Chapter 21 - Electromagnetism. Flashcards
Describe Han Oersted’s experiment and the result of experiment and what does it prove?
A simple electric circuit is set up with current running from south to north. Two compasses are placed on top and under the wire respectively.
The needle of the compass on top will turn to the east while the needle of the compass under the wire will turn to the west.
A magnetic effect is produced whenever there is a current flow
In Han Oersted’s experiment, a larger current will result in a _______ deflection of the needle of the compass
Larger
How to determine the magnetic field pattern around a CURRENT carrying conductor? e.g wire with current flowing
Use the right hand grip rule, the thumb point that the direction of the current flow, the other four fingers will indicate pattern of the field
A Dot ( . ) indicates that the current direction is ?
coming to ‘you’
A ( + ) indicates that the current is coming ?
going away from ‘you’
The closer the field line, the _______ the magnetic field
Stronger
Magnetic field pattern diagram refer to notes
okay
What are the two method to increase the strength of the magnetic field
Increase the current
Increase the number of the turn of the solenoid
A force on a current carrying conductor in a magnetic field can be produced because?
There are two magnetic field and they interact with each other
How to determine the direction of the force produced by the interaction between magnetic field and current
Use the Fleming’s left hand rule.
The thumb represent the motion/force
The second finger represent the field
The middle finger represent the current
What happen when two parallel wires with current flowing in the SAME direction are placed next to each other? Why?
The two wires will be attracted to each other.
The magnetic field of the two wire cancel out each other in the middle part, while the outer parts of the wires still have magnetic field, thus, the magnetic field strength of the outsides, is stronger then the inside, thus producing a force to push the wires inwards
What happen when two parallel wires with current flowing in the OPPOSITE direction are placed next to each other? Why?
The two wires will repel each other.
The magnetic field of the two wire enhance each other in the middle part, thus, the magnetic field strength of the inside, is stronger then the outside, thus producing a force to push the wires outwards
In a simple motor, how to increase the turning effect of the coil, 2 ways
increase the current
use stronger magnet with strong magnetic field
How does a motor work? (Diagram refer to notes)
When the current pass through the coil, the coil turn in clockwise direction (Fleming’s left hand rule). when the coil finally come to rest in a vertical position. The commutators lose contact with the brushes and make contact with other half. This changes the current direction which in turn changes the force acting on the coil, making the coil continue to move in a clockwise direction. As the current direction is reversed every half a turn, the coil will continue to turn in clockwise direction, achieving the motor effect.
What is the purpose of the commutator in a motor?
It reversed the current direction every half a turn so that the coil continues to turn in one direction ONLY
