Page 34 - Physics - XI

9. Now, again try till the range is reduced to 1 g.

10. Now, repeat the above process with fractional weights gradually reducing the range till you reach the
range of 1 mg which gives the correct mass of the body.

11. For the fi nal weighing, keep the doors of the balance closed.

12. Remove the weights with forceps in decreasing order of weights and note in the notebook each weight
removed as shown:

20 g + 20 g + 2 g + 1 g + 500 mg + 100 mg + 50 mg + 5 mg + 2 mg. The mass will be 43.657 g.

13. Repeat steps 4 to 12 for the second object.

Observations
(A) For fi rst object—

(i) Standard masses (full grams) used, m = ____ g, m = ____ g, m = ____ g, m = ____ g
1 2 3 4
(ii) Standard masses from the fractional weight box, m = ____ mg, m = ____ mg, m = ____ mg,
6
7
5
m = ____ mg
8
(B) For second object—
(i) Standard masses (full grams) used, m = ____ g, m = ____ g, m = ____ g, m = ____ g
3
4
1
2
(ii) Standard masses from the fractional weight box, m = ____ mg, m = ____ mg, m = ____ mg,
5
7
6
m = ____ mg
8
Calculations
(i) Mass of the fi rst object = M = (m + m + m + m ) g + (m + m + m + m ) mg
1 1 2 3 4 5 6 7 8
M = [(m + m + m + m ) + (m + m + m + m ) × 10 ] g
–3
2
3
1
7
6
8
4
5
1
M = ______ g
1
(ii) Mass of the second object = M = (m + m + m + m ) g + (m + m + m + m ) mg
5
8
7
6
4
1
2
2
3
M = [(m + m + m + m ) + (m + m + m + m ) × 10 ] g
–3
2 1 2 3 4 5 6 7 8
M = ______ g
2
Result
1. The mass of the fi rst object by physical balance is ____ g.
2. The mass of the second object by physical balance is ____ g.
Precautions
1. The pans should be clean and dry and should rest properly on the knife edges.
2. Physical balance should be levelled with the help of a levelling screw before using it.
3. The beam should be raised very gently without any jerk.
4. The pointer should move equal division on both sides of the central zero mark when the pans are empty.
5. The standard weights should be placed in the right pan and the body to be weighed should be placed
in the left pan.
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