Experiment M1: Instrumental Errors
(Not in books)
Q1: What is the Least Count of a Screw Gauge? Ans: The least count of the screw gauge is defined as the distance moved by the screw when the cap rotates through one division on the circular scale. It is calculated by dividing the pitch of the screw by the total number of divisions on the circular scale.
Q2: What is the Pitch of the Screw Gauge? Ans: The pitch is the distance between two consecutive screw threads, measured parallel to the axis, or the distance the screw moves forward or backward during one complete rotation of the cap. The pitch of a screw gauge is usually 0.5 mm or 1 millimeter.
Q3: Explain the two types of Instrumental Error for the Slide Calipers. Ans: There are two types of zero errors:
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Positive Zero Error: The zero of the Vernier scale is in advance of the zero line of the main scale by an amount x mm.
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Negative Zero Error: The zero of the Vernier scale is behind that of the main scale by an amount x mm.
Experiments 2 & 3: Weight and Sensitivity of a Balance
(The Q&A below covers general principles of mass, weight, and balance sensitivity, related to Experiments 2 and 3)
Q1: What is the difference between mass and weight? Ans: Mass is the quantity of matter contained in it. The weight of a body is the pull of the earth by the gravitational force and varies from place to place. Mass is constant everywhere, because it does not depend on the earth’s attraction.
Q2: What do you measure with a balance? Ans: Mass is measured by comparing its weight with that of standard ‘weights’ from a weight box.
Q3: What are the requisites of a good balance? Ans: A good balance must be true, sensitive, stable, and rigid.
Q4: What is the condition that a balance may be true? Ans: (i) The pans must be of equal weight and (ii) The arms of the beam must be of equal lengths.
Q5: Why are the beam and the pans of a balance supported by knife-edges by a gate plate? Ans: In order to diminish the friction of working parts of support and suspension.
Q6: When will the beam of the balance be horizontal? Ans: When the moment of the weight of the body to be weighted and that of the standard weight about the fulcrum are equal.
Q7: Is the weight of a body constant at various places on the surface of the earth? Ans: No, it varies from place to place. It decreases when the body is taken (i) at high altitude (ii) in deep mine (iii) from pole to equator. At the center of the earth it vanishes.
Q8: When you close the shutter of the balance? Ans: Close the shutter and turn the levers, the pointer oscillate equally on both sides of the control mark.
Q9: How does sensitivity very with load? Ans: See Figure 2.
Q10: What is sensitivity of a balance? Ans: See the text.
Q11: What are the advantages of the method of oscillation? Ans: In a very sensitive balance the pointer goes on oscillating about the mean position for a long time and the resting point can be readily calculated by the method of oscillation.
Q12: What are the conditions for sensitiveness of balance? Ans: (i) The arms of the beam must be long. (ii) The distance of the center of gravity of the beam from the central knife-edge must be small.
Q13: What are the conditions for a balance said to be stable? Ans: (i) The arms of beam must be small. (ii) The distance of the center of gravity of the beam from the central knife-edge must be large and (iii) The beam must be heavy.
Q14: Why are the weights put on the right hand pan and the body on the left-hand pan? Ans: The weights are to be varied and for convenience of putting them, they are placed on the right hand pan.
Experiment 4: Young’s Modulus and Rigidity Modulus
Q1: Define stress, strain and Young’s modulus of elasticity. Ans:
- Stress: The restoring force per unit area acting on the body. Stress = F/A.
- Strain: The ratio of change in dimension to its original dimension. It is a pure ratio and has no limit.
- Young’s Modulus: The ratio of normal stress to longitudinal strain within its elastic limit. Mathematically, .
Q2: What do you mean by elastic limit and breaking stress? Ans:
- Elastic limit: The maximum stress up to which a body exhibits the property of elasticity.
- Breaking stress: The breaking weight per unit area of cross-section.
Q3: Which is more elastic rubber or steel? Ans: Steel is more elastic than Rubber.
Q4: Define modulus of rigidity? What is the unit of rigidity? Ans: The ratio of the tangential stress to the shearing strain is called rigidity of modulus ().
Q5: What is the effect of temperature on rigidity? Ans: The property of solid is to resist the forces tending to change its shape with increasing temperature. Rigidity modulus changes with changing temperature.
Q6: What is moment of inertia? Ans: The sum of the product of the mass and the square of the distance of different particles of the body from the axis of rotation is called moment of inertia.
Q7: How do the pendulum oscillations and torsional oscillations differ? Ans: Pendulum oscillations are controlled by gravity, while torsional oscillations are controlled by the amount of torsion in the suspending wire.
Q8: What is the advantage of this method? Ans: is evaluated by counting time and not deflection. Another advantage is that it requires a very short specimen, and is also determined simultaneously.
Q9: Define tangential stress, tangential strain, shearing stress and shearing strain and compare Y and . Ans: See the text book, you will find it from theory.
Q10: What are the two types of oscillations occur in this experiment? Ans: i) Pendulum oscillations/ simple harmonic oscillations and ii) Torsional oscillations.
Q11: Define Hooke’s law of elasticity. Draw the stress-strain diagram and explain the behavior of material under stress. Ans: See the text book, you will find it from theory.
Experiment 5: Surface Tension of Water by Capillary Tube Method
Q1: Define surface tension. What is its units and dimension? Ans: If a straight line of unit length is drawn in the liquid surface, the portion of the surface on opposite sides tends to draw away from each other with a force that acts tangential to the surface and perpendicular to the line drawn. Its unit in the C.G. S system is dyne/cm. The dimension of surface tension is .
Q2: What is the angle of contact? Ans: The angle between the two tangent planes with the liquid.
Q3: Define cohesive forces? Ans: Cohesive force is the force of attraction between two similar kinds of molecules, and adhesive force is that between two dissimilar kinds of molecules.
Q4: What is the effect of temperature on surface tension? Ans: Surface tension decreases with an increase in temperature because the density of water decreases, causing the surface tension to also decrease.
Q5: What is critical temperature? Ans: Critical temperature is the highest temperature at which a gas can be liquefied by pressure alone.
Q6: What surface tension does vanish? Ans: Surface tension vanishes at the critical temperature.
Q7: What is the effect of electrification on surface tension? Ans: Surface tension decreases when a liquid is electrified.
Q8: On what factors does the surface tension of a liquid depend? Ans: i) On the nature of the liquid. ii) On the nature of surface in contact. iii) On the temperature of liquid; higher the temperatures, less the surface tension.
Q9: Should the top of the capillary tube be open or closed? Ans: The top of capillary tube must be open.
Q10: Why don’t you use distilled water instead of tap water? Ans: During the distillation process, water vapor comes in contact with various tube joints having wax sealing and is thereby contaminated.
Q11: Why water rises and mercury drops in the tube? Ans: See the text book.
Q12: What happened when a drop of water and mercury falls on the wooden surface? Why? Ans: See the text book.