are empty or when they are equally loaded

(iv) What is meant by sensibility of a balance?

Ans: It is the mass required to change the resting point by one division

(v) What is the function of the plumb line in a balance?

Ans: We can level the balance with the help of the plumb line so that the beam rotates in a vertical plane

(vi) While weighing, the shutter must be closed. Why?

Ans: This is to avoid disturbance due to air current

(vii) Is it advisable to weigh a hot body?

Ans: No, with hot body convection currents are set up in air, which disturb the equilibrium.

(viii) What is the difference between mass and weight?

Ans: According to Newton's first law of motion mass is a measure of the inertia pos-sessed by the body which makes it resist any change in its state of rest or motion. It is also defined as the quantity of matter contained in it. Weight of a body is the force with which the earth attracts the body towards its centre

(ix) What are the S.I. unit of mass and weight?

Ans: Mass—kilogram; Weight—Newton

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Screw Gauge Viva Questions and Answers

Screw Gauge Viva Questions and Answers

(i) Name the instrument used for measuring the thickness of a piece of paper

Ans: Screw gauge.

(ii) What is meant by pitch of a screw gauge?

Ans: It is the distance advanced by the screw for one complete rotation of the head.

(iii) The pitch of a screw is 1 mm and the number of divisions on the head scale is 100. What is the least count?

Ans: Least count =  pitch/ No: of divisions on the head scale = 1/100 = 0.01 mm

(iv) What is zero error of a screw gauge?

Ans: If the zero of the head scale does not coincide with the zero of the pitch scale when the end of the movable screw is in contact with the stud, the screw gauge is said to have zero error.

(v) If the zero of the head scale is 5 divisions above the line of graduation of the pitch scale when the gap is closed, what is the zero error? What is the zero correction? Least count of the vernier = 0.01 mm

Ans: zero error = -5 x 0.01 = -0.05 mm and zero correction = +0.05 mm

(vi) If the zero of the head scale is 5 divisions below the line of graduation of the pitch scale when the gap is closed, what is the zero error and correction? Least count = 0.01 mm

Ans: zero error = +5 x 0.01 = +0.05 mm and zero correction = -0.05 mm

(vii) Why do we take a number of observations for the diameter of a wire?

Ans: Even if the wire appears uniform it may not be true. So to take the average value we take a set of readings

(viii) Why do you stop rotating the screw as soon as the ratchet begins to turn between the fingers?

Ans: When the ratchet begins to turn, the two faces are in contact or in contact with the body held between them. The device avoids undue pressure on the screw.

(ix) Aim of Screw Gauge Experiment

 

Ans: To find

(a) the diameter of a wire and

(b) thickness of an irregular glass plate using screw gauge and find their volumes.

 

(x) Theory of Screw Gauge Experiment

 

Ans: Dimension measured = P.S.R + fraction = P.S.R + (H.S.R x L.C);

where  P. S . R = Pitch Scale Reading,

H.S.R = Head Scale Reading

and L.C = Least count of the screw gauge

Volume of the wire =  πr²l; where r = radius of the wire and l = length of the wire

 

(xi) How to find the pitch of the screw?

 

Ans: Pitch = Distance moved/Number of rotations

 

(xii) How to find the least count of the screw gauge?

 

Ans: The least count of the screw is the distance moved by it when it is rotated through one division of the head scale.

Least count = Pitch/No: of divisions on the head scale.

 

(xiii) How to find the zero correction?

 

Ans: The screw is turned till the tip touches the stud. If the zero division does not coincide with zero of the pitch scale, then it is zero error. So a correction has to be applied. If it is not screwed, there is no zero correction. If it is over screwed, the zero correction is positive (+3 divisions). If it is under screwed, the zero correction is negative (-2 divisions).

 

(xiv) How to find the diameter and volume of the wire?

 

Ans: Diameter of the wire = P.S.R + fraction = P.S.R+ (corrected H.S.R. x L.C)

Volume (V) of the wire is calculated using the equation, V =  πr²l

 

(xv) How to find the thickness and volume of the glass plate?

 

Ans: The given glass plate is griped between the tip of the screw and the stud. The P.S.R and the H.S.R are noted as before. The thickness of the glass plate is

t = P.S.R + (corrected H.S.R) x LC

The glass plate is placed over a graph paper and its outline is traced on the graph paper. The area A of the glass plate is taken from the graph paper. The volume of the glass plate is calculated from the equation.

V = A x t

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Vernier Caliper Viva Questions and Answers

Vernier Caliper Viva Questions and Answers

(i) What is meant by least count of an instrument?

Ans: It is the smallest measurement that can be made with the given instrument

(ii) What is meant by least count of a vernier calipers?

Ans: It is the smallest length that can be measured with the instrument and it is equal to the difference between a main scale division and a vernier scale division.

(iii) The least count of a vernier is 0.001 cm. What is the order upto which it can measure length accurately?

Ans: It can measure accurately up to 10-3 cm.

(iv) What part of the vernier calipers is the vernier scale?

Ans: The sliding scale along the main scale is called vernier scale.

(v) Which is the instrument you will use to measure the internal and external diameter of a tube?

Ans: Vernier calipers

(vi) Apparatus of Vernier Calipers

Ans: The vernier calipers, the given cylinder and the metallic rectangular block. The vernier calipers consists of a main scale and a small subscale called vernier scale. The main scale is usually graduated in mm. The vernier scale is a sub-scale which can slide along the main scale and can be fixed at any position with the help of a screw. Usually there will be 10 divisions on the vernier scale which are equivalent to 9 mm on the main scale. The main scale and the vernier scale are provided with jaws at their ends. When the jaws are in contact, the zero of the vernier coincides with the zero of the main scale.

(vii) Theory of Vernier Calipers

Ans: When a body is gripped between the jaws, the main scale reading (M.S.R) is the reading on the main scale just before the zero mark of the vernier scale and the vernier scale reading (V.S.R) is the number of the vernier division which coincides with some division of the main scale.

If L. C is the least count of the vernier calipers,

Dimension measured = M.S.R + fraction = M.S.R + (V.S.R x L.C)

Volume of a cylinder = πr²l;

where r is the radius and l is the length of the cylinder.

Volume of the rectangular block = lbh;

where l, b and h are length, breadth and height of the block.

If r is the internal radius and h is the depth of the calorimeter,

Internal volume of the calorimeter = πr²h

(viii) Procedure of Vernier Calipers

To find the least count (LC) of the vernier calipers

The least count is the difference between a main scale division and a vernier scale division. if (n — 1) main scale divisions are divided into n vernier scale divisions then,

Least count = 1/n x 1 m.s.d

(a) To measure the dimensions of the cylinder

To find the length of the cylinder, it is gripped lengthwise between the jaws. The main scale reading (M.S.R) immediately before the zero of the vernier, and the division of the vernier (V.S.R) coinciding with any of the main scale division are noted.

The length of the cylinder, l = M.S.R. + a fraction = M.S.R. + (V.S.R x L.C)

The experiment is repeated by keeping the vernier calipers at different positions of the cylinder and the average length is calculated.

Similarly the mean diameter of the cylinder is determined. The radius (r) of the cylinder is calculated from its diameter.

Volume of the cylinder = πr²l

(b) To find the volume of the given rectangular block of known mass by measuring its dimensions with the vernier calipers and hence to find its density.

The length (I), breadth (b) and the height (h) of the rectangular block is determined as in the case of the measurement of the length of the cylinder.

Volume of the rectangular block, V = l x b x h

If m is the mass of the block, its density, d = m/V

(c) To find the internal radius (r), depth (h) and volume (V) of the calorimeter.

The upper ends of the jaws are put inside the calorimeter and open them till each of them touches the inner wall of the calorimeter. The main scale reading (M.S.R) and the vernier scale reading (V.S.R) are noted. The inner diameter of the calorimeter = M.S.R + (V.S.R x L.C). The experiment is repeated keeping the projections of the jaws tightly inside the calorimeter at different positions and the average diameter is calculated. The inner radius r of the calorimeter is calculated from its diameter.

The end of the main scale strip is kept on the upper edge of the calorimeter. The vernier scale is pushed over the main scale till the tip of the pointer attached to the back of the vernier touches the bottom of the calorimeter. The M.S.R and V.S.R are noted. The depth h of the calorimeter = M.S.R + (V.S.R x L.C). The experiment is repeated and the average depth is calculated. 

The volume V of the calorimeter is calculated from the equation,

V = πr²h

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