Lesson 2: Electromagnetism

Question 1

What is produced around a conducting wire when a current flows through the wire?

Answer 1

• When a current flows through a conducting wire a magnetic field is
  produced around the wire.

Question 2

What are the 2 factors that affect the strength of the magnetic field around a conducting wire?

Answer 2

1.) Depends on current through the wire.
2.) Depends on the distance from the wire (ie. close to the wire, the field lines are close together so the magnetic field is strong - further away, it is weaker.)

Question 3

What is an electromagnet?

Answer 3

• An electromagnet is a solenoid with an iron core.

Question 4

Why are solenoids wrapped around iron cores to form electromagnets?

Answer 4

• Adding an iron core increases the strength of the magnetic field of a solenoid.

Question 5

True or False

The magnetic field around a solenoid has a completely different shape to the magnetic field around a bar magnet.

Answer 5

• FALSE.
• The magnetic field of a solenoid has a similar shape to that of a bar magnet.

Question 6

What can you create (from a wire) to increase the strength of the magnetic field created by the current through the wire?

Answer 6

• A solenoid (a wire with multiple turns.)
• Increases strength of magnetic field created by current through the wire.

Question 7

In a conducting wire, what is the magnetic field around the wire caused by…?

Answer 7

• The magnetic field aound the wire is caused by the current flowing through the wire.

Question 8

What are two words to describe the magnetic field inside a solenoid?

Answer 8

• The magnetic field inside a solenoid is:
• Strong
• Uniform.

Question 9

How can a solenoid’s arrangement (ie. shape) increase the magnetic field produced by the solenoid?

3 different ways!!

Answer 9

1.) Increase size of current = increase strength of magnetic field.
2.) Increased number of turns on coil = increases strength of magnetic field.
3.) Wrap the solenoid around an iron core = increase strength of magnetic field.

Question 10

How do i draw the magnetic field pattern for a straight wire carrying a current?

Answer 10

• Right- Hand Rule.
• Point thumb in direction of current (conventional current positive –> negative.)
• Whichever direction fingers are going in, is the direction of the magnetic field.

Question 11

How can the magnetic effect of a current be demonstrated?

Answer 11

• Set up circuit.
• Wires will have magnetic field.
• Current = off, compass needle lines up with Earth’s magnetic field.
• Switch on current: compass deflects.

Question 12

If you change the direction of the current in a wire, what happens to the magnetic field around the wire?

Answer 12

• The magnetic field around the wire changes direction.

Question 13

Why are electromagnets so useful?

Answer 13

• Can change strength of magnetic field by changing current passing through solenoid.
• Can turn electromagnet on/off.

Question 14

How do I draw the magnetic field pattern for a solenoid?

Answer 14

• The magnetic field points away from positive terminal and points towards negative terminal.
• So where the current is entering the solenoid would be NORTH pole and where current is exitting the solenoid would be the SOUTH POLE.
• Draw lines from noth to south

Question 15

How do relays work using electromagnets?

Relays = devices which switch circuits on/ off.

Answer 15

1.) Two separate circuits.
2.) Low voltage ciruit has electromagnet.
3.) High voltage circuit has two metal contacts and an iron block.
4.) Switch on the low voltage circuit. Electromagnet now has magnetic field around it.
5.) Iron is attracted to the magnetic field and moves so that the contacts (in the high voltage circuit touch and current flows around that circuit.)

Question 16

How do door bells work using electromagnets?

Answer 16

1.) When buzzer is pressed, switch is closed (current flows through the circuit.)
2.) Electromagnet produces a magnetic field around it.
3.) An iron block is attracted to the magnetic field.
4.) Iron block attached to a clapper which in turn moves towards the bell and makes a noise.
5.) Moving iron block leads to break in circuit (so, no magnetic field around electromagnet, so iron block moves back to its original position and the whole process starts again.)