Physics 7C SS1 Lecture 8: Electricity & Magnetism Magnetism: RHR 1 & 2 Light as EM wave Polarizers

2 What’s left? 2 Lectures 1 Quiz 4-5 DL Optional review lecture A 1hr15min final exam

3 Field Model of Magnetism A source moving charge creates a magnetic fields in a direction given by RHR1. Another moving charge, placed in a magnetic field, experiences a magnetic force Magnitude given by F=qvBsin  Direction of force given by RHR2  F v B

4 Experiments with magnets and compasses Magnets have poles that repel and attract S N S N S N S N

5 Experiments with magnets and compasses Magnets attract one end of a compass needle and repel the other. S N

6 Iron fillings align with the magnetic field. Dipole Field:

7 Cutting a magnet Slicing a magnet in half results in two weaker magnets, each with a north and south pole.

8 What happens with a compass is brought near a charged rod? a)South pole is attracted to rod b)North pole is attracted to rod c)Neither pole is attracted to rod

9 What happens with a compass is brought near a charged rod? a)South pole is attracted to rod b)North pole is attracted to rod c)Neither pole is attracted to rod

10 Which rule is used to find the magnetic field at point A? a)RHR1 b)RHR2 c)LHR1 d)You can use either hand--just be sure to point your thumb in the direction of the current and curl your fingers to find B! I A

11 Which direction is the magnetic field at point A? 1)Left 2)Right 3)Up 4)Down 5)Into screen 6)Out of screen 7)Away from wire 8)Toward wire 9)Something else I A

12 Which direction is the magnetic field at point A? 1)Left 2)Right 3)Up 4)Down 5)Into screen 6)Out of screen 7)Away from wire 8)Toward wire 9)Something else I A

13 Which direction is the magnetic field at point B? 1)Left 2)Right 3)Up 4)Down 5)Into screen 6)Out of screen 7)Away from wire 8)Toward wire 9)Something else I B

14 Which direction is the magnetic field at point C? 1)Left 2)Right 3)Up 4)Down 5)Into screen 6)Out of screen 7)Away from wire 8)Toward wire 9)Something else I1I1 C I2I2 You may assume I 1 =I 2

15 Which direction is the magnetic field at point C? 1)Left 2)Right 3)Up 4)Down 5)Into screen 6)Out of screen 7)Away from wire 8)Toward wire 9)Something else I1I1 C I2I2 You may assume I 1 =I 2 B tot

16 Magnetic Force Suppose a large magnetic field points downward at every point in the room. What direction is the force on a positive particle traveling along the chalkboards, to your left? 1)Into the board 2)Out of the board 3)Left (along particle path) 4)Right (opposite path) 5)Down 6)Up 7)No Force  v B F = qvBsin  where  is the angle between B and v

17 Magnetic Force Suppose a large magnetic field points downward at every point in the room. What direction is the force on a positive particle traveling out of the board, to the back of the room? 1)Into the board 2)Out of the board 3)Left 4)Right 5)Down 6)Up 7)No Force  v B F = qvBsin  where  is the angle between B and v

18 Magnetic Force Suppose a large magnetic field points downward at every point in the room. What direction is the force on a positive particle traveling upward, toward the ceiling? 1)Into the board 2)Out of the board 3)Left 4)Right 5)Down 6)Up 7)No Force  v B F = qvBsin  where  is the angle between B and v

19 Magnetic Force Suppose a large magnetic field points downward at every point in the room. What direction is the force on a positive particle traveling upward, toward the ceiling? 1)Into the board 2)Out of the board 3)Left 4)Right 5)Down 6)Up 7)No Force  v B F = qvBsin  where  is the angle between B and v

20 Using both RHRs Look at the demonstration. Notice how the wires are bending. If you know the current in the left wire flows upward, which way is the current in the right wire? a)Up b)Down c)Either d)No current

21 Switching Gears: Rethinking Light What “waves” in light? What propagates?

22 Image from

23 A vertical wave traveling through a vertical fence passes unimpeded. The second fence also lets the wave pass. If we place the second fence with horizontal slats, the vertical vibrations cannot pass through the fence. Image from

24 Image from

25

26

27