1. Physics 4 – Feb 5, 2019 P3 Challenge –
Determine the amount of a) charge and b) energy stored across a 4.0 F capacitor when connected to a 12 V battery.
Get out 11.3 p470 #22-33 for HMK check

2. Objectives/Agenda/Assignment
Ch 5.4 Magnetism
Assignment: p241 #37-46
Agenda:
Homework Review for 11.3
Sources of magnetism
Magnetic field due to a wire
Magnetic flux density
Right hand rule for force
Magnetic force on current carrying wire
Force between two current carrying wires

3. Magnetism Magnetism is another fundamental property of matter.
Demonstrated by electrons, protons and neutrons.
Has a polarity – a north and south pole, gives a direction
Exists as a field – a directional vector field (like an electric field)
Sources include
Particles
Bar magnets (all particles aligned in agreement)
Current carrying wires and solenoids (coiled cylinder of wire)

4. Magnetic fields around sources

5. Direction of magnetic field
Fixed magnet: From south to north (like on a map, up in north)
Due to current in wire: Right hand grip rule – Thumb points in direction of current, fingers curl around wire in direction of circular magnetic field

6. Direction of magnetic field
From a Solenoid: Right hand grip rule – Fingers curl in direction of wire current around the solenoid, thumb points in direction of the magnetic field
Can be determined in lab using a simple compass.

7. Magnetic Flux Density
Magnetic flux density – measures the strength of a magnetic field.
Symbol: B
Unit: Tesla, T
A 1 T magnetic flux density produces a 1 N force on a 1 C charge moving at 1 m/s at right angles to the field.

8. Magnetic Force F = qvBsin
Magnetic fields produce a force on moving charges.
F = qvBsin
Where q is the charge,
v is the speed of the charge,
B is the magnetic flux density, and
 is the angle between the direction of the charge and the direction of the magnetic field.

9. Direction of the magnetic force
The Right Hand Rule: 3 equivalent versions:
Flat hand
Fingers = mag. field
Thumb = charge velocity
Palm = force

10. Direction of the magnetic force
The Right Hand Rule: 3 equivalent versions:
Perpendicular 3 fingers
Thumb = charge velocity
First = mag. field
Middle = force

11. Direction of the magnetic force
The Right Hand Rule: 3 equivalent versions:
Finger curl motion
Fingers point = charge velocity,
Palm/Curl fingers = mag. field
Thumb = force

12. Magnetic force on a current wire
F = BILsin
Where B is the magnetic flux density,
I is the current,
L is the length of wire in the field, and
 is the angle between the current and the magnetic field.

13. Magnetic force on a current wire
Direction of force given by the same right hand rule as for moving charges, a current is a moving charge.
Force directions are defined for a positive moving charge or current
Recall that electrons move in the opposite direction to a current and will experience the magnetic force in the opposite direction.

14. Force between parallel wires
Two sources can combine their magnetic fields in regular vector field addition, just like we saw with electric fields.

15. Force between parallel wires
Two wires can be parallel if the currents flow in the same direction or anit- parallel if the currents flow in opposite directions.
Parallel currents create an attractive force
Antiparallel create a repulsive force

16. Definition of the Ampere
Remember we use the ampere as the fundamental SI base units for all things electrical.
Why? Because it can be standardized through the magnetic force between current carrying wires:
If the force on a 1 m length of two wires that are 1 m apart and carrying equal currents is 2 x 10-7 N, then the current in each wire is defined to be 1 Ampere.

17. Exit slip and homework
Exit Slip – A fixed bar magnet is aligned so that it’s north pole is due north. What is the direction of the force of a charge that is traveling due east past this magnet?
What’s due? (homework for a homework check next class)
p241 #38-44
What’s next? (What to read to prepare for the next class)
Read 11.1 Electromagnetic induction, p