Investigation of Magnetic Fields by Search Coil

Physics Lab Report C15 appellation Investigation of magnetised line of productss by face helix target area To use a trainm spin and a background to look into the charismatic scopes generated by alternating currents through a heterosexual person telegram and a slinky solenoid. Apparatus Search loop 1 Slinky solenoid 1 CRO 1 Slotted bases 2 Signal generator 1 amount rule 1 a. c. mmeter 1 Crocodile clips 2 PVC-covered copper wire 26 s. w. g. 1 m abundant Connecting leads. 2 Theory When in that location is a potpourri of the charismatic charismatic subject field ? linked with a wire curl, it induces an electromotive quarter (emf) ? between the loop ends, but a constant magnetised flux or a non-linked flux does not. This is the basic detail of electromagnetic induction, verbalized by Faradays law for a wire loop, ? -d? /dt The bring forth emf, ? is equal to the prejudicious rate of change of the magnetic flux ? linked with the loop. If we deputize the wi re loop by a short scroll of N turns, the bring forth voltage is N sentences that of a single loop, so Faradays law becomes ? = -Nd? /dt When loop ends are connected, ? produces a current which yields its receive magnetic field. Its direction always opposes the flux change d? /dt. This fact is known as Lenzs law and is expressed by the negative sign. For a circular loop of radius r and area A = ? r2 in a constant magnetic field B (Fig. 36. ), the magnetic flux linkage ? is ? = B? A = BA cos? B? denotes the field component normal to the loop. The flux linkage is cypher when loop and field are parallel. It is highest when the loop is perpendicular to the field, i. e. cos? =1, thus, ? = -NA dB/dt. The search handbuild is always used to measure the magnetic fields. It consists of N turns of the coil enclosing an area A. When exposed to a changing magnetic field B, an e. m. f. is bring forth across the ends of the coil. The bring forth e. m. f. (? ) is instantly proportional to the rate of magnetic field, i. e. ? = -NA dB/dt .When the search coil is connected to a CRO, the corresponding induce e. m. f. and hence magnetic field magnitude jackpot be determined. Precautions for magnetic field well-nigh hearty wire 1. The wire should be long 2. The distance(r) should much smaller than the duration of the wire. Procedure A. Magnetic field about unbentforward wire 1. The circuit as shown in Fig. C15. 1 and a lateral type search coil to a CRO was connected. 2. The contract generator was dark on and was set to 0. 5A and 5kHz. 3. The focus on of the search coil was rigid 1 cm away from the straight wire.The search coil was at the equal level and perpendicular to the straight wire. The CRO orbit was adjusted to display a whole trace on its screen. 4. The time base of the CRO was switched off. The space of the perpendicular trace shown on the CRO was recorded, which represents the bring forth peak-to-peak e. m. f. (V) in the search coil and also the ma gnetic field more or less the straight wire. 5. The steps 2 to 4 were reiterate with the early(a) fosters of current (I) from the signal generator in steps of 0. 1A. Then, the results were tabulated. 6. A chartical record of the induced e. m. f. (V) against the current(I) as plotted. 7. The steps 2 to 4 were recurrent with the former(a)s values of distances (r) of the search coil away from the straight wire. The results were tabulated. 8. A graph of the induced e. m. f. (V) against the reciprocal of distance(pic) is plotted. 9. The frequency of the signal generator was varied to change the sensitivity of the search coil. B. Magnetic field around slinky solenoid 10. The circuit as shown in Fig. C15. 2 and a lateral type search coil to a CRO was connected. The stretched length of the solenoid is 1 m. 11. The signal generator was turned on and was set to 0. 5A and 5kHz. 12.The search coil was placed at the centre of the solenoid. Make sure that the search coil was perpendicular t o the solenoid. The variation of induced e. m. f. was shown on the CRO. 13. Step 12 was repeated with placing the search coil at the end of the solenoid, across its cross-section and along its length. 14. The search coil was placed at the centre of the solenoid again. The time base of the CRO was switched off. The length of the vertical trace shown on the CRO was recorded, which represents the induced peak-to-peak e. m. f. (V) in the search coil and also the magnetic field around the solenoid. 15.Step 14 was repeated with the other values of currents (I) from the signal generator in steps of 0. 1A. The results were tabulated. 16. A graph of the induced e. m. f. (V) against the current (I) was plotted. 17. Step 14 was repeated with the other stretched lengths (l) of the solenoid. The distance between coils must be even. The results were tabulated. 18. A graph of the induced e. m. f. (V) against the reciprocal of the stretched length of the solenoid(1/l ) was plotted. Results A. Magn etic field around straight wire Current I/A 0 0. 1 0. 2 0. 0. 4 0. 5 Induced e. m. f. (V)/mV 0 0. 5 1 1. 6 2. 4 4. 1 pic Distance (r) / cm 1 2 3 4 5 1/r /cm 1. 00 0. 50 0. 33 0. 25 0. 20 Induced e. m. f. (V)/ mV 4. 2 3. 2 2. 6 2. 3 2 pic The sensitivity of the search coil advise be increased by increasing the frequency.B. Magnetic field around slinky solenoid When placing the search coil at the centre of the solenoid, across its cross-section, the induced e. m. f. shown on the CRO, i. e. the length of the vertical trace is the maximum, that means the magnetic field of the straight wire is the maximum. When placing the search coil at the end of the solenoid, across its cross-section, the induced e. m. f. shown on the CRO, i. e. the length of the vertical trace is well(p)ly half that at the centre of the solenoid, that means the magnetic field of the straight wire is nearly half that at the centre of the solenoid.When placing the search coil along the length of the solenoid, t he induced e. m. f. shown on the CRO is quite uniform except near its two ends. Current I/A 0. 01 0. 02 0. 03 0. 04 0. 05 0. 06 Induced e. m. f. (V)/mV 1. 4 2. 8 3. 4 4. 2 6 6. 6 picp Stretched length (l ) / m 1 0. 9 0. 8 0. 7 0. 6 0. 5 0. 4 0. 3 1/l /m 1. 00 1. 11 1. 25 1. 43 1. 7 2. 00 2. 50 3. 33 Induced e. m. f. (V)/ mV 1. 6 1. 8 2 2. 2 2. 4 2. 8 3 3. 2 pic intelligence 1. From the V-I graph in step 6 (Graph A. 1), the current menstruation in the straight wire is directly proportional to the induced e. m. f. (V). As the induced e. m. f. ? = -NA dB/dt, the current flowing in the straight wire increases with the magnetic field produced by the current-carrying straight wire. From the V- graph in step 8 (Graph A. 2), the distance from the straight wire is in return proportional to the induced e. m. f. (V). As the induced e. m. . ? = -NA dB/dt, the distance from the straight wire decreases with the magnetic field produced by the current-carrying straight wire. Thus, the resul t agree with the equation pic, where ? 0 is the permeability of free space. 2. From the V-I graph in step 16 (Graph B. 1), the current flowing in the slinky solenoid is directly proportional to the induced e. m. f. (V). As the induced e. m. f. ? = -NA dB/dt, the current flowing in the slinky solenoid increases with the magnetic field produced by the current-carrying solenoid. From the V- graph in step 18 (Graph B. ), its stretched length is inversely proportional to the induced e. m. f. (V). As the induced e. m. f. ? = -NA dB/dt, its stretched length decreases with the magnetic field produced by the current-carrying solenoid. Thus, the result agree with the equation pic, where ? 0 is the permeability of free space and is the number of turns of the solenoid. 3. It is necessary to place the search coil at the same level and perpendicular to the straight wire. Otherwise, the magnetic field cannot cut the search coil completely and ideally. Then, the induced e. m. f. is not the maximum and even there is no induced e. . f. shown on the CRO. As a rollecteesult, the data cd is not accurate. 4. There are several sources of error. First, there is reading error, zero error of ammeter. Secondly, the space between coils is not even. Thirdly, the magnetic field around the straight wire and the slinky solenoid is easily disturbed by other implement nearby. Finally, the search coil is not at right angles to the straight wire and the solenoid, this make the data collected becomes inaccurate. To avoid disturbance, the set-up should be significantly opposed from the return leads and other apparatus.The space between coils is nearly even. The search coil is nearly at right angles to the straight wire and the solenoid Therefore, the experiment can be improved. 5. Reason for the sensitivity of the search coil can be increased by increasing the frequency. First of all, the search coil detects a varying B-field through the current induced in it which is From the deduction, we can see that with A and B0 held constant, which are the area of search coil and the peak value of the varying B-field respectively, the rate of change of magnetic flux ? ncreases with increasing ? which is the angulate frequency with value 2? f, where f is the frequency of the B-field. 6. The Earths field can be ignored because it is a steady magnetic field. Conclusion The magnetic field around a long straight wire carrying a current is directly proportional to the current (I) and inversely proportional to the distance(r) from the wire. The magnetic field inside the solenoid carrying a current is directly proportional to the current (I) and the number of turns (N) but inversely proportional to the length (l ) of the solenoid.