Understanding Magnetism: Concepts, Fields, and Forces

1. Magnetism

2. What is a magnet? • An object that attracts iron containing objects • Has two poles • North and south • Law of poles- • Like poles repel while opposite attract

3. Clicker Question • A bar magnet is divided into two pieces. Which of the following statements is true? • A) the bar magnet is demagnetized • B) the magnetic field of each separated piece becomes stronger • C)the magnetic poles are separated • D) two new bar magnets are created

4. What are magnetic fields? • A region in which the magnetic force can be detected • The magnetic fields go from the north pole to the south pole

5. Clicker Question • Magnetic Field Diagram # 3

6. Magnetic Field Lines • Also called flux lines • Never cross each other • The closer they are the stronger the field

7. Earth’s Magnetic Field • ???

8. Earth’s Magnetic Field • The north pole is actually the south pole of Earth’s magnet! • The magnetic south pole is near the geographic North pole and vice versa. • This is why compasses point to the south pole of a magnet in a magnetic field but we say that compasses point north

9. Earth’s Magnetic Field

10. Clicker Question Which of the following statements is most correct? A.The north pole of a freely rotating magnet points north because the magnetic pole near the geographic North Pole is like the north pole of a magnet. B.The north pole of a freely rotating magnet points north because the magnetic pole near the geographic North Pole is like the south pole of a magnet. C.The north pole of a freely rotating magnet points south because the magnetic pole near the geographic South Pole is like the north pole of a magnet. D. The north pole of a freely rotating magnet points south because the magnetic pole near the geographic South Pole is like the south pole of a magnet.

11. What is magnetism caused by • Caused by moving charges • Any time a charge moves (current) a magnetic field is created • So….electric current can create magnetic fields • Magnetic force is created by two magnetic fields occupying the same space

12. What are magnets? • Electrons have a spin, so there are moving charges in atoms • Most atoms’ electrons are paired up though and spinning in opposite directions, so the fields that are generated are cancelled • When the electrons are not paired up then the fields are not cancelled • These materials can be magnetic

13. Electric Fields Versus Magnetic Fields • Electric Fields • Caused from a positive or negative charges • Charges can be moving or stationary • Fields move from positive to negative • Can be caused by a single charge • Magnetic Fields • Caused from moving charges • Field lines move from north to south pole • Always caused from two poles

14. Magnetic Fields and Current • When there is an electric current a magnetic field (B-field) is created around it • Use the right hand rule • Thumb will point in the direction of the current • Fingers will curl in the direction of the B field

15. Clicker Question • An electric current flows into the page. What is the direction of the magnetic field? • A) to the bottom of the page • B)to the top of the page • C)Clockwise • D)counter-clockwise • E) to the right

16. Clicker Question • A current is flowing to the right, in what direction will the magnetic field be? • A)Into the page • B)out of the page • C)clockwise • D)counter-clockwise • E)to the left

17. Magnetic Fields in Solenoids • Solenoid is a long helically wound coil of wire • Solenoids produce a strong magnetic field by combining several loops • More loops= stronger magnetic field

18. Magnetic Force • A charge moving through a magnetic field experiences a magnetic force • The force is proportional to the • Charge • Velocity • Magnetic field

19. Magnetic Force • Alternative Right Hand Rule • Direction of your palm=magnetic force • Fingers= magnetic field lines • Thumb=velocity of particle • When drawing • An X= into the page • A = out of the page

20. Clicker Question • A positive charge enters a uniform magnetic field as shown. What is the direction of the magnetic force? Velocity is pointed up and fields pointed into page. • A) out of the page • B) into the page • C) downwards • D) to the right • E) to the left

21. Clicker Question • A positive charge enters a uniform magnetic field. What is the direction of the magnetic force? The velocity is to the right and the magnetic field is into the page. • A) out of the page • B) into the page • C) Downwards • D) upwards • E) to the left

22. Multiple Wires • If two wires were parallel to each other and the current was in the same direction, they would attract • If the current is in the opposite direction they would repel

23. Electromagnetic Induction • Changing magnetic fields creates a potential difference (or EMF) in a conductor • So.. Magnetic fields can create currents • This allows physical work to create electrical energy

24. Transformers • Power that is generated for transmission (for homes and buildings) is ramped up (about 100000 V) when it arrives at your home you need it at a lower level (120V) • To convert voltage to a higher or lower value we use a transformer

25. Transformer • Consists of a primary coil and a secondary coil • The current flows through the primary magnetic field • Magnetic field current in secondary coil • We use alternating current for this • When a transformer increases voltage it is called a step up (more secondary coils) • When a transformer decrease voltage it is called a step down (more primary coils)