Transformers + Electromagnets

Question 1

Why are step-up transformers used in large-scale electricity transmission TEMPLATE (6)

Answer 1

• increases voltage
• decreases current
• p(in) = p(out)
• transmission current is reduced
• energy losses are reduced
• as current causes heating (but less current so less energy lost)

Question 2

Operation of a step-down transformer (7)

Answer 2

• step-down means secondary voltage is less than primary voltage
• current in the primary coil produces a magnetic field
• current is changing
• causing a changing magnetic field in the core
• core strengthens the magnetic field
• secondary coil experiences a changing magnetic field
• which induces a voltage in the secondary coil

Question 3

How transformers are useful in large-scale transmission of electricity

Answer 3

• STEP UP:
• step-up transformer used before transmission
• voltage is increased before transmission
• current is reduced before transmission
• less heating in transmission cables
• less energy wasted in transmission cables
• STEP DOWN:
• step-down transformer used after transmission
• voltage is decreased after transmission FOR SAFETY

Question 4

Construction of electromagnet

Answer 4

• coil of wire
• core
• current in the wire
• magnetic material (soft iron)

Question 5

Why are step-up transformers used in grid

Answer 5

• increases voltage
• reduces current…
• so less heating of wire
• less energy loss (so greater efficiency)

Question 6

Why are step-down transformers used in grid

Answer 6

• lower voltage
• as towns require voltage for safety (to reduce chance of electrocution + so appliances operate correctly)

Question 7

How is current induced in the core of a transformer

Answer 7

• magnetic field lines cut by core
• induced voltage
• conductors have free electrons (soft iron is a conductor)
• there’s a force on the electrons…
• so the electrons move (which is known as current)

Question 8

How does a step-down transformer work (8)

Answer 8

• decreases voltage
• current in primary coil produces a magnetic field…
• this current is alternating (a.c)…
• causing a changing magnetic field in the core
• core strengthens the magnetic field (at the secondary coil)
• field lines interact with secondary coil…
• this induces a voltage in secondary coil
• transformers won’t work with d.c

Question 9

What does a core do

Answer 9

core strengthens the magnetic field (at the secondary coil)

Question 10

Why step-up transformers are used in grid

Answer 10

• (stepping-up voltage) reduces current
• reducing current reduces heating in the wire

Question 11

Why do transformers not work with d.c

Answer 11

• constant current gives constant magnetic field
• induction (in transformers) requires a changing magnetic field…
• so no voltage will be induced

Question 12

Suitable material for core

Answer 12

• soft-iron
• as it is easy to (de)magnetize

Question 13

What must be done to coil of wire to produce a magnetic field

Answer 13

• pass a current through it

Question 14

Factors that would increase output current of transformer

Answer 14

• increasing input voltage / current
• increasing number of turns on primary coil
• decreasing number of turns on secondary coil

Question 15

Why do we need soft iron core (2)

Answer 15

• iron is soft magnetic material
• core strengthens the magnetic field

Question 16

What does transformer do

Answer 16

• steps up or steps down voltage

Question 17

Transformer won’t work with dc

Answer 17

//

Question 18

What does a.c do

Answer 18

• current in primary coil produces magnetic field
• current is alternating / changing…
• causing a changing magnetic field in the core

Question 19

What happens in secondary coil

Answer 19

• field lines of changing magnetic field of core interaction with secondary coil…
• which induces a voltage in the secondary coil