Magnetic Effects of Electric Current

This talk was presented in Summer School Student Workshop 2017 to school students.

Transcript

1. Magnetic Effects of Electric Current Vinay Vaibhav May 29, 2017 The Institute of Mathematical Sciences
2. Table of contents 1. Magnetic Fields and Field Lines 2. Magnetic Field Due to a Current Carrying Conductor 3. Force on a Current Carrying Conductor in a Magnetic Field 4. Electric Motor 5. Electromagnetic Induction 1
3. Magnetic Fields and Field Lines
4. Magnetic Field • Why does a compass needle gets deflected when brought near a bar magnet? • Why do the iron filings arrange in such a pattern? Figure 1: Iron filing near a bar magnet 2
5. Magnetic Field • Magnet can also attract some other materials like iron, cobalt, nickel • This is an example of action at a distance • The magnet exerts its influence in the region surrounding it • How to explain this action at a distance? • Magnet creates − − − − → Magnetic field exerts − − − → Force • Magnetic field has both magnitude and direction Can you think: How does a charge influence other charge placed at some distance? 3
6. Magnetic Field Lines • The specific pattern of iron filings around bar magnet represents the nature of magnetic field. • Magnetic field lines: A pictorial representation of magnetic field • Video1:Magnetic field lines near a bar magnet Figure 2: Field lines near a bar magnet 4
7. Magnetic Field Due to a Current Carrying Conductor
8. Current Carrying Wire • Video2: Field lines near a current carrying wire Why is current carrying wire affecting iron filings? • It has influence similar to bar magnet • The wire is behaving like a magnet • It means, there is a magnetic field around the wire • At first Oersted showed that electricity and magnetism are related • Charge at rest creates − − − − → Electric field • Moving charge creates − − − − → Magnetic field (in addition to Electric field) 5
9. Current Carrying Wire • How to explain the magnetic behaviour of current carrying wire? • Charge at rest creates − − − − → Electric field • Moving charge creates − − − − → Magnetic field (in addition to Electric field) • Demonstration: Electromagnet 6
10. Field Lines Figure 3: Field lines near current carrying wires • Every small section of the wire can be thought as a part of a straight wire • Magnetic field at any point on the axis of the circular loop is along the axis • Direction of field: Right hand thumb rule 7
11. Solenoid Figure 4: Field lines near a solenoid • A solenoid can be considered as a collection of many closed loops • Magnetic field is almost constant inside a long solenoid (field lines parallel) • Solenoid ⇐⇒ Bar magnet 8
12. Force on a Current Carrying Conductor in a Magnetic Field
13. Force on a current carrying wire • There is a force on a magnet if it is placed near current-carrying conductor • The magnet should also exert an equal and opposite force on the current-carrying conductor • Direction of force: Fleming’s left-hand rule 9
14. Reason for force • Charge at rest creates − − − − → Electric field exerts − − − → force on other charges • magnitude |q|E • direction along electric field if q > 0 and opposite to electric field if q < 0. • Moving charge creates − − − − → Magnetic field exerts − − − → force on other moving charges • magnitude |q||v|Bsinθ (where θ is the angle between v and magnetic field) • direction which is perpendicular to both magnetic field and velocity of charge particle. 10
15. Electric Motor
16. Electric motor • Converts electrical energy to mechanical energy • A current carrying loop rotates in magnetic field Figure 6: Schematic of an electric motor • Video3: Electric motor • Demonstration: Electric motor 11
17. Electromagnetic Induction
18. Electromagnetic Induction • Faraday’s Experiments • Experiment with a coil and a bar magnet • Experiment with two coils, one stationary and another (current carrying) moving • Experiment with two stationary coils • Direction of force: Fleming’s left-hand rule • Video4: Electromagnetic induction 12