Transcript Right Hand Thumb Rule 3

Right Hand Thumb Rule 3
16.2
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
F  IlB sin 
• 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
l  3.2cm  0.032m
I  34mA  0.034 A
B  0.23T
  40.0
F ?
F  IlB sin 
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.
 (0.034)(0.032)(0.23)sin 40.0
 1.6 104 N
F  1.6 104 N , 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:
F
B
IL