Electromagnetic Induction. Transformer 5/16/11

Transcription

1 ransformer

2 Content 23.1 Principles of electromagnetic induction 23.2 he a.c. generator 23.3 he transformer

3 Learning Outcomes Candidates should be able to: (a) describe an experiment which shows that a changing magnetic field can induce an e.m.f. in a circuit. (b) state the factors affecting the magnitude of the induced e.m.f. (c) state that the direction of a current produced by an induced e.m.f. opposes the change producing it (Lenz s Law) and describe how this law may be demonstrated. (d) describe a simple form of a.c. generator (rotating coil or rotating magnet) and the use of slip rings where needed.

4 (e) *sketch a graph of voltage output against time for a simple a.c. generator. (f) describe the structure and principle of operation of a simple iron-cored transformer. (g) state the advantages of high voltage transmission. (h) discuss the environmental and cost implications of underground power transmission compared to overhead lines

5 v When the switch is closed, iron will magnetize by producing magnetic field lines. v When it produces magnetic field lines, there is a changing magnetic field through solenoid (magnetic field lines are cut b the solenoid. v the changing magnetic field ( field lines cut by the coil) a current is induced showing a momentary deflection.

6 Why the galvanometer shows a momentary deflection? What would happen if we have an a.c supply instead of d.c?

7 A transformer consists of two coils of wire wound on a laminated soft iron core

8 primary coil secondary coil primary voltage (VP) secondary voltage (VS) REMEMBER HA RANSFORMERS ONLY WORK WIH A.C

9 Alternating Voltage supplied to primary coil = Vp A experiment to investigate the effect of the turns ratio on the voltage ratio Alternating Voltage induced in secondary coil = Vs a.c. Supply V V Number of turns in the primary coil = Np Number of turns in the secondary coil = Ns

10 A experiment to investigate the effect of the turns ratio on the voltage ratio A.C. Supply Input coil or Primary coil V Soft Iron Laminated Core and Clip V Output coil or Secondary Coil

11 Conclusion If the number of turns in the SECONDARY coil is LESS than the number of turns in the PRIMARY coil the SECONDARY voltage is LESS than the PRIMARY voltage If the number of turns in the SECONDARY coil is GREAER than the number of turns in the PRIMARY coil the SECONDARY voltage is GREAER than the PRIMARY voltage he ratio of the primary voltage to the secondary voltage is the same as the ratio of the number of turns in the primary coil to the number of turns in the secondary coil Vs / Vp = Ns / Np

12 Converts high alternating voltage to low alternating voltage. Step down transformer Uses: chargers for mobile phones, drills etc., computer circuits, low voltage motors in stereo, CD players, induction furnace etc. High input voltage Low input current Large number of coils Low output voltage High output current Small number of coils REMEMBER HA RANSFORMERS ONLY WORK WIH A.C

13 Converts high alternating voltage to low alternating voltage. Step down transformer Uses: chargers for mobile phones, drills etc., computer circuits, low voltage motors in stereo, CD players, induction furnace etc. High input voltage Low input current Large number of coils Low output voltage High output current Small number of coils REMEMBER HA RANSFORMERS ONLY WORK WIH A.C

14 Step up transformer Converts low alternating voltage to high alternating voltage. Uses: V, computer monitors, power stations to power lines Low input voltage High input current Small number of coils High output voltage Low output current Large number of coils REMEMBER HA RANSFORMERS ONLY WORK WIH A.C

15 Step up transformer Converts low alternating voltage to high alternating voltage. Uses: V, computer monitors, power stations to power lines Low input voltage High input current Small number of coils High output voltage Low output current Large number of coils REMEMBER HA RANSFORMERS ONLY WORK WIH A.C

16 he transmission of electrical energy

17 he transmission of electrical energy village farm town light industry 240V 240V 240V 11 kv National Grid System of Wires 400 kv heavy industry 132 kv 33 kv Power station - transformer

18 he current in the cables produces a heating effect. he heat generated per second (power) by the current is given by: P = I2R watts R is fixed because we cannot change the resistance of the cables so to reduce power loss in the cables we must reduce the current, I. o do this we step up the voltage before transmission which causes the current to be stepped down. After transmission the voltage is stepped down to a safe value and the current is stepped up to be used in homes and factories.

19 ransformer Low Voltage High Current High Voltage Low Current Low Voltage High Current Domestic User Power Station Step-Up ransformer National Grid Step-Down ransformer

20 Click to edit Master text styles Second level hird level Fourth level Fifth level

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