1. Physics 2.6 Demonstrate understanding of electricity and electromagnetism
Credits 6
This achievement standard involves knowledge and understanding of phenomena, concepts, principles, and relationships related to electricity and electromagnetism, and the use of appropriate methods to solve related problems.

2. Achievement Criteria Achievement Merit Excellence
Identify or describe aspects of phenomena, concepts or principles.
Give descriptions or explanations in terms of phenomena, concepts, principles and/or relationships.
Give concise explanations, that show clear understanding, in terms of phenomena, concepts, principles and/or relationships.
Solve straightforward problems where the concept will be obvious and the solution involves a single process.
Solve problems where the relevent concept is not immediately obvious and may involve rearranging a formula.
Solve complex where two different concepts are needed and the solution involves more than one process.

3. Electromagnetism
Force, F on a current carrying, I conductor of length, L in a magnetic field of strength B,
Force, F on charged particles, q, moving in a magnetic field, B, with velocity, v;
DC motor,
Induced voltage, V, generated across a straight conductor of length, L, moving with velocity, v, in a uniform magnetic field;
Simple generator.

4. Equations

5. Magnetic field around a conductor
When a current flows through a wire it generates a magnetic field around it. On
Off

6. Magnetic field around a conductor
The direction of the field depends upon the direction of the current.

7. Right Hand grip rule
We can determine the direction of the field by using the Right Hand Grip rule.
Current
Field direction

8. A single coil
Closely packed field lines all flowing in the same direction.
Field lines more spread out.

9. The Solenoid
When a current flows through a number of coils or solenoid the field from each coil adds together to produce a magnetic field pattern similar to that produced by a bar magnet. N S N S

10. Right Hand Grip for Solenoids
We can determine the North end of the coil using the Right Hand Grip rule for solenoids.
Current
Field direction

11. Representing magnetic fields
Magnetic field due to a current flowing into or out of the page.
Current into page
Current out of page

12. Force on a current carrying conductor in a magnetic field
When a current, I flows through a conductor of length, L in a magnetic field of strength, B it experiences a force, F.
Force = Magnetic field strength × current × Length
(N) (Tesla, T) (A) (m)
F = BIL
Force, F N S

13. Force on a current carrying conductor in a magnetic field
When a current, I flows through a conductor of length, L in a magnetic field of strength, B it experiences a force, F.
Force = Magnetic field strength × current × Length
(N) (Tesla, T) (A) (m)
F = BIL N S
Force, F

14. Fleming Left Hand Rule Motor Rule
THumb - THrust
First Finger Field
seCond finger
Current
Remember in NZ you drive a MOTOR car on the left.

15. DC Motor
By placing a coil of wire wrapped around a block with a pivot through the middle in a magnetic field, the block will experience a turning force due to the opposing forces.
Force, F N S
Force, F

16. DC motor + - Split ring Coil Brushes N S
Current flows into the coil through the positive wire (left hand brush), and out of the negative wire (right hand brush).
Increasing the number of coils increases the strength of the motor.
Coil
Brushes N S
Split ring + -

17. DC motor
The light half of the split ring is connected to the positive and so current flows in along the left side of the coil.
When vertical, the brushes are in contact with the insulator and no current flows around the coil, so no current flows.
The DARK half of the split ring is now connected to the positive and so current STILL flows in along the left side of the coil. N S + -

18. Force on charged particles moving in a magnetic field
A charge, q moving with velocity, v in a magnetic field of strength, B, will experience a force, F at 90° to the direction of motion (as shown by Fleming’s Left Hand Rule).
Force = Magnetic field Strength × charge × velocity
(N) (Tesla, T) (C) (ms-1)
F = Bqv
Once the charge leaves the field it travels in a straight line.
Magnetic field into the screen.
Centripetal force causes charge to follow a semicircular path whilst in the field.
Charged particle gun

19. Induction
When a wire of length, L moves with a velocity, v through a magnetic field of strength, B it induces a voltage, V across the ends.
Voltage = Magnetic field strength × velocity × length of wire in the field
(V) (tesla, T) (ms-1) (m)
V = BvL
Velocity, v +
The movement of the wire causes the electrons to move down the wire.
This implies that the current flows upwards.
The bottom of the wire becomes negative due to the extra electrons.
Length,L
Magnetic field into page. -

20. Fleming Right Hand Rule Inductor Rule
THumb - THrust
First Finger Field
seCond finger
Current

21. DC Generators
If a motor is caused to turn by some external force then a current is generated as the wires in the coil move through the magnetic field.
A graph of current against time, shows how generation varies as the coil rotates. N S
Current
time - +

22. AC Generators
A more simple generator can be created by using slip rings instead of split rings.
This results in the direction of the current changing halfway through each cycle – alternating current.
A graph of current against time, shows how generation varies as the coil rotates. N S
Current
time + - - +