Page 43 - Physics - XII

The frequency of A.C. mains, f = Mean value of n
2
Result
Frequency of the A.C. mains by sonometer and electromagnet = _____ Hz

The standard value of frequency of A.C. mains = _____ Hz
Diff erence in experimental value and standard value = _____ Hz

Percentage of error Difference 100 _____ %
Standard Value

Precautions
1. Sonometer wire should be of soft iron or other magnetic material.
2. Sonometer wire should be free from kinks and stretched horizontally.
3. The poles of electromagnet should be very close to the wire in the middle of the vibrating segment.

4. The length of the wire while increasing or decreasing should be noted when the amplitude of the
vibrating wire is maximum.
5. The weight of the hanger should be counted while calculating tension in the wire.

Sources of Error

1. The wire may not have uniform area of cross-section.
2. Pulley may not be frictionless.
3. Knife-edges (bridges) may not be sharp.
4. The frequency of A.C. mains may not be stable.
5. Weights may not be correct.

VIVA VOCE

Q1. What type of waves are produced in the wire?
Ans. Transverse stationary waves are produced in the wire.

Q2. What is resonance?
Ans. When the frequency of the externally applied periodic force on a body is equal to its natural vibrations,
the body begins to vibrate with an increased amplitude. This phenomenon is called resonance.

Q3. Why does D.C. repel?
Ans. Main line carrying D.C. has same polarity throughout, (either positive or negative). On touching it,
the body of the person acquires same polarity as that of the main line. The person touching D.C. line
is repelled.

Q4. Why does A.C. attract?
Ans. Main line carrying A.C. has quickly changing polarity. On touching A.C. line, the polarity of the
body of the person also changes. Due to time lag, the body polarity remains opposite to that of the
main line carrying A.C. The person touching the line is attracted.

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