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# Aim: To investigate the factors affecting the e.m.f. induced in a coil due to a varying magnetic field in a neighboring coil.

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Introduction

Physics Formal Lab Report

Name: Yip Ka Man

Class: 6B

Class number: 31

Date: 16th April, 2008

Experiment number: C17

Aim:

To investigate the factors affecting the e.m.f. induced in a coil due to a varying magnetic field in a neighboring coil.

Apparatus:

1 CRO (dual trace)

1 Signal generator

1 Search coil (axial type)

2 Square solenoids (different sizes)

1 d.c. power supply

1 Light-beam galvanometer

1 a.c. ammeter

1d.c. ammeter

1 Rheostat

2 PVC-covered copper wire 26 s.w.g. (2 m long)

1 Magnetic field board

1 Stop watch

Theory:

The electromagnetic induction is a phenomenon that a varying magnetic flux can induce an electromotive force (e.m.f.) in a coil. The induced e.m.f. depending on several factors can be described by the Faraday’s Law of Electromagnetic Induction:

Induced e.m.f. (ε) = -dΦ/dt

Where Φ is the magnetic flux enclosed by a one-turn-coil. Note that the negative sign denotes that the induced e.m.f. and induced current oppose the original change of magnetic flux.

If the magnetic flux linked with a coil of area A, having N turns and at right angles to the magnetic field of flux density B, the total magnetic flux (Φ) is NBA. Hence,

Procedures:

A. Rate of change of magnetic flux

Middle

1. A graph of the induced e.m.f. (ε) against the number of turns (N) was plotted.

B. Number of turns of coil

1. Steps 3 to 4 were repeated with the other values of numbers of turns of the copper coil around the solenoid. The results were tabulated.
 No. of turns(N) 5 7 9 11 13 15 Induced e.m.f.(ε)/mV 0.04 0.05 0.06 0.07 0.08 0.09
1. A graph of the induced e.m.f. against the number of turns was plotted.

C. Cross-sectional area of coil

1. Two square solenoids of different cross-sectional areas were connected in series to the signal generator. The solenoids both had the same number of turns per unit length but one had a larger cross-sectional area than the other.
2. 10 turns of the copper wire were wired tightly around the middle of each solenoid. One copper wire was connected to channel 1 of a dual trace CRO and the other to channel 2. The solenoids were kept well apart from each other.
3. The signal generator was turned on and set to 1 kHz. The CRO setting was adjusted to display both whole traces on its screen.
4. The time base of the CRO was switched off. The length of the vertical trace shown on the CRO was recorded, which represented the induced peak-to-peak e.m.f. in the copper coil for each solenoid.
 Solenoid Large Small Induced e.m.f.(ε)/mV 130 80

Conclusion

From the results in steps 23 and 25 in Part E, it can be concluded that the induced e.m.f. is directly proportional to the rate of change of magnetic flux, i.e. a steady induced e.m.f. will result in a steady rate of change of magnetic flux.The solenoids are placed perpendicular to each other because this ensures that the magnetic field produced in each of the solenoids is not affected by that in the neighboring solenoids.Sources of error:

-There is reaction time of an individual.

-A stopwatch which is fast.

-The surrounding magnetic field of the neighboring solenoids may affect the experimental result.

-The setting and calibration of the CRO is wrong.

Suggested improvements:

-Repeat the experiment several times and take the average data for calculation.

-The time measured by a stopwatch is checked using another watch.

-Place the neighboring solenoids perpendicular to each other.

-Reset the setting and calibration of the CRO.

Conclusion:

From the experiment, it is observed that the factors affecting the e.m.f. induced in a coil due to a varying magnetic field in a neighboring coil are the rate of change of magnetic flux, the number of turns of coil and the cross-sectional area of coil.

This student written piece of work is one of many that can be found in our AS and A Level Electrical & Thermal Physics section.

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