5. Magnetic Fields

Question 1

Magnetic Field: ​

Answer 1

A region surrounding a magnet or current-carrying wire that will exert a force on any other magnet or current-carrying wire placed within it.

Question 2

Magnetic Flux, ​φ​: ​

Answer 2

A value which describes the magnetic field or field lines passing through an area. It is the product of magnetic flux density and the perpendicular area it passes through.

Question 3

Motor Effect: ​

Answer 3

When a current-carrying wire is placed within a magnetic field (non-parallel to the field lines) and experiences a force perpendicular to both the wire and the field lines.

Question 4

What is a Transformer?

Answer 4

A device that changes high alternating voltage at low current to low alternating voltage at high current, and vice versa.

Question 5

Talk through how a transformer works.

Answer 5

In the primary coil, an alternating current producing an alternating voltage is applied
• This creates an alternating magnetic field inside the iron core and therefore a changing magnetic flux linkage
• changing magnetic field passes through to the secondary coil through the iron core
• This results in a changing magnetic flux linkage in the secondary coil and from Faraday’s Law, an e.m.f is induced
• An e.m. produces an alternating output voltage from the secondary coil
• The output alternating voltage is at the same frequency as the input voltage

Question 6

What is the difference between a step u and step down transformer?

Answer 6

• Step-up transformer (increases the voltage of the power source) where Ns > No
• Step-down transformer (decreases the voltage of the power source) where Np > Ns

Question 7

How do Eddy Currents arrise?

Answer 7

Achanging magnetic field (and flux) from the alternating current orvoltage
• Which creates a changing magnetic field in the core that acts against the field that induced them
• An e.m.f is therefore induced
• Acurrent flows, as the core is made from a conducting materialv

Question 8

How can Eddy currents be reduced?

Answer 8

• Laminating the iron core with layers of insulation
• Having a core made from a high resistivity metal

Question 9

How does laminated core stop eddy currents?

Answer 9

• Laminating the core consists of building it with thin layers of metal, instead of a solid metal
• The eddy currents are therefore reduced significantly
• The laminations are insulated from each other, so the current doesn’t flow between them