Solenoids

1. SOLENOIDS
Objectives:
2.3 Map the magnetic field around a
current bearing:
a) straight line conductor
b) solenoid

2. Solenoid
 Wire wrapped in a coil with a current
flowing
 Makes a magnetic field
 Their magnetic fields look like the
magnetic field around a bar magnet.

3. Cores
 A Core is the object that is inserted into
the solenoid, creating an electromagnet.
 Different materials influence the strength
of the electromagnet: Iron, Nickel or
Cobalt.
 Iron is most commonly used because
when you turn off the electricity it
demagnetizes.
 Steel is not used because it remains
magnetized thus creating a permanent
magnet.

4. Solenoid
 2 Methods
 Right Hand rule
 Left Hand rule
 Either Method works

5. Solenoid Rules – Right Hand Rule
 Step #1: Place palm of right hand on
positive end.
Finding
North & South
Poles
- +

6. 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 in
Front of the core
At positive end.
+-

7.  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
- +

8.  Step # 4. If the wire is behind the
tube at the positive end, place your
hand under the tube.
Solenoid Rules – Right Hand Rule
- +
Palm Up
Hand under tube

9.  Double check both palm and
fingers.
 Step #5. Thumb points towards
North. The other end is South.
Solenoid Rules – Right Hand Rule
- +

10. 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).
+-

11. Solenoid Example # 2
1. Find Positive
2. Wire runs in
front of core
3. Place hand on
positive
4. Thumb points
to North
5. Other end is S
6. Magnetic field
runs N (Nerd)
to S (Sexy).
-+

12. Activities
 Work Sheet Mod II, # 3
 Observatory, p. 174, Q. 25

13. Effects of Placing a Compass Near a
Solenoid
1. Label North and South.
2. Draw in arrow on compass.
Example #1
- +
Compass
Remember
That the
Needle is
North
Needle points
to
South

14. More Examples
1. Label North and
South.
2. Draw in arrow on
compass.
Example #2
-+
Compass

15. When Two Solenoids Meet
 Answer: Solenoids would attract.
Would they attract or repel?
+ -
- +
Likes
Repel &
Opposites
Attract

16. Solenoid without a + or -
In a battery
the longer line is
ALWAYS
positive
First
Find the
positive
+ -

17.  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.

18.  Wires with electricity flowing through them
 Like solenoid have N and S poles and
magnetic field.
Straight Line Conductor

19.  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

20.  Step # 2: With your hand open,
your kNuckles are North, and your
finger tipS are South.
Straight Line Conductor
Right Hand Rule
+-

21. Straight Line Conductor
Right Hand Rule
If your hand is
behind the wire,
curl your hand
around the
wire.
-+
-+
kNuckles are
up (N)
finger tipS are
down (S)

22. Placing N & S –
Straight Line Conductor
+
+
+
+
-
-
-
-

23. Effects of a Compass on a
Straight Line Conductor
- +
Compass arrow
Always points
South
Compass

24. Armour Rule:
 For a straight line conductor
connected to a source of electricity,
the finger tips of the right hand
point in the North direction of the
compass.

25. Straight Line Conductor
Examples
-
-
-
- +
+
+
+
A B
C D

26.  Right Hand Rule for Straight Line
Conductors – Thumb points to
negative
 North and South are never on the
ends of the line
 Remember that the compass needle
is North and is attracted to South
 kNuckles are North and finger tipS
are South.

27. Activity
 Worksheet Module 2, # 5
 Page 174, Q. 24

29. 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.

30. 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-

31. Straight Line Conductor
 Current (I):
 flow of electrically charged
particles through a
conductor
 Conventional Current
 Traditionally scientists believed that
current was positive.
I
+

32. Straight Line Conductor
Left 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 Thomson
Electricity produced by
electrons
Electron flow