How DC Motor works?

Another important learning outcome under subtopic 3.2 is to describe:
How a direct current motor works??..this such question can come out in SPM essay paper2

- to describe this, 1st u need to know how the diagram of dc motor looks like.
- then u need to label it, such as which one is the commutator, carbon brush and other component.

DC Motor

Description:

• A direct current (DC) motor which consists of a coil of many turns uses the magnetic turning effect.

• The current flows into the coil through a pair of carbon brushes. The carbon brushes push against commutator.

• then, the commutator changes contact from one brush to another while the coil is turning. This is to keep the coil rotating continuously.

The next thing u need to know is the factors that affect the speed of rotation. The speed of rotation can be increased by:

• increasing Amount of Current
  
• increasing the strength of magnetic field
  
• increasing No. of coils

For better understanding, u should recall back my discussion on magnetic turning effect.

basically, if u understand the whole concept, u can build your own electric motors..watch these videos..give it a try..its FUN :)

Turning effect on a current-carrying coil

In this learning outcome, it is important 4 u to really understand the whole concept. It represents the fundamental principle of how d.c motors work. In SPM physics , it always being asked in Paper1 or Paper2.
So, in this outcome, u must be able to;

-Describe how a current carrying coil in a magnetic field experiences a turning force:
To describe this, 1st u need a wire(conductor) and shape it like a coil in diagram1.

Diagram 1

Then bring this coiled wire in between a permanent magnet. After that u connect both end of the wire to a battery. As a result,current will be supplied through the coil a-b & c-d as shown in diagram 2.

Diagram 2

- From the diagram2 , current in side a-b & side c-d are in different direction.
- In side a-b, apply Fleming Left hand rule, u'll get a force acting downward.
Thus side a-b will pushed downward.

- In side c-d, applying Fleming left hand rule, u'll get a force acting upward.
This caused side c-d to move upward.

- As a result, a turning effect in both sides turn the coil rotating anticlockwise as shown in
diagram 3 below.

Diagram 3

By looking at different view, the turning effect can also be illustrated in diagram 4.

Diagram 4

Factors Affecting the FORCE

Lets now analyse another learning outcome from subtopic 3.2 electromagnet :

Explain the factors that affect the magnitude of the force on a current-carrying condutor in a magnetic field..

This question can come out in paper 2.. basicallyt if u bring a wire which has current flows in it near to a permanent magnet, the wire will be pushed by a FORCE.

The factors that affect the strength of the force depends on:

1. strentgh of magnetic field
- stronger magnet produces stronger magnetic field,thus the force produced is greater

2. amount of current
- the bigger the current, the greater is the force

3. length of conductor(wire)
- the FORCE increases as the length increase

And again i remind u, this direction of force can be determined using FLEMING LEFT HAND RULE

Revise FLEMMING's LEFT HAND RULE.

Combined Magnetic Field Pattern

Under subtopic 3.2, u also need to know :

How to draw pattern of combined magnetic field due to current carrying conductor in the magnetic field?

Ok,it states the word combined magnetic field..so that means there are more than one magnetic field,which is;


i. magnetic field pattern due to current in the conductor(wire), (refer diagram 1)

Diagram 1

ii. magnetic field pattern from poles of permanent magnet,(refer diagram 2)

Diagram 2

When these 2 magnetic field combine, u'll get a pattern like this..(click the diagram below)


As conclusion, when the current carrying conductor is brought near to a permanent magnet, the two fields will interact to produce a resultant FORCE.

(The FORCE direction can be determined using LEFT HAND FLEMING RULE.)

So, in SPM u must understand & know how to draw those combined magnetic field.
I'll post some questions on this soon, till now, BYE!

SPM F5 3.2: Magnetic Force

The next learning outcome, is getting more interesting. By understanding it, u can create so many cool toys & gadgets such as car & chopper remote control . This subtopic requires a complete understanding on certain rules & principles. Lets go in depth,

3.2: Understanding the FORCE on a current carrying conductor in a Magentic Field.
i. U must be able to describe; What happen to a current carrying conductor in magnetic field?? Hmm... when current flows in a wire which then brought near a magnetic field, a magnetic FORCE will be produced. This force, can be illustrated through a rule called FLEMMING LEFT HAND.


This rule is used to determine the direction of force acting upon it.

Ok... how to use it?
Just treat it like a gun :) aiming towards 2 direction, i.e Current & magnetic field.

1st, u need to determine the current direction, then followed by magnetic field direction. Usually students asked me, how to know the direction of magnetic field??
Its simple, the magnetic field always move from north to south
After u've determine both direction of current & magnetic field correctly, automatically your thumb will be pointing towards the direction of force.
By watching these video,it might help u to understand the concept better.