Grade 11 Physics: Jan 8 – Motor Principle

Watch this:

Yesterday we started talking about solenoids. Today we continued with a few more notes:

How do you increase the strength of a magnetic field in a solenoid?

- increase the current

- increase the number of loops

- decrease the diameter of the loops

- changing the core of the solenoid

(put in a ferromagnetic material)

- speakers

- bells

- hoists

- locks

- MRI

Here's how powerful an MRI's magnetic field can get:

Motor Principle

When a current-carrying conductor is in an external (perpendicular) magnetic field, it experiences a perpendicular force.

This force is given by the right hand rule.

- fingers point in direction of B.

- thumb points in the direction of I.

- palm points in the direction of F.

Here are two views of the right-hand rule.

Here's what it might look like in real life:

The magnitude of this force is:

F = BIL

B = magnitude of magnetic field (Teslas)

I = current (Amperes)

L = length of conductor (meters)

F = force (Newtons)

Using this principle we can build motors!

Here's the simplest motors you can build:

Challenge: Two parallel wires carry current out of the page. Which direction is the force?

I will give you the answer tomorrow!

Practice: Find the direction of the force.

Answers:

Homework:

Keep up with the Unit Outline and try the back of the sheet I handed out yesterday.