Right Hand Thumb Rule

Quick Review 1) How is a solenoid like a bar magnet? 2) Draw a diagram using correct symbols showing a current carrying wire going into the page and the magnetic field it creates. 3) How could you make a solenoid’s magnetic field stronger?

4) Draw the magnetic field and poles for this solenoid.

5. If you grasp a solenoid with your right hand such that your fingers are in the direction of current flow in the wires, and extend your thumb at right angles to the plane of the coil, a. Your thumb will indicate which end of the solenoid is the south end. b. Your thumb will point opposite to the direction of the magnetic field inside the solenoid c. Your thumb will point in the direction of the magnetic field inside the solenoid d. The back of your hand will indicate the north end of the solenoid

What happens when you have 2 interacting magnetic fields?

Force on a Wire A wire's magnetic field will interact with another external magnetic field, possibly experiencing a force depending on its orientation Where the current (I) in the wire is in amperes, the length (l) of the wire is in metres, B is the strength of the magnetic field in tesla (T), and θ is the angle between the wire and the magnetic field. If the wire is parallel to the magnetic field then there is no force on the wire***

Third Right Hand Thumb Rule (palm rule) –hold your hand flat with your four fingers together and your thumb perpendicular to your fingers; –point your thumb in the direction of the positive current (I+) –extend your fingers straight out in the direction of the external magnetic field (B); –your palm will then point in the direction of the force on the wire (F).

Example 1 A 3.2 cm wire is carrying a 34 mA current as shown in the magnetic field below that is directed to the right. The strength of the magnetic field is 0.23 T. Find the force (magnitude and direction) on the wire.

Solution The magnetic field is to the right, and a component of the current is up the page. Using the third right hand rule, Fingers point to the right (with the magnetic field) Thumb points up the page Palm is left facing into the page The force is therefore into the page.

Example 2

Example 3 Find the direction of the current flow.

DOWN!

Think about it… Two wires with current flowing from left to write are parallel. Draw a diagram and prove if they are attracting or repelling each other?

Motors A motor is a device that will convert electrical energy into motion This is possible because when an electric current occurs in a magnetic field, the induced magnetic field in the wire will interact with the magnetic field This will result in a force on the wire which can be determined using Right Hand Rule #3

The Ampere Ampere theorized that the magnetic fields between two charge carrying wires would either result in attractive or repulsive forces Based on this, Ampere was able to develop an equation to describe the magnetic field: