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Physics Practicals Class XI

Determining the mass of two different objects using beam balance

Objective of the Experiment :

To determine the mass of two different objects using a beam balance.

Theory Of The Experiment
Viva-Voce On Physical Balance Experiment (Q&A)

Theory

Objective

To find the mass of the given body by sensibility method, using a beam balance. 

Theory

The beam balance is a device used for the determination of the mass of a body under gravitation.  

It consists of a beam supported at the centre by an agate knife edge resting on a support moving inside a vertical pillar. The beam carries a light pointer which moves over a scale. There are two stirrups at the ends of the beam which carries two scale pans of equal masses along with adjusting nuts. These can be adjusted to make the pointer  oscillate within the scale when the balance is raised. The balance is mounted on a platform provided with three leveling screws which make the pillar vertical. There is a plumb line which shows whether the pillar is vertical or not. The balance is enclosed in a glass case in order to avoid disturbances due to air.

Correct mass of the body using the beam balance, 

------------------------(1)

Where,
W   - Mass in the pan
R0 - Zero resting point
R   - Resting point with the body counter-poised with weight W 
S   - Sensibility of the balance. 
The sensibility S, the weight required to shift the resting point by one division is calculated from the equation,
      

R1 – Resting point with 10 mg in the right pan

 

Learning outcomes

  • Students able to know the working principle of beam balance.
  • Students learn about the sensibility of beam balance.

Materials required:

  •     Beam balance
  •     Box of weights
  •     A rectangular wooden block
  •     Pendulum bob

Procedure:

How does a beam balance work?

The leveling screws at the base are adjusted to make the pillar vertical. The beam is gently raised by turning the handle. If the pointer does not oscillate almost equally on either side of the central division of the scale, adjust the nuts suitably at the ends of the beam. 

Before determining the mass of the body one needs to calibrate the beam balance.

1.    To find the zero resting point (R0)

The balance is released and the pointer is allowed to oscillate freely. Three or five successive readings (three to the left and two to the right on the scale against which the pointer turns back during oscillations) are taken. These readings are called the turning points. The average turning point on the left and the average turning point on the right are separately calculated. The mean of these averages gives the zero resting point ( R0).

The method of calculation is given below.

Turning Points (T.P)
Left Right

X1

X2

X3

Y1

Y2
Mean T.P  
​ ​
Resting Point ,​

 

2.    To find the sensibility of the balance (S)

For finding the sensibility, 10 mg weight is placed in the right pan and the resting point (R1) is determined as before. Then the sensibility S is calculated using the equation (2) explained in the 'Theory' tab .

 Now let’s find out the mass of the body (M)   

The balance is arrested by turning the handle. The given body is placed in the left pan and it is counterbalanced by a known mass (W) in the right pan. The resting point (R) is determined. The correct mass of the body can be calculated using the relation (1) explained in the the 'Theory' tab.

Note: The pointer of the beam balance always rests near the pan having less weight.

Procedure :

For Sensibility Checking

  • Release the knob.
  • Note three consecutive turning points (three at left and two at right).
  • Arrest the knob.
  • Click on open door.
  • Place 10 mg in the right pan of the balance.
  • Click on close door button.
  • Now release the knob.
  • Note three consecutive turning points(three  at left and two at right ).

After sensibility calculation,

  • Click on the open door button.
  • Click on 10 mg to remove it from the balance.
  • Select an object by a single click on bob/wooden block.
  • The object would counter balanced by selecting weights given on a single click.
  • Click on close door button.
  • Release the knob to note the turning points as before.
  • Repeat the steps for adding more weights or reduce weights to counter poise the weight in the left pan.
  • Click on the show result button to view the result.
  • A reset button is also provided to reset the entire the simulation.

Note: The pointer of the Beam balance always rest near the pan having lesser weight.

Observations:

To find the weight of the body 

Loads in Pan Turning Points Mean Turning Points Resting Point
Left Right Left Right Left Right  
Nil Nil         R0=
Nil 10 mg         R1=

GIven 

Body

 W=----g         R=

 

Calculations

1.    Sensibility,   =................................................g / div
2.    Correct mass of the body,    = ............................g 
                                                =………………kg

Result

The mass of the body = ………...............……kg

 

Viva-Voce [Physical Balance]

Question. 1. What do you understand from mass of a body ?

Answer. It is the quantity of matter possessed by the body.

 

Question. 2. What are units  of mass ?

Answer. S.I. unit of mass is kilogram and C.G.S. unit of mass is gram. 1 kg = 103  g.

 

Question. 3. What is one kilogram ?

 Answer. It is the mass of a platinum-iridium cylinder, having diameter equal  to height, stored in a special vault in the International Bureau  of Weight and Measures at Severe,  near  Paris  in France

 

Question. 4. Dene weight.

Answer Weight of a body is dened as the force with which the body is attracted by the earth towards its centre. W = mg.

 

Question. 5. What is difference between mass and weight ?

Weight W = mg varies  from place  to place, because g varies.

 

Question. 6. Dene inertial  mass of a body.

Answer. The mass which offers inertia, is called  inertial mass.

Question. 13. Dene inertia.

 

Answer. It is the property of a body, due to which the body continues in its state of rest  or of uniform  motion

 

 

 

Question. 7. How can  we measure inertial  mass ?

 

Answer. Inertial mass can be measured by using  relation m1  = F/a. Hence,  for measuring inertial mass, a known force  F is applied  on the body and acceleration (a) produced is measured.

 

 

Question. 8. Dene gravitational mass of a body.

 

Answer. The mass which offers gravitational attraction, is called  gravitational mass.

 

 

 

Question. 9. How can  we measure gravitational mass ?

 

Answer. Gravitational mass can be measured by using  relation mG= W/g.

Hence,  for measuring gravitational mass, weight  W of a body is measured at a place  of known value of g.

 

 

 

Question. 10. What is relation between inertial  mass and  gravitational mass of a body ? Answer. The two masses are found  to be equal.

 

 

Question. 11. Describe a phenomena in which both  the inertial  and  the gravitational masses of a body take  part.

Answer. In simple harmonic motion of the bob of simple pendulum, both the inertial and the graviational masses of the bob play their part.

Gravitational mass mG provides the restoring force.  Inertial mass ml controls the acceleration of the bob.

 

 

Question. 12. Which instrument determines the inertial  mass ? Answer. An inertial balance determines the inertial mass.

 

 

Question. 15. Which instrument determines the gravitational mass ?

 

Answer. A spring  balance and a physical (beam) balance determine the gravitational mass.

 

 

 

Question. 16. Does  the spring balance measure mass or the weight ? Answer. The spring  balance measures weight.

 

 

Question. 17. What is the principle of working  of a spring balance ?

 

Answer. It works  on Hook’s law. It works  on the fact  that  when  a body is suspended from a vertical  spring, the body produces extension in the length  of the spring  proportional to its weight.

 

 

Question. 18. What is principle of working  of a physical balance ? Answer. It works  on the principle of moments.

 

 

Question. 19. What is principle of moments ?

 

Answer. It tells that  bodies of equal  weight  suspended at equal  distances from the fulcrum on the two sides of the beam, keep the beam horizontal.

 

 

Question. 20. What is a true balance ?

 

Answer. A balance which has  arms of equal  length  and pans of equal  weight, is called  a true balance. Its beam is horizontal with empty pans and also  when  equal  weights are put on the pans.

 

 

Question. 21. What is a sensitive balance ?

 

Answer. When a small  difference in weights of two bodies in the two pans of the balance, makes the beam pointer to turn through sucient angle, the balance is said  to be sensitive.

 

 

Question.22. Dene resting point  of a balance.

 

Answer. Resting point (R.R) of a balance is the point (position) on the scale at which the pointer will come to rest  when  the beam stops oscillating.

 

 Question. 23. What is atomic unit of mass ?

 

Answer. Atomic unit of mass is atomic mass unit (a.m.u.).  It is 1/12th of mass of an atom of the carbon isotope 12C. Its value is 1.66 x 10-27 kg.

 

Question. 24. What is astronomical unit of mass ?

Answer The density of a substance is dened as its mass per unit volume.

 

Question. 27. What is unit of density ?

Answer. In C.G.S. system, unit of density is gram per cm3 (g-cm-3). In S.I., unit of density is kilogram per metre3 (kg-m-3).

 

 

Question. 28. How does density change with temperature ?

 

Answer. Density of substance decreases with rises in temperature because for same mass volume  of the body increases due to thermal expansion.

 

 Question. 29. Dene specic gravity or relative density.

 

Answer. Specic gravity (S.G.) or relative density (R.D.) of a substance is dened as the ratio of mass of a given volume  of the substance to the mass of same volume  of water at 4°C.

 

 Question. 30. What is density of water at 4°C ?

Answer. Density of water at 4°C is 1 g cm-3 or 103 kg m-3.

 

 

 Question. 31. What is density of ice at 0°C ?

Answer. Density of ice at 0°C is 0.930  g cm-3 or 930 kg m-3.

 

 

 Question. 32. What is unit of specic gravity or relative density ?

 

Answer. It has  no unit, because it is simply a ratio of two similar quantities.

 

 

 Question. 33. What is the temperature, at which density of water is maximum and  why ?

 

Answer. The density of water is maximum at 4°C. Because the volume  of water is minimum at this temperature. The volume  of water decreases from 0°C to 4°C then  increases with increases in temperature till 100°C.

 

 

Question. 34. What is the density of heaviest liquid ?

 

Answer. Mercury  has  highest density . Its density is 13.6 times the density of water ρ= 13.6 x 103  kg m-3

 

Question. 35. Is density of a body change with places on earth ?

Answer No, because it does vary with 

 

Importance Of The Practicals

Physics is one of the most important subjects in Class 12. As the CBSE exam approaches, students get busy preparing for different subjects. But an essential part of the CBSE exam is the practical exams which consist of 30 marks.

Students must know all the experiments along with theorems, laws, and numerical to understand all the concepts of 12th standard physics in a detailed way. Two experiments (8 + 8 marks) are asked from each section in the practical exam. The experiment records and activities consist of 6 marks, the project has 3 marks and viva on the experiment consist of 5 marks.

The Physics Practicals For Class 12 CBSE is given here so that students can understand the experiments in a better way. Students are suggested to study the theory and law behind the experiment properly before performing the experiment.Also Go through the viva voce questions and answers for each and every experiment which are provided on the website .