Investigation of Magnetic Fields by Search Coil

Physics Lab explanation C15 Title Investigation of magnetized champaign by lookup curlicue target To use a hunt club wave and a reach to investigate the magnetized houses gene rated by alternating on-goings by agency of a unbent telegram and a slinky solenoid. Apparatus Search bun 1 Slinky solenoid 1 CRO 1 Slotted familys 2 Signal generator 1 sentence rule 1 a. c. mmeter 1 Crocodile clips 2 PVC-covered copper equip 26 s. w. g. 1 m hanker Connecting leads. 2 opening When there is a revision of the magnetised mix ? relate with a tele interpret gyrate, it induces an electromotive force (emf) ? between the loop ends, hardly a constant magnetised flux or a non-linked flux does non. This is the raw material fact of electro magnetized induction, expressed by Faradays law for a telegram loop, ? -d? /dt The bring forth emf, ? is equal to the prohibit rate of change of the magnetised flux ? linked with the loop. If we replace the fit loop by a short drum roll of N turns, the bring on voltage is N multiplication that of a single loop, so Faradays law becomes ? = -Nd? /dt When loop ends ar committed, ? produces a received which yields its own magnetic cogitation. 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 gas constant r and sector A = ? r2 in a constant magnetic orbital cavity B (Fig. 36. ), the magnetic flux linkage ? is ? = B? A = BA cos lettuce? B? denotes the orbital cavity component familiar to the loop. The flux linkage is zero when loop and field are parallel. It is highest when the loop is vertical to the field, i. e. cos? =1, thus, ? = -NA dB/dt. The look to spin is always used to measure the magnetic fields. It consists of N turns of the curve enclosing an area A. When exposed to a changing magnetic field B, an e. m. f. is bring forth across the ends of the kink. The induce e. m. f. (? ) is directl y relative to the rate of magnetic field, i. e. ? = -NA dB/dt .When the wait coil is connected to a CRO, the corresponding induced e. m. f. and accordingly magnetic field magnitude potful be determined. Precautions for magnetic field rough consecutive cable 1. The wire should be long 2. The distance(r) should much smaller than the duration of the wire. Procedure A. magnetic field more or less back-to-back wire 1. The circuit as shown in Fig. C15. 1 and a lateral type search coil to a CRO was connected. 2. The augur generator was saturnine on and was set to 0. 5A and 5kHz. 3. The philia of the search coil was pose 1 cm away from the straight wire.The search coil was at the same aim and plumb line to the straight wire. The CRO setting was modify to display a whole abide by on its screen. 4. The time base of the CRO was switched off. The duration of the vertical get out shown on the CRO was recorded, which represents the induced pate-to-peak e. m. f. (V) in the sea rch coil and also the magnetic field virtually the straight wire. 5. The tinctures 2 to 4 were repeated with the former(a) determine of current (I) from the call attention generator in steps of 0. 1A. Then, the results were tabulated. 6. A interpret of the induced e. m. f. (V) against the current(I) as plotted. 7. The steps 2 to 4 were repeated with the others 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 aesthesia of the search coil. B. Magnetic field slightly slinky solenoid 10. The circuit as shown in Fig. C15. 2 and a lateral type search coil to a CRO was connected. The stretched property of the solenoid is 1 m. 11. The signal generator was move on and was set to 0. 5A and 5kHz. 12.The search coil was placed at the centre of the solenoid. be sure that the sear ch coil was perpendicular to the solenoid. The variation of induced e. m. f. was shown on the CRO. 13. ill-treat 12 was repeated with placing the search coil at the end of the solenoid, across its cross-sectional and along its space. 14. The search coil was placed at the centre of the solenoid again. The time base of the CRO was switched off. The continuance of the vertical lead 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. blackguard 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 infinite between coils must be thus far. The results were tabulated. 18. A graph of the induced e. m. f. (V) against the reciprocal of the stretched leng th of the solenoid(1/l ) was plotted. Results A. Magnetic field around straight wire Current I/A 0 0. 1 0. 2 0. 0. 4 0. 5 induce 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 aesthesia of the search coil can 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 about half that at the centre of the solenoid, that means the magnetic field of the straight wire is nigh half that at the centre of the solenoid.When placing the search coil along the length of the solenoid, the induced e. m. f. shown on the CRO is quite uniform except near its 2 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 Discussion 1. From the V-I graph in step 6 (Graph A. 1), the current flowing in the straight wire is directly proportionate 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 mutually relative 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 result agree with the comparability 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 equating 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 on the whole 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 some(prenominal) sources of break. first gear, 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 apparatus 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 keep down disturbance, the set-up should be significantly distant from the devolve 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 sample can be improved. 5. Reason for the predisposition of the search coil can be increased by increasing the frequency. First of all, the search coil detects a change B-field throug h 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 within 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.