SOLENOIDS
Objectives:2.3 Map the magnetic field around a
current bearing:a) straight line conductor b) solenoid
Solenoid
Wire wrapped around a core (tube)
Have a current flowing through them
Have a magnetic field Their magnetic fields
look like the magnetic field around a bar magnet.
Electromagnet
Cores
A Core is the object that is inserted into the solenoid, creating an electromagnet.
Different materials influence the strength of the electromagnet.
Different metals can be used for the core: iron, steel, nickel or cobalt.
Iron is most commonly used because when you turn off the electricity it demagnetizes.
Metals like steel remain magnetized thus creating a permanent magnet.
Solenoid
2 Methods Right Hand rule
Left Hand rule
Either Method works
Solenoid Rules – Right Hand Rule
Step #1: Place palm of right hand on positive end.
Finding North & South
Poles
- +
Solenoid Rules – Right Hand Rule
Step #2: At the positive end, look to see if the wire is in front or behind the middle tube.
Wire is inFront of the coreAt positive end.
+-
Step # 3: If the wire is in front of the tube at the positive end, place your hand on top of the core.
Solenoid Rules – Right Hand Rule
- +
If the wire is behind the tube at the positive end, place your hand under the tube.
Solenoid Rules – Right Hand Rule
- +
Palm UpHand under tube
Step # 4. Double check both palm and fingers.
Step #5. Thumb points towards North. The other end is South.
Solenoid Rules – Right Hand Rule
- +
Solenoid Examples - # 1
1. Go to the positive
2. Wire runs behind core
3. Hand goes under core & fingers curl up
4. Thumb points N. Other end is S.
5. Lines of Magnetic force run N (Nerd) to S (Sexy).
+-
Solenoid Example # 2
1. Find Positive2. Wire runs in
front of core3. Place hand on
positive4. Thumb points
to North5. Other end is S6. Magnetic field
runs N (Nerd) to S (Sexy).
-+
Activities
Work Sheet Mod II, # 3 Observatory, p. 174, Q. 25
Effects of Placing a Compass Near a Solenoid
1. Label North and South.2. Draw in arrow on compass.
Example #1
- +Compass
RememberThat the Needle is
North
Needle points to
South
More Examples
1. Label North and South.
2. Draw in arrow on compass.
Example #2
-+
Compass
When Two Solenoids Meet
Answer: Solenoids would attract.
Would they attract or repel?
+ -- +
LikesRepel &
OppositesAttract
Solenoid without a + or -
In a batterythe longer line is
ALWAYS positive
FirstFind thepositive
+ -
Right Hand Rule: Use only the right hand to label N and S.
Before solving a problem, always label N and S first.
Red Compass needle is North and is attracted to South.
When the + and the – are not given on a diagram, remember that the longer line on the battery is always positive.
Wires with electricity flowing through them Like solenoid have N and S poles and
magnetic field.
Straight Line Conductor
Step # 1: Using your right hand, point your thumb towards the negative post
Straight Line Conductor Right Hand Rule
- +
Hand on top in this
situation
Straight Line Conductor Right Hand Rule
-+
Or hand behind the conductor As long as the
thumb points tonegative
Step # 2: With your hand open, your finger nails are South and your knuckles are North.
Straight Line ConductorRight Hand Rule
+-
Straight Line ConductorRight Hand Rule
If your hand is behind the wire and you cannot see your finger nails, close your hand.
-+
-+
Knuckles are up (N)Nails are down (S)
Placing N & S – Straight Line Conductor
+
+
+
+
-
-
-
-
Effects of a Compass on a Straight Line Conductor
- +
Compass arrowAlways points
South
Compass
Straight Line ConductorExamples
-
-
-
- +
+
+
+
A B
C D
Right Hand Rule for Straight Line Conductors – Thumb points to negative
North and South are never on the ends of the line
Remember that compass needle is North and is attracted to South (Southern Bell)
Finger tips are South and knuckles are North
Activity
Worksheet Module 2, # 5
Important Symbols & Facts
Magnetic field: represented by B. Current: represented by I. Magnetic Poles:
North pole (N) South Pole: (S)
Magnetic Field: Circular around a straight line.
Solenoid Left Hand Rule
Determine direction by the Left Hand rule – fingers wrap in the direction of the electron flow and thumb points in the direction of the magnetic field (N).
e-
Straight Line Conductor
Current (I): flow of electrically charged
particles through a conductor
Conventional Current Traditionally scientists believed that
current was positive.
I
+
Straight Line ConductorLeft Hand Rule
According to the flow of electrons, your thumb (left hand) follows the direction of the electrons.
Fingers wrap around the wire, giving the shape and direction of the magnetic field.
e-
B
e-
+-
JJ ThomsonElectricity produced by
electrons
Electron flow