Solenoids

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